U. S. DEPARTMENT OF COMMERCE

BUREAU OF STANDARDS

REPORT OF THE

NATIONAL SCREW THREAD

COMMISSION

(REVISED, 1928)

MISCELLANEOUS PUBLICATION, BUREAU OF STANDARDS, No. 89
-


U. S. DEPARTMENT OF COMMERCE

R. P. LAMONT, Secretary BUREAU OF STANDARDS

George K. Burgess, Director

I REPORT

OF THE

NATIONAL SCREW THREAD COMMISSION

(REVISED, 1928)

(AUTHORIZED BY CONGRESS, JULY 18, 1918, H. R, 10852)

AS APPROVED JUNE 22, 1928

MISCELLANEOUS PUBLICATIONS

OF THE

BUREAU OF STANDARDS

No. 89

UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1929
NATIONAL SCREW THREAD COMMISSION

WASHINGTON, D . C.

June 15, 1929.

To Holders of the

192g Report of the

National Screw Thread Commission:

The following revisions have been recommended by

the Bolt, Nut and Rivet Manufacturers Association and

approved by the Sectional Committee on Bolt, Nut and

Rivet Proportions: (See circular letter of April 30,

1529, by Prof. A. E. Norton, Chairman, to members of

Sectional Committee).

Page 135, line 5\ change chamfer on square bolt

11 136 11 2/' heads and nuts from 3O to 25°.

Page 142, Table 69, delete footnote and references

thereto in column 1.

Also change values in tables as follows:

' 1 Change

Pare Table

Size

(column 1)

In

Column

No.

Present

value

New

value

131/64 M

1/2

.521

.%

142 69 9/16 Ji

142 69 5/8

i

'2

• 9375

.906

1.000

.96s

143 70 9/16

i }

31/64

.4-95 .4-73

1/2

.511

.439

143

i44

145

70

71

72 5/gJ

'2

• 9375

.922

1.000

.934

Also, in order to bring your copy up to date

please make the following changes:

Page 220, Fig. 66, title, change "top" to "tap".

Page 251, Table 122, column 12, last line, change

"2 7/g« to "3".

Page 221, Table 106, column 5, insert "12" opposite

2" size to agree with Simplified Practice Recommendation • No. R51-28.

Respectfully,

H. W. Bearcs, Secretary.

ADDITIONAL COPIES

OF THIS PUBLICATION MAY BE PROCURED FROM

THE SUPERINTENDENT OF DOCUMENTS

U. S. GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT

50 CENTS PER COPY
PREFACE

This is the third report of the National Screw Thread Commission, being a

revision of the 1924 report. The general arrangement of the previous report has

s been retained with the exception that specifications for threading tools have been

removed from the body of the report, extensively revised, and included as an

appendix. The designation of the screw-thread standards promulgated by the commission has been changed from "national" to " American National." Other

important revisions are: The addition of sizes above inches to the fine thread

series, but with coarser pitches than those originally published in the progress

report of 1921; increase of the tolerances on minor diameter of nut, over the range of sizes smaller than l^s inches, of the coarse and fine thread series; the

insertion of the 3-inch

V/i threads per inch—size in the coarse-thread series; the substitution of tables of specific pitch diameter tolerances for threads of special diameters, pitches, and lengths of engagement in place of the method of determining such tolerances by adding together increments, thus establishing

consistency with the pitch diameter tolerances specified for the regular thread

series; and revision of head proportions of wood screws. New material added to the body of the report includes the following specifica- tions: Wrench head bolts and nuts and wrench openings; other screw, bolt, and

nut proportions by reference to certain specifications of the American Engineering

Standards Committee 1 and the Federal Specifications Board; an outline of stand- ard practice for Acme screw threads; screw threads for oil well drilling equipment, including pipe, casing, line pipe, cable drilling tool joints, rotary drilling

taper joints, cold drawn and machined working barrels, and sucker rods by refer- ence to specifications published by the American Petroleum Institute; standard

hose connections for welding and cutting torches; rolled threads for screw shells of electric sockets and lamp bases; and a 12-pitch thread series. The specifica- tions for pipe threads are carried over in this report in their original form pending

completion of the work of the new A. S. A. Sectional Committee on the Standardization of Pipe Threads. New material added to the appendixes, besides that mentioned relative to threading tools, includes the following as useful information: Standard designs

of plain and threaded plug and ring gages; specifications covering class 5, wrench fit for threaded studs; common practice as to thread series and class of

fit for screws, bolts, and nuts; and wire methods of measurement of thread

thickness of Acme threads. Acknowledgment for cooperation and assistance essential to the progress of the work is again made to those mentioned in the preface to the 1924 report; namely,

the manufacturers and users of screw-thread products, tools, and gages; the American Society of Mechanical Engineers; the Society of Automotive Engineers;

the American Standards Association 1 and its Sectional Committees on Screw

Threads and Plain Limit Gages; The Federal Specifications Board; the National

Board of Fire Underwriters; the United States Army; the United States Navy;

and the Bureau of Standards; and, in addition, to the A. S. A. Sectional Committee on Bolt, Nut, and Rivet Proportions, the standardization committees of the American Petroleum Institute, the International Acetylene Association, the Gas Products Association, the American Gage Design Committee, and the special N. S. T. C. Committee on Taps.

1 Reorganized as the American Standards Association, Oct. 11, 1928. in

APPROVAL BY THE COMMISSION AND TRANSMITTAL TO

THE SECRETARIES OF WAR, NAVY, AND COMMERCE

Hon. Dwight F. Davis,

Secretary of War

Hon. Curtis D. Wilbur, « Secretary of the Navy

Hon. Herbert Hoover,

Secretary of Commerce

June 22, 1928.

To the honorables the Secretary of War, the Secretary of the

Navy, the Secretary of Commerce : The National Screw Thread Commission, having revised its Progress Report, dated February 11, 1925, herewith submits its report

revised 1928, for your acceptance and approval, in accordance with

Public Act No. 201 (H. R. 10852, 65th Cong.), approved July 18,

1918; as amended by Public Act No. 324 (H. R. 15495, 65th Cong.),

approved March 3, 1919; Public Resolution No. 34 (H. J. 299, 66th

Cong.), approved March 23, 1920; Public Resolution No. 43 (H. J. 227, 67th Cong.), approved March 21, 1922; and Public Act No. 125

(H. R. 264, 69th Cong.), approved April 16, 1926.

George K. Burgess,

Chairman.

E. C. Peck, Lieut. Colonel, U. S. A.,

J. 0. Johnson, Colonel, V. S. A.,

Appointed by the Secretary of War.

H. B. Hird, Commander, V. S. N.,

D. P. Moon, Lieut. Commander, V. S. N.. Appointed by the Secretary of the Navy.

F. O. Wells,

L. D. Burlingame,

Appointed by the Secretary of Commerce from nominations

by the American Society of Mechanical Engineers.

Earle Buckingham,

Geo. S. Case,

Appointed by the Secretary of Commerce from nominations

by the Society of Automotive Engineers.

v
VI APPROVAL ASTD TRANSMITTAL

APPROVAL BY THE SECRETARIES OF WAR, NAVY, AND COMMERCE

The attached report prepared by the National Screw Thread

Commission, in accordance with the law establishing the commission, Public Act No. 201 (H. R. 10852, 65th Cong.), amended by Public Act No. 324 (H. R. 15495, 65th Cong.), Public Resolution No. 34

(H. J. 299, 66th Cong.), Public Resolution No. 43 (H. J. 227, 67th - Cong.), and Public Act No. 125 (H. R. 264, 69th Cong.), is hereby

accepted and approved.

(Signed September 5, 1928) Dwight F. Davis,

Secretary of War.

(Signed September 14, 1928) Curtis D. Wilbur,

Secretary of the Navy.

(Signed July 14, 1928) Herbert Hoover,

Secretary of Commerce.
1928 REPORT OF THE NATIONAL SCREW

THREAD COMMISSION

(Authorized by Congress, July 18, 1918, H. R. 10852)

AS APPROVED JUNE 22, 1928

CONTENTS

Page

Preface in

Section I. Introduction 7

1. Historical 7

2. Need of definite specifications 8

3. Authorization of commission by Congress 8

4. Organization of the commission 10

(a) Preliminary meeting 10

(6) Members 10

(c) Officers 11

(d) Committees 11

(e) Later committees 12

(/) Personnel on European trip 13

(g) Present organization 14

(h) General procedure 14

5. Arrangement of report 15

Section II. Terminology 16

1. Definitions 16

(a) Terms relating to screw threads 16

(6) Terms relating to classification and toler- ances 17

2. Symbols 18

3. Illustrations showing terminology 20

Section III. Screw thread for bolts, machine screws, nuts, tapped

holes, etc . 20

1. American National form of thread 20

(a) Specifications 21

(6) Illustration 22

2. Thread series 22

(a) American National coarse-thread series.. 23

(6) American National fine-thread series 24

3. Classification and tolerances 25

(a) General specifications 25

(6) Classification of fits 28

4. Tables of dimensions 41

5. Gages 60

(a) Fundamentals 60

(6) Specifications for gages 62

1
2 NATIONAL SCREW THREAD COMMISSION

Page Section IV. Screw threads of special diameters, pitches, and lengths

of engagement 78

1. Form of thread 79

2. Thread series 79

3. Classification and tolerances 79

(a) General specifications 80

(ft) Classification of fits 81

4. Tables of dimensions 2 82

(a) Arrangement of tables 82

(6) Rules for use of tables^ 83

(c) Examples 84

5. Specifications for gages 94

(a) Classification of gages and gage toler- ances 94

(b) Thread form of thread plug and ring gages 95

(c) Marking of gages 95

Section V. American National hose-coupling and fire-hose coupling threads 97

1. Form of thread 99

2. Thread series 99

(a) American National hose-coupling threads. 99

(b) American National fire-hose coupling threads 100

3. Allowances and tolerances 100

4. Tables of dimensions 103

5. Gages 104

(a) Gages for American National fire-hose coupling threads 104

Section VI. American National pipe threads 105

1. Form of thread 106

(a) Specifications 106

(6) Illustration 106

2. Symbols 107

3. Thread series 107

(a) American National taper pipe threads 107

(6) American National straight pipe threads, 110

(c) American National lock-nut threads 113

4. Tables of pipe dimensions 114

5. Gages 116

(a) Classification of gages 116

(6) Gaging practices 118

(c) Specifications for gages 119

Section VII. Wood screws 127

1. General specifications

2. Thread series

3. Tolerances on length

(a) Flat and oval head screws

(6) Round-head screwsr 4. American National standard sizes of wood screws.

(a) Steel screws i (6) Brass screws

Section VIII. American National screw, bolt, and nut proportions 2 —

s New material not included in report revised Aug. 19, 1924.
CONTENTS 3

Page

SectionJVIII A. Wrench head bolts and nuts and wrench openings 2 133

1. General requirements 134

(a) Workmanship 134

(6) Screw threads 134

(c) Body diameters 134

(d) Tolerances on length 134

(e) Bolt and screw lengths 134

2. Machine bolts 134

(a) Rough and semifinished bolts 135

(6) Finished bolts 135

3. Tap bolts 135

4. Nuts._.„ __1 135

(a) Rough and semifinished regular nuts 136

(6) Finished regular nuts 136

(c) Castellated nuts 136

(d) Finished and semifinished jam nuts 136

(e) Hexagon light nuts 136

(/) Hexagon and square machine-screw nuts and square stove bolt nuts 136

5. Hexagon-head cap screws 137

6. Wrench openings 137

Section VIII B. Standards for proportions of threaded products indorsed

by the commission 2 148

1. References 148

Section IX. American National Acme screw threads (standard practice) 2 149

1. General and historical 149

2. Terminology ; 150

3. American National Acme form of thread 150

(a) Specifications 150

(6) Illustration 151

4. Thread series 151

5. Classification and tolerances 152

(a) General specifications 152

(6) Classification of fits 153

6. Gages 163

(a) Fundamentals 163

(6) Specifications for gages 163

Section X. Miscellaneous special threads 2 167

Section X A. Screw threads for oil-well drilling equipment 2 167

Section X B. American National standard hose connections for welding

and cutting torches 2 167

1. Standard dimensions 168

2. Optional features _ 169

3. Gages 169

Section X C. American National rolled threads for screw shells of electric sockets and lamp bases 2 174

1. Form of thread 174

2. Thread series 174

3. Gages 175

(a) Gaging of lamp base screw shells 175

(b) Gaging of socket screw shells 175

(c) Tolerances on gages 175

1 New material not included in report revised Aug. 19, 1924.
4 NATIONAL SCREW THREAD COMMISSION

Page Section X D. Screw threads of special diameters, 12 threads per inch

(including railway sizes) 2 176

1. Form of thread " 176

2. Thread series 177

3. Classification and tolerances 177

4. Gages 180 Appendix 1. Derivation of tolerances 181

1. Pitch diameter tolerances 181

(a) Tolerances for fastening screws 181

(b) Tolerances for screw threads of special diameters, pitches, and lengths of engagement. 183

2. Relation of lead and angle errors to pitch diameter

tolerances 183

(a) Diameter equivalent of lead error 183

(b) Diameter equivalent of angle error 184 Appendix 2. Wire methods of measurement of pitch diameter 184

1. Size of wires 184

2. Specification for wires 186

3. Methods of measuring and using wires 186

4. Measurement of pitch diameter of American National

straight threads 187

5. Measurement of pitch diameter of American National

taper threads 188

6. Measurement of pitch diameter of thread ring gages. _ 191

7. Wire methods of measurement of thread thickness of Acme threaded plug gages 2 193 Appendix 3. Control of accuracy of thread elements in the production of threaded product 198

1. Fundamental factors 198

(a) Tool controlled by lead screw 198

(b) Self-leading threading tool 199

2. Cutting of screw threads 199

(a) Single-point tool 199

(6) Thread chaser 200

(c) Tap or die 200

(d) Milling cutter 201

(e) Threading hob 201

3. Rolling of screw threads 201

(a) Threading roll 202

(6) Thread rolling dies 202

4. Finishing of screw threads 203

(a) Grinding 203

(6) Lapping 204 Appendix 4. Specifications for threading tools (recommended practice) 2 ._ 204

1. Tools for American National form of thread (60°) 205

(a) Form of tools for producing screws 205

(1) Inspection of tooth outlines 205

(2) Outline for single-point tool or cutter. _ 207

(3) Outline for multiple-tooth chasers and

hobs 207

1 New material not included in report revised Aug. 19, 1924.
CONTENTS 5

Appendix 4. Specifications for threading tools (recommended practice)

Continued.'

1. Tools for American National form of thread (60°)

Continued. Page

(6) Taps 208

(1) Tap dimensions and tolerances 2 208

(2) Tolerances for taps for special threads-- 219

(3) Shape of cutting edge for taps (and other

internal threading tools) 220

(4) Marking of taps 220

(c) Die-head chasers 2 221

(d) Tap-drill sizes 221

2. Rethreading tools for American National fire-hose threads 2 225

3. Tools for American National pipe threads (60°) 225

(a) Taps 225

(6) Die-head chasers 2 226

(c) Tap-drill sizes 226

4. Tools for American National Acme screw threads

(29°) 2 227

(a) Form of tools for producing screws 227

(1) Outline for single-point tool or cutter 228

(2) Outline for multiple-tooth chasers and hobs 228

(&) Taps 230

(1) Tap dimensions 230

(2) Design of taps 230

(3) Shape of cutting edge of finishing

taps 231 Appendix 5. Class 5, wrench fit for threaded studs (tentative specifications) 2 232

1. Form of thread 232

2. Thread series 232

3. Classification and tolerances 233

(a) General specifications 233

(6) Classification 235

4. Tables of dimensions 235

5. Specifications for threading tools 240

(a) Form of tools for producing studs 240

(&) Taps 240

(c) Tap drills 240

6. Gages and gaging 240

Appendix 6. Common practice as to thread series and class of fit for screws,

bolts, and nuts 241 Appendix 7. (1) Design of gages and (2) gaging practices 241

1. Report of American Gage Design Committee 2 241

(a) History of committee 241

(&) Terminology 244

1 New material not included in report revised Aug. 19, 1924.
b . NATIONAL SCREW THREAD COMMISSION

Appendix 7. (1) Design of gages and (2) gaging practices—Continued.

1. Report of American Gage Design Committee—Con.

(c) American Gage Design standard specifica- tions 245

(1) Plain cylindrical plug gage blanks and handles 245

(2) Thread plug gage blanks and handles.. _ 248

(3) Plain ring gage blanks 248

(4) Thread ring gage blanks 249

2. Gaging practices and types of gages 254

(a) Thread micrometers 255

(6) Thread snap gages 255

(c) Thread ring gages 256

(d) Thread comparators 256

(e) Indicating gages 256

(J) Thread plug gages 256

(g) Plain gages 257

(h) Gear-tooth caliper for thread thickness 257

(i) Testing of gages 257

Index 259
SECTION I. INTRODUCTION

1. HISTORICAL

> The initial accomplishment in the standardization of screw threads

in the United States was the report under date of December 15, 1864,

of the special committee appointed by the Franklin Institute on April

21, 1861, for the investigation of a proper system of screw threads,

bolt heads, and nuts to be recommended by the institute for adoption and general use by American engineers.

In its report this committee recommended a thread system designed

by William Sellers. This thread system specified a single series of

pitches for certain diameters from \i inch to 6 inches, inclusive.

The threads had an included angle of 60° and a flat at the crest and

root equal to one-eighth of the pitch. This system came into general use and was known as the Franklin Institute thread, the Sellers thread, and commonly as the United States thread.

The accomplishments realized in the adoption of the Franklin

Institute, or United States Standard thread, in 1864 were brought

about largely by the great need of standard threads by American

railroads for the development of their lines and equipment. In May,

1868, this thread was adopted by the United States Navy. In

recent years numerous organizations have carried forward the

standardization of screw threads. The American Society of Mechanical Engineers, the Society of Automotive Engineers, the Bureau of Standards, and prominent manufacturers of specialized threaded

products have been the chief influences in standardization of screw

threads in this county.

In England the standardization of screw threads began with the

efforts of Sir Joseph Whitworth in ascertaining shop practice in the

manufacture of screw threads, resulting in the standardization and

adoption of the Whitworth thread system, which found extensive

use in England. This work has been carried forward by the British

Engineering Standards Association, an organization formed in 1901.

While the United States standard thread system fulfilled a great

need in the period of the development of our great railway systems,

it did not fully meet the requirements of modern manufacture be- cause of the need for additional standard sizes and pitches developed

in other industries, and especially because of the need for definitely

specified limiting sizes of threaded parts. To fulfill the first of these

needs a thread system having finer pitches than the United States

standard system was recommended by the Society of Automotive

Engineers, -and a paachine-sciw thread series which provided smaller

7
8 NATIONAL SCREW THREAD COMMISSION

sizes of screws than the United States standard threads was recom- mended by the American Society of Mechanical Engineers. The

progress of machine design and manufacture has established an ex- tensive use of these fine thread series.

2. NEED OF DEFINITE SPECIFICATIONS

The difficulties encountered in obtaining enormous quantities of war material needed by the United States Government during the

World War pointed out to Government establishments as well as manufacturers the need of definite and complete specifications for

material required. Such specifications should be so written that the

qualities desired in the product are stated in definite terms of known

measurable standards, and correctly defined by the largest tolerance

limits compatible with the satisfactory use or performance of the

articles or material for the purpose intended. A prerequisite of

the present-day quantity production of machine parts is standardization of form and dimensions of parts, which involves also the specification of standard limiting dimensions of the manufactured product in

order that interchangeabiiity may be established. The economic

advantages of producing interchangeable machined parts, particularly

when made in different manufacturing plants located at a distance

from each other, which will assemble without difficulty and in a dependable manner, are generally recognized.

The standardization of screw threads, involving as it does the specification of sizes which are necessary to industry, the ehmination of unnecessary sizes, and the securing of interchangeabiiity, is especially

important because of their use in enormous quantities in all varieties

of mechanisms. Such standardization is important to the user of a machine, as well as to the manufacturer, as the user should be able

to buy locally a screw or nut for replacement in case of breakage or wear. A screw-thread fit can not be accurately made with the same

facility as the fit of a plain hole and shaft. In the fit of a plain hole

and shaft only three elements are taken into account in securing a given class of fit, namely, rotundity, diameter, and length; whereas

in a screw-thread fit it is necessary to consider rotundity, length,

major diameter, pitch diameter, minor diameter, angle of thread,

and pitch or lead. A variation in any one of these elements of a screw thread will prevent a good fit, so that it is much more difficult to make a good screw-thread fit than it is to make a plain bearing fit.

3. AUTHORIZATION OF COMMISSION BY CONGRESS

Through the efforts of several of the engineering societies, the

Bureau of Standards, and prominent manufacturers of screw-thread

products, a petition was presented to Congress requesting the appointment of a commission to investigate and promulgate standards of
INTRODUCTION 9

screw threads to be adopted by manufacturing plants under the

control of the Army and Navy and for adoption and use by the public.

As a result of this action the National Screw Thread Commission was

authorized for a period of six months by act of Congress, approved

July 18, 1918 (Public Act No. 201, H. R. 10852, 65th Cong.). Prior

to the expiration of the original term of six months for which the commission was appointed, it became apparent that it would be impossible

to complete in a satisfactory manner the work outlined by the commission. Extensions of time were therefore asked by the commission and granted by Congress in accordance with the following

acts: Public Act No. 324 (H. R. 15495, 65th Cong.); Public Resolution No. 34 (H. J. Res. 299, 66th Cong.); and Joint Public Resolution

No. 43 (H. J. Res. 227, 67th Cong.) The limit on the term of the

commission was then removed by the following act of Congress

(Public Act No. 125, H. R. 264, 69th Cong.):

AN ACT To amend an act to provide for the appointment of a commission to standardize screw threads. Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That an act entitled "An act to provide for the appointment of a commission to standardize screw threads," approved July 18, 1918, as amended by an act approved March 3, 1919, and extended by public resolutions approved March 23, 1920, and March 21, 1922, be, and the same is hereby,

amended so that it will read

:

That a commission is hereby created, to be known as the Commission for the Standardization of Screw Threads, hereinafter referred to as the commission,

Which shall be composed of nine commissioners, one of whom shall be the Director

of the Bureau of Standards, who shall be chairman of the commission; two representatives of the Army, to be appointed by the Secretary of War; two representatives of the Navy, to be appointed by the Secretary of the Navy, and four

to be appointed by the Secretary of Commerce, two of whom shall be chosen from nominations made by the American Society of Mechanical Engineers and

two from nominations made by the Society of Automotive Engineers.

Sec. 2. That it shall be the duty of said commission to ascertain and establish standards for screw threads, which shall be submitted to the Secretary of War,

the Secretary of the Navy, and the Secretary of Commerce for their acceptance

and approval. Such standards, when thus accepted and approved, shall be

adopted and used in the several manufacturing plants under the control of the War and Navy Departments, and, so far as practicable, in all specifications for screw threads in proposals for manufactured articles, parts, or materials to be

used under the direction of these departments.

Sec. 3. That the Secretary of Commerce shall promulgate such standards for use by the public and cause the same to be published as a public document.

Sec. 4. That the commission shall serve without compensation, but nothing

herein shall be held to affect the pay of the commissioners appointed from the Army and Navy or of the Director of the Bureau of Standards.

Sec. 5. That the commission may adopt rules and regulations in regard to

its procedure and the conduct of its business. Approved, April 16, 1926.
10 NATIONAL SCREW THREAD COMMISSION

4. ORGANIZATION OF THE COMMISSION

(a) Preliminary Meeting.—As soon as nominees were selected

by the various organizations to be represented in the commission a preliminary meeting was called at Washington, D. C, on September

12, 1918, by Dr. S. W. Stratton, Director of the Bureau of Standards

and chairman of the commission. At this meeting the organization

of the commission was planned in order that work could be started as soon as formal appointments of the various members of the commission were made. The various commissioners were formally

appointed under date of September 21, 1918.

(6) Members.—In accordance with the act, the following members

have been appointed:

Appointed by the Secretary of Commerce: Chairman : Date appointed Dr. S. W. Stratton, Director of Bureau of Standards, Washington, D. C September 21, 1918. Dr. G. K. Burgess, Director of Bureau of Standards, Washington, D. C, succeeding Dr. S. W.

Stratton April 23, 1923. On nomination by the American Society of Mechanical

Engineers

:

James Hartness September 21, 1918.

F. 0. Wells September 21, 1918. Ralph E. Flanders, succeeding James Hartness___ December 15, 1920. Luther D. Burlingame, succeeding Ralph E. Flanders December 10, 1924. On nomination by the Society of Automotive Engineers : H. T. Herr September 21, 1918. E. H. Ehrman September 21, 191S. Earle Buckingham, succeeding H. T. Herr April 8, 1921. George S. Case, succeeding E. H. Ehrman October 3, 1922. Appointed by the Secretary of War:

E. C. Peck, lieutenant colonel, Ordnance, U. S. Army. September 21, 1918. O. B. Zimmerman, major of Engineers, U. S. Arm}^__ September 21, 1918. John O. Johnson, major of Ordnance, succeeding Maj.

O. B. Zimmerman May 23, 1919. Appointed by the Secretary of the Navy:

E. J. Marquart, commander, U. S. Navy, Bureau of Ordnance September 21, 1918.

S. M. Robinson, commander, U. S. Navy, Bureau of Steam Engineering September 21, 1918. N. H. Wright, commander, U. S. Navy, Bureau of Steam Engineering, succeeding Commander S. M.

Robinson July 14, 1919.

L. N. McNair, commander, U. S. Navy, Bureau of Ordnance, succeeding Commander E. J. Marquart_ October 7, 1919. Joseph S. Evans, commander, U. S. Navy, Bureau of Steam Engineering, succeeding Commander N. H. Wright May 10,fl920.
ORGANIZATION AND PROCEDURE 11

Appointed by the Secretary of the Navy—Continued. Date appointed

S. M. Robinson, commander, U. S. Navy, Bureau of Steam Engineering, succeeding Commander J. S. Evans November 8, 1921.

J. N. Ferguson, commander, U. S. Navy, Bureau of Ordnance, succeeding Commander L. N. McNair__ January 9, 1922. C. A. Jones, lieutenant commander, U. S. Navy, Bureau of Engineering, succeeding Commander S. M.

Robinson March 21, 1922. M. A. Libbey, commander, U. S. Navy, Bureau of Engineering, succeeding Commander C. A. Jones July 19, 1922. John B. Rhodes, commander, U. S. Navy, Bureau of Ordnance, succeeding Commander J. N. Ferguson__ February 20, 1924. T. C. Kinkaid, commander, U. S. Navy, Bureau of Ordnance, succeeding Commander John B. Rhodes. July 3, 1926. Harry B. Hird, commander, IT. S. Navy, Bureau of Engineering, succeeding Commander M. A. Libbey_ February 18, 1927. D. P. Moon, lieutenant commander, U. S. Navy,

Bureau of Ordnance, succeeding Commander T. C. Kinkaid October 29, 1927.

(c) Officers.—The following officers were elected by the commission at the first meeting:

Lieut. Col. E. C. Peck, vice chairman for meetings held in Washington. James Hartness, vice chairman for meetings held outside of Washington.

H. L. Van Keuren, executive secretary. H. W. Bearce, general secretary. Robt. Lacy, first lieutenant of Engineers, U. S. Army, assistant secretary. A. W. Coombs, stenographic reporter. (d) Committees.—The commission resolved itself into the following subcommittees, with authority to call to their aid one or more

experts for counsel. These subcommittees were responsible for compiling and auditing data pertaining to the subject of each committee, and for compiling reports for presentation to the commission

as a whole, for the action of the commission:

F. O. Wells, chairman.

Commander S. M. Robinson.

E. H. Ehrman.

H. W. Bearce, secretary.

Lieut. Col. E. C. Peck, chairman. James Hartness.

E. H. Ehrman.

H. L. Van Keuren, secretary.

F. 0. Wells, chairman.

Commander E. J. Marquart.

Maj. O. B. Zimmerman.

Lieut. Robert Lacy, secretary. James Hartness, chairman.

Lieut. Col. E. C. Peck. Commander E. J. Marquart. H. L. Van Keuren, secretary. 18415°—29 2

Pitches, systems, and form of thread

Classification and tolerances.

Terminology

Gages and methods of test
12 NATIONAL SCREW THREAD COMMISSION

gages.

Boltheads, nuts, and wrenches

Bar sizes.

Instrument

tubing, _ threads and brass

(James Hartness, chairman.

Lieut. Col. E. C. Peck.

F. 0. Wells. {E. H. Ehrman, chairman.

Maj. O. B. Zimmerman.

Commander S. M. Robinson.

(e) Later Committees.—After the publication of the progress

report of 1921, the following additional subcommittees were appointed : Taps, dies, tap drills, and wire [Lieut Col E. c. Peck, chairman.

j Ralph E. Flanders.

(Earle Buckingham.

F. O. Wells, chairman.

Commander L. N. McNair (replaced by- Commander J. N. Ferguson)

.

E. H. Ehrman (replaced by George S. Case). E. H. Ehrman, chairman (replaced by

George S. Case).

Maj. J. 0. Johnson

Commander Joseph S. Evans (replaced by

Commander M. A. Libbey).

Commander L. N. McNair, chairman (re- placed by Commander J. N. Ferguson).

F. O. Wells. Dr. S. W. Stratton (replaced by Dr. George K. Burgess).

Maj. J. 0. Johnson, chairman.

Ralph E. Flanders. Commander Joseph S. Evans (replaced by

Commander M. A. Libbey).

Earle Buckingham.

{Lieut. Col. E. C. Peck, chairman.

Ralph E. Flanders. George S. Case. [Ralph E. Flanders, chairman.

Maj. J. O. Johnson. Commander J. N. Ferguson.

I Earle Buckingham.

After publication of the 1924 report, subcommittees were reorganized as follows:

Prof. Earle Buckingham, chairman.

Commander M. A. Libbey (replaced by

Commander Harry B. Hird).

F. O. Wells. Luther D. Burlingame.

Commander John B. Rhodes, chairman (i placed by Commander T. C. Kinkaid, anc Commander Kinkaid replaced by Lieut. Commander D. P. Moon).

F. O. Wells. George S. Case. Luther D. Burlingame.

Acme and special threads.

Revision of progress report.

Screw threads

industry used in electrical

Bolt heads, nuts, and wrenches.
ORGANIZATION AND PROCEDURE 13

Oil well casing threads.

Stud fits.

Acme threads.

Machine screw

proportions

and stove bolt

Col. John O. Johnson, chairman.

Lieut. Col. E. C. Peck. Commander M. A. Libbey (replaced by- Commander Harry B. Hird)

.

George S. Case.

Lieut. Col. E. C. Peck, chairman.

Prof. Earle Buckingham.

Col. John 0. Johnson. Commander M. A. Libbey (replaced by

Commander Harry B. Hird).

(Lieut. Col. E. C. Peck, chairman.

Luther D. Burlingaine*

Prof. Earle Buckingham.

Commander John B. Rhodes, chairman (re- placed by Commander T. C. Kinkaid, and

Commander Kinkaid replaced by Lieut Commander D. P. Moon).

Prof. Earle Buckingham.

Col. John O. Johnson.

F. 0. Wells, chairman.

Commander John B. Rhodes (replaced by

Commander T. C. Kinkaid, and Commander Kinkaid replaced by Lieut. Commander D. P. Moon).

George S. Case. Luther D. Burlingame.

Luther D. Burlingame, chairman.

Commander John B. Rhodes (replaced by

Commander T. C. Kinkaid, and Commander Kinkaid replaced by Lieut. Commander D. P. Moon).

Prof. Earle Buckingham.

Col. John O. Johnson.

Lieut. Col. E. C. Peck__.

Prof. Earle Buckingham.

George S. Case, alternate Chas. Winter 1 representing organized H. C. Hungerford__j manufacturers.

J. Chester Bath, representing independent

manufacturers

A. C. Danekind J representing users. D. W. Ovaitt___j H. W. Bearce, secretary.

(/) Personnel on European Trip.—In July, 1919, the commission conferred with British and French engineers and manufacturers of screw-thread products, for the purpose of discussing

the tentative report prepared by the commission with reference to

its suitability to serve as a basis for international standardization

of screw threads.

The commission was represented by the following persons:

E. C. Peck (chairman), representative U. S. Army, lieutenant colonel, Ordnance, U. S. Army.

Revision of 1924 report.

Special N. S. T. C. committee on

taps

representing the commission.
14 NATIONAL SCREW THREAD COMMISSION

F. O. Wells (vice chairman), representative A. S. M. E.

L. D. Burlingame, representative A. S. M. E., alternate for James Hartness.

E. Buckingham, representative S. A. E., alternate for H. T. Herr. H. L. Horning, representative S. A. E., alternate for E. H. Ehrman.

J. O. Johnson, representative U. S. Army, major, Ordnance, U. S. Army.

L. B. McBride, representative U. S. Navy, commander, U. S. Navy.

H. C. Dickinson, representative Department of Commerce, U. S. Government, advisory member.

H. W. Bearce, representative Bureau of Standards, U. S. A. (general secretary).

Robert Lacy, representative U. S. Army, first lieutenant Engineers, U. S. Arm}7 (technical secretary).

(g) Present Organization.—At the time of publication of this 1928 revised report the commission comprises the following:

Members:

Dr. George K. Burgess, chairman.

Lieut. Col. E. C. Peck, vice chairman.

F. 0. Wells.

Col. John O. Johnson.

Prof. Earle Buckingham.

George S. Case. Luther D. Burlingame.

Commander Harry B. Hird.

Lieut. Commander Don P. Moon.

H. W. Bearce, secretary.

Staff (Bureau of Standards)

:

D. R. Miller, technical investigator.

I. H. Fullmer, editor. E. G. Hubbell, stenographic reporter.

(li) General Procedure.—In its work of establishing standards

for screw threads, the commission has made particular efforts to secure actual facts concerning the need of standardization and the

economic conditions to be provided for in the production and use

of screw threads.

Steps were taken to secure from various screw-thread authorities

and representative manufacturers and users, testimony as to the

nature of the standards to be adopted for the use of the Government

and for American manufacturers. To secure this information public

hearings were conducted in various industrial centers throughout the

country; and Government officials, authorities on screw threads,

manufacturers, and users of screw-thread products, as well as manufacturers of taps, dies, gages, and other tools required for producing

screw-thread products, were invited to attend these hearings and

present their views on various phases of the subject. In addition,

announcements of the meetings, extending invitations to all interested

to be present, were published in the technical magazines. Topic

sheets were distributed in advance of the hearings in order that wit- nesses could prepare their views on the subjects of the meeting in a definite, concise, and authentic form. ....
ORGANIZATION AND PROCEDURE 15

A large amount of evidence was collected in this way and the opportunity was available for the various members of the commission

to bring out by cross-examination information which could have been

secured in no other way. This evidence was tabulated for the consideration of the commission in formulating its report.

A large number of experiments and tests were made by the Bureau

of Standards to verify the results obtained at the various hearings

and also in connection with the development of tolerances and of

other technical subjects considered by the commission. In addition

to the experiments conducted by the Bureau of Standards, the members of the commission individually conducted experiments and

research work at their own expense.

In view of the fact that international standardization of screw

threads is very desirable, the commission visited Europe in July,

1919, to confer with British and French engineering standards organizations, and while no definite agreements were reached in regard to international standardization of screw threads, it was apparent in

both France and England that the engineers and manufacturers in these countries were anxious to cooperate with the United States in

this work. Such an international standard should be established by

giving consideration to the predominating sizes and standards used

in manufactured products.

The advances made by the commission up to date will facilitate manufacture in case of war, make the best use of labor in our industries in time of peace, increase the safety of travel by rail, steamship, automobile, and airplane, and, in general, will increase the

dependability of all mechanisms. The general adoption of a national

thread system establishes a definite procedure to be followed explicitly

for producing interchangeable threaded products.

The commission, in formulating this report, has acted largely in a judicial capacity, basing its decisions upon evidence received from

authorities on screw-thread subjects and upon the conclusions drawn

by other organizations having to do with standardization of screw

threads. In addition, the various subjects dealt with have been considered with a knowledge of present manufacturing conditions and

with anticipation of further development in the production of screwthread products. Above all, it is the intention of the commission to

facilitate and promote progress in manufacture.

5. ARRANGEMENT OF REPORT

There are included in the body of the report specifications for threaded products and gages, embodying sufficient information to permit the writing of definite and complete specifications for the purchase of screw-thread products. In the appendixes there is arranged
16 NATIONAL SCREW THREAD COMMISSION

supplementary information of both a general and a technical nature,

including such specifications as are not intended to be mandatory.

The specifications in the report have been arranged, as far as possible, by products. For example, one section deals with threads for bolts and nuts, etc., another with hose-coupling threads, another

with pipe threads, etc. As far as practicable, each section is arrangec

in the following order:

1. Form of thread.

2. Thread series. 3. Classification and tolerances.

4. Tables of dimensions.

5. Gages.

SECTION II. TERMINOLOGY

In this report there are utilized, as far as possible, nontechnica

words and terms which best convey alike to the producer and user o: screw threads the information presented.

1. DEFINITIONS

The following definitions are given of the more important terms

used in the report. Definitions of terms which are obviously ele- mentary in character are intentionally omitted.

(a) Terms Relating to Screw Threads.—1. Screw thread.—

A ridge of uniform section in the form of a helix on the surface of a

cylinder or cone.

2. External and internal threads.3—An external thread is a thread on the outside of a member. Example : A threaded plug.

An internal thread is a thread on the inside of a member. Example : A threaded hole.

3. Major diameter {formerly known as "outside diameter").—The

largest diameter of the thread of the screw or nut. The term " major

diameter" replaces the term "outside diameter" as applied to the

thread of a screw and also the term "full diameter" as applied to the thread of a nut.

4. Minor diameter {formerly known as "core diameter").—The

smallest diameter of the thread of the screw or nut. The term

"ininor diameter" replaces the term "core diameter" as applied to the thread of a screw and also the term "inside diameter" as applied

to the thread of a nut.

5. Pitch diameter.—On a straight screw thread, the diameter of an

imaginary cylinder, the surface of which would pass through the

3 These terms are here defined because of possible confusion arising from the fact that an "internal member" has an "external thread," and vice versa. Tor the sake of brevity an external thread is hereinafter referred to as a "screw," and an internal thread as a "nut."
DEFINITIONS OF TEEMS 17

threads at such points as to make equal the width of the threads

and the width of the spaces cut by the surface of the cylinder. On a taper screw thread, the diameter, at a given distance from a reference

plane, perpendicular to the axis of an imaginary cone, the surface of

which would pass through the threads at such points as to make equal

the width of the threads and the width of the spaces cut by the surface

of the cone.

6. Pitch.—The distance from a point on a screw thread to a cor- responding point on the next thread measured parallel to the axis. The pitch in inches == Number of threads per inch

7. Lead.—The distance a screw thread advances axially in one

turn. On a single-thread screw, the lead and pitch are identical; on a double-thread screw the lead is twice the pitch; on a triplethread screw, the lead is three times the pitch, etc.

8. Angle of thread.—The angle included between the sides of the

thread measured in an axial plane.

9. Helix angle.—The angle made by the helix of the thread at the pitch diameter with a plane perpendicular to the axis. 10. Crest.—The top surface joining the two sides of a thread.

11. Root.—The bottom surface joining the sides of two adjacent

threads.

12. Side.—The surface of the thread which connects the crest with the root.

13. Axis of a screw.—The longitudinal central line through the

screw.

14. Base of thread.—The bottom section of the thread; the greatest

section between the two adjacent roots.

15. Depth of thread.—The distance between the crest and the base

of thread measured normal to the axis. 16. Number of threads.—Number of threads in 1 inch of length.

17. Length of engagement.—The length of contact between two

mating parts, measured axially.

18. Depth of engagement.—The depth of thread contact of two

mating parts, measured radially.

19. Pitch line.—An element of the imaginary cylinder or cone

specified in definition 5. 20. Thickness of thread.—The distance between the adjacent sides

of the thread measured along or parallel to the pitch line.

(b) Terms Relating to Classification and Tolerances.—

1. Allowance.—An intentional difference in the dimensions of mating

parts. It is the minimum clearance or the maximum interference

which is intended between mating parts. It represents the condition
18 NATIONAL SCREW THREAD COMMISSION

of the tightest permissible fit, or the largest internal member mated

with the smallest external member. Examples:

One-half inch, class 1, loose fit, American National coarse thread series: Minimum pitch diameter of nut 0. 4500

Maximum pitch diameter of screw . 4478

Allowance (positive) . 0022

One-half inch, class 4, close fit, American National coarse thread series: Minimum pitch diameter of nut . 4500

Maximum pitch diameter of screw . 4504

Allowance (negative) , _ _ _ . 0004

2. Tolerance.—The amount of variation permitted in the size of a

part. Example

:

One-half inch screw, class 1, loose fit, American National coarse thread

series: Maximum pitch diameter ___„ 0. 4478

Minimum pitch diameter . 4404

Tolerance . 0074

3. Basic size.—The theoretical or nominal standard size from which

all variations are made.

4. Crest clearance.—Defined on a screw form as the space between

the crest of a thread and the root of its mating thread.

5. Finish.—The character of the surface on a screw thread or other

product.

6. Fit.—The relation between two mating parts with reference to the conditions of assembly; for example: Wrench fit; close fit; medium fit; free fit; loose fit. The quality of fit is dependent upon

both the relative size and finish of the mating parts.

7. Neutral zone.—A positive allowance. (See "Allowance.")

8. Limits.—The extreme permissible dimensions of a part. Example : One-half inch screw, class 1, loose fit, American National Coarse Thread Series: Maximum pitch diameter 0. 4478 1 These are Minimum pitch diameter . 4404 j the limits.

2. SYMBOLS

For use in formulas for expressing relations of screw threads, and

for use on drawings and for similar purposes, the following symbols

should be used:

Major diameter D

Corresponding radius d

Pitch diameter E

Corresponding radius e Minor diameter K

Corresponding radius k Angle of thread A
SYMBOLS AND MARKING 19

One-half angle of thread a Number of|turns per inch N

Number of threads per inch n

Lead ^=N

Pitch or thread interval.. P =

n

v Helix angle s Tangent of helix angle 14159 X-E Width of basic flat at top, crest, or root F

Depth of basic truncation /

Depth of sharp V thread 1 H

Depth of American National form of thread h Length of engagement Q

Included angle of taper * Y

One-half included angle of taper y Additional symbols for American National Pipe Threads are given

in Section VI.

Symbols are for use on correspondence, drawings, shop and store- room cards, specifications for parts, taps, dies, gages, etc., and on

tools and gages. The method of designating a screw thread by means of symbols

is by the use of the initial letters of the thread series, preceded by

the diameter in inches (or the screw number) and number of threads

per inch, all in Arabic characters, and followed by the classification of

fit in Arabic numerals. If the thread is left hand, the symbol

"L. H." shall follow the number of threads. No symbol is used to distinguish right-hand threads. For screw threads of American

National form but of special diameters, pitches, and lengths of engagement, the symbol "NS" is used. Examples:

American National Coarse Thread Series: To specif}^ a threaded part 1 in. diameter, 8 threads Mark

per inch, class 1 fit l"—8—NC—l

American National Fine Thread Series: Threaded part 1 in. diameter, 14 threads per inch,

class 4 fit l"—14—NF—4

American National Form, Special Pitch: Threaded part 1 in. diameter, 12 threads per inch,

class 2 fit l"—12—NS—2

American National Form, Left-Hand Thread:

Threaded part 1 in. diameter, 12 threads per inch,

class 4 fit l"—12L.H.—NS—4

American National Pipe Threads:

American National taper pipe thread. Threaded

part 1 in. diameter, 113^ threads per inch 1"—11)4,—NPT

American National straight pipe thread 1"—11%—NPS

American National Fire-Hose Coupling Threads and

American National Hose-Coupling Threads: Threaded part 3 in. diameter, 6 threads per inch 3"—6—NH

Threaded part 1 in. diameter, 113^ threads per inch. 1"—11%—NH
20 NATIONAL SCREW THREAD COMMISSION

The number of threads per inch must be indicated in all cases, irrespective of whether it is the standard number of threads for that

particular size of threaded part, or special.

Symbols for Wire Measurements

Measurement over wires M

Diameter of wire G

Corresponding radius g

3. ILLUSTRATIONS SHOWING TERMINOLOGY

Figures 1 and 2 illustrate the use of the terms used in the report as previously defined.

j \*—P/TCH D/AMr~*~

\*11tNOR D/Afif; IK)

SCREW.

In

W

A

HalfAngle

zlixAnc;le(s)

~^PtTCH(fi)

Fig. 1.

Screw thread notation SECTION III. SCREW THREADS FOR BOLTS, MACHINE

SCREWS, NUTS, TAPPED HOLES, ETC.

1. AMERICAN NATIONAL FORM OF THREAD

The form of thread profile specified herein, known previously as the "United States standard or Sellers' profile/ ' is adopted by the

commission and shall hereafter be known as the "American National form of thread."

The American National form of thread shall be used for all screw- thread work except when otherwise specified for special purposes.
AMERICAN NATIONAL FORM OF THREAD 21

(a) SPECIFICATIONS

1. Angle of Thread.—The basic angle of thread (A) between the

sides of the thread measured in an axial plane is 60°. The line bisecting this 60° angle is perpendicular to the axis of the screw thread.

2. Flat at Crest and Root.—The flat at the root and crest of

the basic thread form is Y%Xp, or 0.125 Xp.

3. Depth of Thread.—The depth of the basic thread form is

-k n^nKifw t, 0.649519

A = 0.649519X7?, or h =

where

p = pitch in inches n = number of threads per inch

li = basic depth of thread

Fig. 2.

Screw thread notation

4. Clearance at Minor Diameter.—A clearance shall be pro- vided at the minor diameter of the nut by removing from the crest of the basic thread form an amount such as to provide a depth of thread

not less than 62 to 75 per cent (depending on the size), and not more

than 83 H Pei* cent of the basic thread depth. (See fig. 17.)

5. Clearance at Major Diameter.—A clearance shall be pro- vided at the major diameter of the nut by removing from the basic

thread form an amount such that the width of flat shall be less than

Y%Xp, but not less than )^Xp.
22 NATIONAL SCREW THREAD COMMISSION

(b) ILLUSTRATION There are indicated in Figure 3 the relations as specified herein for the American National form of thread for the minimum nut and maximum screw, free or medium fits. These relations are further shown

in Figures 7 and 9.

Fig. 3.

American National form of thread Note.—No allowance is shown. This condition exists in class 2, free fit, and class 3, medium fit, where

both the minimum nut and the maximum screw are basic. NOTATION n=number of threads per inch H=0.866025 p depth of 60° sharp v thread

h =0.649.519 p depth of American National form of thread %h=0.541266 p maximum depth of engagement

^=0.125000 p width of flat at crest and root of American National form

/=0.108253 p =VsH depth of truncation =y6h 2. THREAD SERIES

It is the aim of the commission, in establishing thread systems for general use, to eliminate all unnecessary sizes and, in addition, to utilize as far as possible present predominating sizes. While from cer- tain standpoints it would have been desirable to make simplifications

in the thread systems and to establish more thoroughly consistent

standards, it is believed that any radical change at the present time

would be out of place and interfere with manufacturing conditions

and would involve great economic loss. The testimony given at the various hearings held by the commission

is very consistent in favoring the maintenance of the present coarse thread and fine-thread series, the coarse-thread series being the

"United States standard" threads, supplemented in the sizes below

one-fourth inch by sizes taken from the standard established by the

American Society of Mechanical Engineers (A. S. M. E.). The fine- thread series is composed of standards that have been found necessary, and consists of sizes taken from the standards of the Society of

Automotive Engineers (S. A. E.) and the fine-thread series of the

American Society of Mechanical Engineers (A. S. M. E.).
AMERICAN NATIONAL COARSE AND FINE THREAD SERIES 23

(a) AMERICAN NATIONAL COARSE-THREAD SERIES In Table 1 are specified the nominal sizes and basic dimensions of

the " American National coarse-thread series." The American National coarse-thread series is recommended for general use in engineering work, in machine construction where conditions are favorable to the use of bolts, screws, and other threaded

components where quick and easy assembly of the parts is desired,

and for all work where conditions do not require the use of fine-pitch

threads.

Table 1.

American National coarse-thread series

Identification Basic diameters Thread data

Sizes Threads

per inch n

Major

diameter D

Pitch diameter E

Minor

diameter K

Metric

equivalent

of major

diameter

Pitch V

Depth

of thread h

Basic width

of flat

.

p/8

Mini- mum

width

of flat at major diameter of nut

p/24

Helix

angle

at basic pitch diameter

Basic

area of section

at root

of thread

4

1 2 3 i 5 6 7 8 9 10 11 13

1 64 Inches

0. 073 Inches

0. 0629 Inches

0. 0527 mm1. 854 Inch0. 01562 Inch0. 01015 Inch

0. 00195 Inch0. 00065 Beg. Min.4 31

Square

inches

0. 0022

2... 56 . 086 . 0744 . 0628 2. 184 . 01786 . 01160 . 00223 . 00074 4 22 . 0031

3 48 .099 . 0855 .0719 2. 515 . 02083 . 01353 . 00260 . 00087 4 26 .0041

4 40 . 112 .0958 .0795 2. 845 . 02500 . 01624 .00312 . 00104 4 45 .0050

5. 40 .125 .1088 .0925 3. 175 . 02500 . 01624 .00312 .00104 4 11 .0067

6 32 .138 . 1177 .0974 3. 505 . 03125 . 02030 .00391 .00130 4 50 .0075

8. 32 .164 . 1437 .1234 4. 166 . 03125 . 02030 .00391 . 00130 3 58 .0120

10 24 .190 .1629 . 1359 4. 826 .04167 . 02706 . 00521 . 00174 4 39 . 0145

12 24 .216 .1889 .1619 5. 486 .04167 . 02706 . 00521 .00174 4 1 .0206 H 20 .2500 .2175 . 1850 6. 350 . 05000 . 03248 .00625 .00208 4 11 .0269 Me 18 .3125 .2764 . 2403 7. 938 . or>,->.-><; . 03608 .00694 .00231 3 40 .0454 H 16 . 3750 .3344 .2938 9. 525 . 06250 .04059 .00781 .00260 3 24 .0678 M« 14 .4375 .3911 .3447 11.113 .07143 .04639 .00893 .00298 3 20 .0933

13 .5000 .4500 .4001 12. 700 . 07692 . 04996 .00962 .00321 3 7 .1257

9/)6 12 .5625 . 5084 . 4542 14. 288 . 08333 . 0.5413 . 01042 . 00347 2 59 .1620 k 11 . 6250 .5660 .5069 15. 875 . 09091 . 05905 .01136 .00379 2 56 .2018 H- 10 . 7500 .6850 . 6201 19. 050 .10000 . 06495 . 01250 .00417 2 40 .3020

7/i 9 . 8750 .8028 .7307 22. 225 .11111 . 07217 . 01389 .00463 2 31 .4193

1 8 1.0000 .9188 .8376 25. 400 . 12500 .08119 . 01562 . 00521 2 29 .5510 m 7 1. 1250 1. 0322 .9394 28. 575 . 14286 . 09279 .01786 . 00595 2 31 .6931 IK 7 1. 2500 1.1572 1.0644 31. 750 . 14286 . 09279 . 01786 . 00595

.00694 2 15 .8898 m— 6 1. 5000 1.3917 .1. 2835 38. 100 . 16667 . 10825 . 02083 2 11 1. 2938

5 1. 7500 1. 6201 1. 4902 44. 450 .20000 . 12990 . 02500 . 00833 .00926

2 15 1. 7441 2 - m

4H

4

2.0000 1. 8557 1. 7113 50. 800 . 22222 . 14434. . 02778 2 11 2. 3001 2H 2. 2500 2. 1057 1. 9613 57. 150 . 22222 .14434 . 02778 . 00926 1 55 3. 0212

2V> 2. 5000 2. 3376 2. 1752 63. 500 .25000 . 16238 .03125 .01042 1 57 3. 7161 m 4 2. 7500 2. 5876 2. 4252 69. 850 . 25000 . 16238 . 03125 . 01042 1 46 4. 6194

3 i. 4 3.0000 2. 8376 2. 6752 76. 200 .25000 . 16238 . 03125 .01042 1 36 5. 6209

3 3tt 3.0000 2. 8144 2. 6288 76. 200 . 28571 . 18558 . 03571 . 01190 1 51 5. 4276

Optional. Standard for marine work.
24 NATIONAL SCREW THREAD COMMISSION

(b) AMERICAN NATIONAL FINE-THREAD SERIES In Table 2 are specified the nominal sizes and basic dimensions of the "American National fine-thread series." The American National fine-thread series is recommended for general use in automotive and aircraft work, for use where the design

requires both strength and reduction in weight, and where special

conditions require a fine thread.

Table 2.American National fine-thread series

Identification Basic diameters Thread data

0-

1-

2-

3..

4_. 5-

6„

8__. 10. 12. HHb

3/8-

HU1-. w

w2... 2U

2H

2%

Threads

per

inch n

Major

diameter D

Inches

0. 060

.073 .086

.099 .112

.125

.138 .164

.190

.216

.2500

.3125

.3750

.4375 .5000

.5625

6250 .7500

.8750

1.0000

1. 1250

1. 2500

1. 5000

1. 7500

2. 0000

2. 2500

2. 5000

2. 7500 3.0000

Pitch diameter E

Inches

0. 0519

.0640

.0759 .0874

.0985

.1102

.1218

.1460

.1697 .1928

.2268

.2854

.3479

.4050

.4675

.5264

.9536

1. 0709

1. 1959

1. 4459

1. 6850

1. 9350

2. 1688

2. 4188

2. 6688

2. 9188

Minor

diameter K

Metric

equivalent of major

diameter

Inches

0.0438

.0550

.0657

.0758 .0849 .0955

.1055

.1279

.1494

.2036

.2584 .3209

.3725 .4350

.4903

.5528 .6688

.7822 .9072

1. 0167

1. 1417

1. 3917

1. 6201

1. 8701

2. 0876

2. 3376

2. 5876

2. 8376

mm

1.524

1.854

2. 184

2. 515

2. 845

3. 175

3. 505

4. 166

4. 826 5.486

6. 350

7. 938

9. 525 11.113

12. 700

14.288

15. 875

19. 050

22. 225

25. 400

28. 575

31. 750

38. 100

44. 450

50.800

57. 150

63. 500

69. 850

76. 200

Pitch V

Inch

0. 01250

. 01389

. 01562

.01786

. 02273

. 02500

. 02778

. 03125

. 03571

. 03571

. 04167

.04167 .05000

.05000

. 05556

. 05556 .06250

. 07143

. 07143

. 08333

. 08333

. 08333 .10000

.10000

. 12500

. 12500

. 12500

. 12500

Depth

of thread

h

Inch

0. 00812

.00902

. 01015

. 01160

. 01353

. 01476

. 01624

. 01804

. 02030

. 02320

. 02320

. 02706

. 02706

. 03248

. 03248

. 03608

. 0360S

. 04059

. 04639

.04639

. 05413

. 05413

. 05413

, 06495

,06495

. 08119

, 08119

, 08119

, 08119

Basic width

of flat P/8

Inch

0. 00156

.00174

.00195 .00223

.00260

.00284

. 00312

.00347

. 00391 .00446

.00446

. 02521

. 00521

. 00625

. 00625

. 00694

.00694

. 00781

. 00893

.00893 .01042 .01042

. 01042

. 01250

. 01250

. 01562

. 01562

. 01562

. 01562

Mini- mum

width

of flat at major di- ameter

of nut

P/24

Inch

0. 00052

.00058

.00065 .0C074

.00087 .00095

.00104

. 00116 .00130

.00149

. 00149 .00174

. 00174 .00208

. 00208

.00231

. 00231 .00260

.00298 .00298

.00347

. 00347

. 00347 .00417

.00417

.00521 .00521

. 00521

. 00521

Helix

angle

at basic pitch diameter

Beg. min.

Basic

area of section

at root

of thread

4

Square

inches 0.0015

.0024

.0034 .0045

.0057 .0072

.0087 .0128

.0175

.0226 .0326

.0524

.0809 .1090

.1486

.2400

.3513

.4805 .6464 .8118

1. 0238

1. 5212

2. 0615 2.7468

3.4228

4.2917

5. 2588

6. 3240
FITS, ALLOWANCES, AND TOLERANCES 25

3. CLASSIFICATION AND TOLERANCES

There are established herein for general use four distinct classes of screw-thread fits as specified in the following brief outline. These

four classes of fits, together with the accompanying specifications, are

for the purpose of insuring the interchangeable manufacture of

v screw-thread parts throughout the country.

It is not the intention of the commission arbitrarily to place a

general class or grade of work in a specific class of fit. Each manufacturer and user of screw threads is free to select the class of fit best adapted to his particular needs. The tolerances and dimensions

for four classes of fit are given in Tables 3 to 14, inclusive, and summarized in Tables 15 and 16. Includes screw-thread work of rough commercial quality, where the threads must

assemble readily, and a certain amount

of shake or play is not objectionable.

'Includes the great bulk of screw-thread work of ordinary quality, of finished and semifinished bolts and nuts, machine

screws, etc. Includes the better grade of interchangeable screw-thread work.

Includes screw-thread work requiring a fine snug fit, somewhat closer than the medium

J fit. In this class of fit selective assembly

of parts may be necessary. An examination of the dimensional specifications for the various

classes of fit shows that a screw made to one class of fit may be used

with a nut or tapped hole made to some other class of fit. The

resulting quality of fit may represent an intermediate class or may

approximate one of the classes of fit adopted as standard. The use

of different classes of fit on the screw and threaded hole may be

justified when equipment available is such that one member can be

economically produced to a higher accuracy than the other. For

instance, common commercial machine screws are made to class 2, free fit, while machine screw nuts are commonly supplied in class 1, loose fit ; or, ground taps may make it practicable to produce class 3 nuts for use with class 1 or class 2 screws.

(a) GENERAL SPECIFICATIONS The following general specifications apply to all classes of fit specified for the American National coarse-thread series and the

American National fine-thread series.

1. Uniform Minimum Nut.—The pitch diameter of the minimum

threaded hole or nut corresponds to the basic size.

Class 1, loose fit

Class 2, free fit

Class 3, medium fit.

Class 4, close fit
26 NATIONAL SCREW THREAD COMMISSION

2. Unifokm Minor Diameter of Nut.—The minor diameter of the threaded hole or nut, of any given size and pitch, is the same for

fits of classes 1 to 4, inclusive.

3. Length of Engagement.—A length of engagement equal to the basic major diameter is the basis of the tolerances specified herein

for screw-thread products.

4. Tolerances.4—(a) The tolerances specified represent the ex- treme variations permitted on the product.

(b) The tolerance on the nut is plus, and is applied from the basic

size to above basic size.

(c) The tolerance on the screw is minus, and is applied from the

maximum screw size to below the maximum screw size. (d) The pitch diameter tolerances for a screw and nut of a given

class of fit are the same.

(e) Pitch diameter tolerances include lead and angle variations.

(See footnote 1, Tables 3, 4, 5, and 6.) (/) The tolerances on the major diameters of class 1, loose fit, or

class 2, free fit screws are twice the tolerance values allowed on the

pitch diameters of the same respective classes, and for the corre- sponding thread series, with the following exceptions: (1) Threads

above 1H> inches diameter of the American National fine-thread

series, class 1, loose fit and class 2, free fit, have major diameter

tolerances equal to twice the pitch diameter tolerances of the corre- sponding pitches and fits of the American National coarse-thread

series. (2) On class 2, free fit, American National coarse-thread

series, externally threaded parts of unfinished, hot-rolled material,

the same tolerances on major diameter are applied as on class 1, loose fit screws. The tolerances on the major diameters of class 3, medium fit and class 4, close fit screws, American National coarse- thread series, are the same as those on class 2, free fit finished screws of the same thread series; and for the American National fine-thread

series are the same as those on class 2, free fit of that series.

(g) The minimum minor diameter of a screw of a given pitch is such as to result in a basic flat (\4Xp) at the root when the pitch

diameter of the screw is at its minimum value. When the maximum

screw is basic, the minimum minor diameter of the screw will be below

the basic minor diameter by the amount of the specified pitch diameter

tolerance.

Qi) The maximum minor diameter of a screw of a given pitch may

be such as results from the use of a worn or rounded threading tool,

when the pitch diameter is at its maximum value. In no case, however, should the form of a thread, as results from tool wear, be such

as to cause the screw to be rejected on the maximum minor diameter

by a "go" ring gage, the minor diameter of which is equal to the

minimum minor diameter of the nut.

* Recommendations and explanations regarding the application of tolerances are given in Appendix 1.
FITS, ALLOWANCES, AND TOLERANCES 27

is its 5

.

Illustration of tolerances, allowance (neutral space), and crest clearances

for class 1, loose fit 18415°—29 3
28 NATIONAL SCREW THREAD COMMISSION

(i) The maximum major diameter of the nut of a given pitch is such as to result in a flat equal to one-third of the basic flat (%4 Xp)

when the pitch diameter of the nut is at its maximum value. When

the minimum nut is basic, its maximum major diameter will be above

the basic major diameter by the amount of the specified pitch diameter tolerance plus two-ninths of the basic thread depth.

(j) The nominal minimum major diameter of a nut is the basic

major diameter. In no case, however, should the minimum major

diameter of the nut, as results from a worn tap or cutting tool, be

NOTE: DOTTED LINE SHOWS BASIC SlZ£.

NOTAT/ON

0= major diameter

E'pitch diameter

K» minor diameter h-.OZZS* basic thread depth

SCREW NUT

Fig. 5.

Illustration of loosest condition for class 1, loose fit, one-fourth inch, 20 threads such as to cause the nut to be rejected on the minimum major diameter by a " go" plug gage made to the standard form at the crest.

Qc) Tolerances are based on the pitch of the thread and a length of engagement equal to the basic major diameter, but may be used for lengths of engagement up to 1% diameters. (For longer lengths of engagement see Section IV, p. 78.)

(b) CLASSIFICATION OF FITS

1. Class 1 Loose Fit.—(a) Definition.—The loose-fit class intended to cover the manufacture of threaded parts where quick

and easy assembly is necessary and a considerable amount of shak

or play is not objectionable
FITS, ALLOWANCES, AND TOLERANCES 29

This class has an allowance on the screw to permit ready assembly even when the threads are slightly bruised or dirty.

(b) Minimum nut basic.—The pitch diameter of the minimum nut

of a given diameter and pitch corresponds to the basic pitch diameter,

as specified in the tables of thread series given herein, which is computed from the basic major diameter of the thread. The pitch

SC/?£>V nut

Fig. 6.

Illustration of tightest condition for class 1, loose jit, one-fourth inch, 20 threads

NOTATION D=major diameter E—pitch diameter K=minor diameter A=0.0325=basic thread depth diameter of the minimum nut is the theoretical pitch diameter for

that size.

(c) Maximum screw below basic.5—The dimensions of the maximum

screw of a given pitch and diameter are below the basic dimensions

as specified in the tables of thread series given herein, which are computed from the basic major diameter of the threads, by the

amount of the allowance given in Table 3.

» The maximum minor diameter of the screw is above the basic minor diameter, as shown in Figure 4.
30 NATIONAL SCREW THREAD COMMISSION

(d) Allowance and tolerance values.—Allowances and tolerances are

specified in Table 3. Table 3.

Class 1, loose fit, allowances and tolerances for screws and nuts

Threads per inch Allowances

Pitch diameter

tolerances 1

Lead

errors consuming

one-half

of pitch- diameter

tolerances 2

Errors in half-angle consuming

one-half

of pitch- diameter

tolerances

72

64. 56

48. 44

40 : 36

32.. 28

2420

18. 1614

1312

11. 10 (American National coarse)

10 (American National fine)—

9

8 (American National coarse)

.

8 (American National fine) 7...

6.54H

43H

Inch

0.0007

.0007

.0007

.0008

.0009

.0009 .0010

.0011

.0011 .0012

.0013

.0015 .0016

.0018

.0021 .0022

.0024

.0026 .0028

.0028

.0031 .0034

.0034 .0039

.0044 .0052

.0057

.0064 .0073

Inch

0. 0024

.0025

.0026

.0028

.0031 .0032

.0034

0043 0046

0051 0057

0063 0070

0074

,0079

,0085

,0092 ,0132

.0100

,0111 ,0145

,0124

,0145

,0169

,0184

,0204

,0229

Inch

0.0007

.0007

.0009

.0010

.0010

,0011 .0012

.0013 .0015

.0016

.0018

0021

,0023

,0025

,0027

,0029

,0032 ,0042

,0036

,0042

,0049

,0053 ,0059

,0066

Beg. Min.

3 40

40

32

1 The tolerances specified for pitch diameter include all errors of pitch diameter, lead, and angle. The full tolerance can not, therefore, be used on pitch diameter unless the lead and angle of the thread are perfect. Col- umns 4 and 6 give, for information, the errors in lead (per length of thread engaged) and in angle, each of which can be compensated for by half the tolerance on the pitch diameter given in column S. If lead and angle errors both exist to the amount tabulated, the pitch diameter of a bolt, for example, must be reduced by the full tolerance or it will not enter a basic nut or gage.

1 Between any two threads not farther apart than the length of engagement. 2. Class 2, Free Fit.—(a) Definition.—The free-fit class is intended

to apply to interchangeable manufacture where the threaded members

are to assemble nearly, or entirely, with the fingers, where a moderate

amount of shake or play between the assembled threaded members is not objectionable, and where no allowance is required. This class includes the great bulk of fastening screws.

(b) Minimum nut basic.—The pitch diameter of the minimum nut

of a given diameter and pitch corresponds to the basic pitch diameter,

as specified in tables of thread series given herein, which is computed

from the basic major diameter of the thread.
FITS, ALLOWANCES, AND TOLERANCES

III*

• B4S*C THREAD

Heavy Z//v^ Shows

3as/c <S/ze

Fig. 7.

Illustration of tolerances and crest clearances for class 2, free fit
32 NATIONAL SCREW THREAD COMMISSION

NOTE: DOTTED LINE SHOWS BASIC SIZE

NOT/IT/ON

D~ major diameter

E=pitch diameter

K a minor diame te

r

h 0325 - basic thread dept/t

Illustration of loosest condition for class 20 threads

free fit, one-fourth inch,

Fig. 9. -Illustration of tightest condition for class one-fourth inch, 20 threads

?, free fit,
FITS, ALLOWANCES, AND TOLERANCES 33

(c) Maximum screw basic.6—The major diameter and pitch diameter of the maximum screw of a given pitch and diameter correspond

to the basic dimensions, as specified in tables of thread series given

herein, which are computed from the basic major diameter of the

thread.

(d) Allowance and tolerance values.—Allowances and tolerances are

-specified in Table 4. Table 4.

Class 2, free fit, tolerances for screws and nuts (no allowances)

Threads per inch Allowances

Pitch diameter

tolerances !

Lead errors consuming

one-half

of pitch- diameter

tolerances 2

Errors in

half-angle consuming

one-half

of pitch- diameter

tolerances

80

7264

56

48

44

40

3632

28

24

20

1816

14

1312

1110 (American National coarse)

10 (American National fine) — . 9

8 (American National coarse)

.

8 (American National fine)

766

V/i 43H

Inch

0.0000

.0000

.0000

.0000 .0000

.0000

.0000

.0000

.0000 .0000 .0000

.0000

.0000 .0000

.0000

.0000 .0000

.0000

.0000 .0000

.0000

.0000

.0000 .0000

.0000

.0000 .0000

.0000 .0000

Inch

0. 0017 .0018

.0019 .0020

.0022

.0023

.0024

.0025 .0027

.0031

.0033

.0036

.0041 .0045

.0049 .0052

.0056

.0059 .0064

.0100 .0070

.0076 .0110

.0085 .0101

.0116 .0127

.0140 .0157

Inch

0.0005

.0005

.0005

.0006

.0006

.0007

.0007

.0007 .0008

.0009 .0010

.0010

.0012

.0013 .0014

.0015

.0016

.0017 .0018

.0029

.0020

.0022

.0032

.0025

.0029 .0033

.0037 .0040 .0045

Beg. Min.

2 36

2 28

2 19 2 8

2 1

1 The tolerances specified for pitch diameter include all errors of pitch diameter, lead, and angle. The full

tolerance can not, therefore, be used on pitch diameter unless the lead and angle of the thread are perfect. Columns

i and 5 give, for information, the errors in lead (per length of thread engaged) and in angle, each of which can be compensated for by half the tolerance on the pitch diameter given in column S. If lead and angle errors both exist

to the amount tabulated, the pitch diameter of a bolt, for example, must be reduced by the full tolerance or it will

not enter a basic nut or gage.

1 Between any two threads not farther apart than the length of engagement.

3. Class 3, Medium Fit.—(a) Definition.—The medium-fit class

is intended to apply to the manufacture of the higher grade of threaded

parts which are to assemble nearly or entirely with the fingers and

must have the minimum amount of shake or play between the threaded

* The maximum minor diameter of the screw is above the basic minor diameter, as shown in Figure 7.
34 NATIONAL SCREW THREAD COMMISSION

members. It is the same in every particular as class 2, free fit, except

that the tolerances are smaller.

(b) Minimum nut basic.—The pitch diameter of the minimum nut

of a given diameter and pitch corresponds to the basic pitch diameter, as specified in tables of thread series given herein, which is computed from the basic major diameter of the thread.

(c) Maximum screw basic.7—The major diameter and pitch diameter

of the maximum screw of a given pitch and diameter correspond to the basic dimensions, as specified in tables of thread series given

herein, which are computed from the basic major diameter of the

thread.

(d) Allowance and tolerance values.—Allowances and tolerances are specified in Table 5. Table 5.

Class 3, medium fit, tolerances for screws and nuts (no allowances)

Threads per inch Allowances

Pitch- diameter

tolerances °

Lead errors consuming

one-half

of pitch- diameter

tolerances h

Errors in

half-angle consuming

one-half

of pitch- diameter

tolerances

80

72

645648

4440

36

32. 28.. 2420

18

16

14

1312

11 ... 10 (American National coarse)

10 (American National fine)... 9

8 (American National coarse)

.

8 (American National fine) 7

6

54M -

43MInch

0.0000

.0000

.0000

.0000

.0000

.0000

.0000

.0000 .0000 .0000

.0000

.0000

.0000

.0000 .0000

.0000

.0000

.0000

.0000 .0000

.0000

.0000 .0000

.0000

.0000

.0000 .0000

.0000

.0000

Inch

0.0013

.0013

.0014 .0015

.0016

.0016

.0017 .0018

.0019 .0022

.0024

.0026

.0030

.0032

.0036 .0037

.0040

.0042

.0045 .0084

.0049

.0054

.0092

.0059

.0071 .0082

.0089 .0097

.0107

Inch

0.0004

.0004

.0004

.0004 .0005

.0005

.0005 .0005

.0005 .0006

.0007

.0009

.0010

.0011 .0012

.0012

.0013

.0024

.0014

.0016

.0027

.0017

.0020

.0024

.0026

.0028

.0031

Beg. Min.

59

47

° The tolerances specified for pitch diameter include all errors of pitch diameter, lead, and angle. Tht full tolerance can not, therefore, be wed on pitch diameter unless the lead and angle of the thread are perfect. Columns

4 and 5 give, for information, the errors in lead (per length of thread engaged) and in angle, each of which can be compensated for by half the tolerance on the pitch diameter given in column 3. If lead and angle errors both exist to the amount tabulated, the pitch diameter of a bolt, for example, must be reduced by the full tolerance or it will not enter a basic nut or gage.

b Between any two threads not farther apart than the length of engagement.

7 The maximum minor diameter of the screw is above the basic minor diameter, as shown in Figure 10.
FITS, ALLOWANCES, AND TOLERANCES 35

h - bas/c

DEPTHJ°/eay/ L/nE Shows

Fig. 10.

Illustration of tolerances and crest clearances for class St medium fit
6 NATIONAL SCREW THREAD COMMISSION

NOTE: DOTTED LIN£ SHOWS BASIC SIZE

T/ON

E-pi tch diame ter- K- minor diameter

h *.032&=baste thread depth

Fig.

SCREW NUT

11.

Illustration of loosest condition for class 8, medium fit, one-fourth

inch, 20 threads

Fig. 12.-—Illustration of tightest condition for class 8, medium

fit, one-fourth inch, 20 threads

NOTATION D—major diameter E=pitch diameter K—minor diameter

h =0.0325= basic thread depth
FITS, ALLOWANCES, AND TOLERANCES 37

4. Class 4, Close Fit.—(a) Definition.—The close-fit class is in- tended for threaded work of the finest commercial quality where very

little shake or play is desirable

may be necessary for assembly.

-ipand where a screw driver or wrench

In the manufacture of screw-thread

A = &AS/C TH&SAD

/¥£AYrLfN£ Shows

pi*

Fig. 13.Illustration of tolerances, allowance (interference), and crest clearances for class 4, close fit products belonging in this class it will be necessary to use precision

tools, selected gages, and other refinements. This quality of work

should, therefore, be used only in cases where requirements of the

mechanism being produced are exacting, or where special conditions
38 NATIONAL SCREW THREAD COMMISSION

require screws having a precision fit. In order to secure the fit desired

it may be necessary in some cases to select the parts when the product

is being assembled.

(b) Minimum nut basic.—The pitch diameter of the minimum nut

of a given diameter and pitch corresponds to the basic pitch diameter,

as specified in tables of thread series given herein, which is computed

from the basic major diameter of the thread.

(c) Maximum screw above basic.—The pitch diameter of the maximum screw of a given diameter and pitch is above the basic dimensions

as specified in tables of thread seiies given herein, which are computed from the basic major diameter of the thread, by the amount of the allowance (interference) specified in Table 6. (d) Allowance and tolerance values.—Allowances and tolerances are

specified in Table 6. Table 6.

Class 4y close fit, allowances and tolerances for screws and nuts

Threads per inch

10 (American National coarse)

.

10 (American National fine)...

Interfer- ences or negative allowances

8 (American National coarse)

.

8 (American National fine)...

5... 4... 3^-

lnch

0. 0001 .0001

.0001 .0002

.0002 .0002

.0002

.0002

.0002 .0002

.0003

.0003

.0003

.0004

.0004

.0004

.0005

.0005 .0005

.0006 .0006

.0007

.0007

.0008

.0010 .con

.0013

.0016

Pitch- diameter

tolerances i

Inch

0. 0006 .0007

.0007

.0007 .0008

.0008

.0009

.0009

.0010

.0011 .0012

.0013 .0015

.0016

.0018

.0019

.0020

.0021 .0023

.0042

.0024 .0027

.0046

.0030

.0041 .0044 .0048

.0053

Lead errors consuming

one-half of pitch- diameter

tolerances 1

Inch

0. 0002

.0002 .0002

.0002 .0002

.0002

.0003

.0003

.0003 .0003

.0003

.0004

.0004

.0005 .0005 .0005

.0006

.0006

.0007

.0012

.0007

.0008

.0013 .0009

.0010 .0012

.0013

.0014 .0015

Errors in half-angle consuming

one-half of pitch- diameter

tolerances

Deg. Min.

55

i The tolerances specified for pitch diameter include all errors of pitch diameter, lead, and angle. The full tolerance can not, therefore, be used on pitch diameter unless the lead and angle ofthe thread are perfect. Columns

4 and 5 give, for information, the errors in lead (per length of thread engaged) and in angle, each of which can be compensated for by half the tolerance on the pitch diameter given in column S. If lead and angle errors both exist to the amount tabulated, the pitch diameter of a bolt, for example, must be reduced by the full tolerance or it will not enter a basic nut or gage.

3 Between any two threads not farther apart than the length of engagement.
FITS, ALLOWANCES, AND TOLERANCES 39

\ / * 1 SCREW NUT

Fig. 14.Illustration of loosest condition for class 4, dose fit, one-fourth inch, 20 threads

Fig. 15.Illustration of tightest condition for class 4, close fit, one-fourth inch, 20 threads

NOTATION D=major diameter B=pitch diameter K=*minor diameter

h =0.0325 -basic thread depth
NATIONAL SCREW THREAD COMMISSION
DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS 41

PITCH —INCH

Fig. NUMBER Or THREADS PER INCH 17.

Limits for minor diameter of nut, American National coarse and

thread series

4. TABLES OF DIMENSIONS

The limiting dimensions of American National coarse and American

National fine threads, to be made to the tolerances and allowances

determining the various classes of fit, as herein established, are here

tabulated.
Ill

NATIONAL SCREW THREAD COMMISSION

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44 NATIONAL SCREW THREAD COMMISSION

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NATIONAL SCREW THREAD COMMISSION

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ii

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JI
DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS 47

.2 si

060

.073 .086 099 .112 ,125]138 164 190 216 2500 3125 3750 4375 5000 5625 6250 7500 8750 0000 1250 2500 5000 7500 0000 2500 5000 7500 0000

03 03 H «a|

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diameter,

minimum

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48 NATIONAL SCREW THREAD COMMISSION

ill F

ran tmu tISSt Bill Hill till

1

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DIMENSIONAL LIMITS OF FASTENING=SCREW THREADS 49

Ifj

1

a

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mi

1

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urn inii mil urn inn in

mil mn inii 11111 iim mi

11111 mil iim urn inii mi

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mil iim iim urn iim mi

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50 NATIONAL SCREW THREAD COMMISSION

io ^ o »o o § 338 Is!1

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pit<

pitch d

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DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS

!?SS3 8

m © ©

HNO) rH i-l O <N O rH t-H 00

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.1900 .1541 .1449 .0092 .1629 .1675 .0046 .1662 .0033 .1653 .0024 .1641 .0012

.1640 .1378 .1302 .0076 $ .1475 .0038 .1464 .0027 .1456 .0019 .1447 .0010

.1380 .1118 .1042 .0076 .1215 .0038 .1204 .0027 .1196 .0019 .1187 .0010

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NATIONAL SCREW THREAD COMMISSION

1

l

1

5 Si 111! ill III 11 III III 111 III

fill 111 ill 11 111 III III li!

8 J!!! Ill III 1! Ill 111 111 ill

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BOLTS

AND

SCREWS

(Max..

Class

1.

maior

diameter

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Classes

2,

3,

and

4,

major

diameter

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2,

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diameter

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parts

of

l^n*"

unfinished,

hot-rolled

material

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'

Class

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minor

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3,

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4,

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fit,

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DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS

cot>.o lb. rHb- t^CO IH NH r-IC= O 00O 000

I III I II II 11 II

CO «N<N ' <N CNi * <N ' N ' <N

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NATIONAL SCREW THREAD COMMISSION

I 111 111 il III 111 ill ill

32

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n

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06^"5 **< ©© CO 00 co cm cm 8 8 88 88 88

O COCO© 00 i-H CO ©i-H O —< O CO i-H Tf( C! CO

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56 NATIONAL SCREW THREAD COMMISSION

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3°-8 i8 38 38 3<

28

S8 £8

88

.8750 .8062 .7977 .0085 CO8QO.8356 .0070 .

8335

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7126

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NATIONAL SCREW THREAD COMMISSION

III ill ii ill ii! ili ill

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igl 111 I

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60 NATIONAL SCREW THREAD COMMISSION

5. GAGES

The art of measuring screw threads has developed very rapidly

during the past few years. This development still continues, so that

it would be inadvisable to attempt to specify any definite method as standard for this purpose. The objects are to establish the fundamentals of this subject, and to point oat practices now successfully

used.

(a) FUNDAMENTALS

1. Object of Gaging.—The final results sought by gaging are to secure interchangeability; that is, the assembly of mating parts without selection or fitting of one part to another, and to insure that the

product conforms to the specified dimensions within the limits of variation establishing the closest and loosest conditions of fit permissible in any given case, as provided for in the foregoing specifications.

This requires the use of gages representing the limit of maximum

metal, known as "go" gages, which control the minimum looseness or maximum tightness in the fit of mating parts, and which accordingly

control interchangeability; and the use of gages representing the

limit of minimum metal, known as "not go" gages, which limit the

amount of looseness between mating parts, and thus control in large measure the proper functioning of the parts.

Gaging should be as much employed to prevent unsatisfactory

parts from being produced as to sort out the correct from the incor- rect parts.

2. Purpose of "Go" and "Not Go" Gages.—The "go" gages

control the extent of the tolerance in the direction of the limit of maximum metal, and represent the maximum limit of the internal

member and the minimum limit of the external member. To pass

inspection, parts must be acceptable to proper "go" gages, and such

mating parts will always assemble. Successful interchangeable manufacturing has been carried on for many years with the use of "go"

gages only.

"Not go" gages control the extent of the tolerance in the direction

of the limit of minimum metal, and represent the minimum limit of the internal member and the maximum limit of the external member.

To be acceptable, parts must not enter or be entered by proper

"not go" gages. It is general practice to permit "not go" thread

gages to enter or be entered by the product not more than 1 y% turns. There is a broad, general principle in regard to limit gages which

should be kept in mind; a "go" gage should check simultaneously as many elements as possible, a "not go" gage, to be effective, can check

but one element. By effective inspection is meant assurance that

specified requirements in regard to size are not exceeded. A "not

go" thread gage made to check only the pitch diameter is usually

sufficient for practical purposes.
FUNDAMENTALS OF GAGING SCREW THREADS 61

3. Gage Classification.—The limiting dimensions of the threaded

parts to be produced must be represented in: (a) Gages used in checking the product as it is machined, known as " working gages";

(b) gages for use in the acceptance of the product, known as

'

' inspection

gages"; and (c) gages used to determine the accuracy of the two pre- ceding classes of gages, known as "master gages."

4. Gages Used to Measure the Product.—The gages used to

' check the product may be divided into two general types: "Mechanical" and "optical." Both types, however, are controlled by the master gages. Most of the product accepted by one type of gaging with

a correct gage will be accepted by the other. It should be pointed

out, however, that those parts which are near either rejection point

may be accepted by one system and rejected by the other.

(a) Mechanical gages*—Mechanical gages ordinarily comprise the

inspection and working gages as above defined, and these two classes are generally of the same design. The dimensions of inspection gages

are such that they represent very nearly the extreme limits of the part.

It is recommended that, when successive inspections are required, the

working gages, either by design or selection, be of such dimensions that

they are inside the limits of the gages used in succeeding inspections.

(b) Optical gages.—When gages of the optical type are employed,

the elements of wear and "feel" are not involved, hence no differ- ence in size between inspection and working gages is necessary, but

is desirable.

i 5. Gages for Reference.—(a) Master gage.—The master gage

1 is a thread-plug gage which represents the physical dimensions of the

nominal or basic size of the part. It clearly establishes the minimum

i size of the threaded hole and the maximum size of the screw at the

point at which interference between mating parts begins. A master

. gage shall be accompanied by a record of its measurement. In case

1 of question, the deviations of this gage from the basic size shall be

ascertained by the Bureau of Standards at Washington, D. C.

L (b) Setting gage (check gage).—A setting gage is a thread-plug gage

i to which adjustable thread-ring gages and other thread comparators

; i are adjusted for size. In adjusting thread-ring gages to size, the set- ting plug gage should control the pitch diameter, and it will do so if

[; proper clearance is provided at the major diameter of the ring gage, and if the minor diameter is within the specified limits. The ring

i gage should be given further inspection as to these points. The minor

\ diameter may be inspected by means of "go" and "not go" plain

plug gages, and the major diameter by optical examination of a

sulphur-graphite, plaster-of-Paris, or other suitable cast of the thread.

I, 6. Direction of Tolerances on Gages.—The sizes for limit

• gages shall never be outside oj the limits specified jor the product. All

8 Recommendations as to the design and construction of mechanical gages are given in Appendix 7.
\ 62 NATIONAL SCREW THREAD COMMISSION

variations in the gages, whatever their cause or purpose, shall hring these gages within these extreme limits. Thus, a gage which represents a irdnimum limit may be larger, but never smaller, than the minimum

size specified for the part, while the gage which represents a maximum

limit may be smaller, but never larger, than the maximum size specified

for the part.

7. Thread Form of Thread Plug and Ring Gages.—The minor

diameter of the "go" thread ring gage is the same as the minimum

minor diameter of the nut or tapped hole with a minus gage tolerance.

The minor diameter of the "not go" ring gage is the minimum minor

diameter of the nut plus at least 0.0002 inch, with a plus gage tolerance.

Also the maximum major diameter of the "not go" thread plug gage

is at least 0.0002 inch less than the basic major diameter, with a minus

gage tolerance. (See fig. 18.)

A relief is provided at the root of the "go " thread plug or ring gage, the width of which is not greater than one-eighth of the pitch. Also a relief is provided at the root of the "not go" thread plug or ring

gage, the width of which is approximately one-fourth of the pitch.

Thus contact of the "not go" thread gage on the sides of the

threads, rather than at the corners of the crest and root, is assured.

8. Temperature at Which Gages Shall be Standard.—The

nominal dimensions of gages and product shall he correct at a temperature of 68° F. {20° €.). As gages and products are ordinarily checked at room temperature, whatever it may happen to be, it is desirable that the thermal

coefficient of expansion of gages be the same as that of the product on which they are used. Inasmuch as the majority of threaded

products consist of iron and steel, and as screw-thread gages are ordinarily made of hardened steel, because of its high wear-resisting

qualities, this condition is ordinarily fulfilled without giving'it specia

attention.

9. Measuring Pressure for Three-Wire Measurements.9—In

measuring the pitch diameter of hardened screw-thread gages by means of wires, and in measuring the wires themselves, the same

contact pressure should be used. A contact pressure of 8 ounces is recommended for pitches finer than 20 threads per inch, and of not more than 3 pounds for 20 threads per inch and coarser. It is also recommended as standard practice that wires be measured between

a flat contact and a cylindrical contact 0.750 inch in diameter.

(b) SPECIFICATIONS FOR GAGES

The following specifications are for the purpose of establishing

definite limits for thread gages rather than for the purpose of specifying the gages required for the various inspection operations:

Methods of measuring pitch diameter of screw thread gages are described in Appendix 2 p. 184.
Gage tolerances 63

1. Classification of Gages, and Gage Tolerances.—Screwthread gages are classified according to accuracy into classes X, Y,

and Z, the class X being the most accurate. The tolerance limits on classes Y and Z "go" gages are placed inside of the extreme

product limits to provide allowance for wear of the gages. The tol- erances on all "not go" gages, however, are applied from the ex- treme product limit as the starting point, as no allowance for wear is necessary. The selection of gages from among these classes for use

in the inspection of threaded product depends entirely upon the

specifications for the product. For example, in the production of

parts to class 4, close fit specifications, class X -gages may be re- quired for all purposes. On the other hand, for parts made to class 1, loose fit specifications, class Z gages may be sufficiently accurate

for all purposes.

(a) Master gages.—No fixed tolerances are specified for master

gages. These should be made to the basic size as accurately as possible and be within the tolerances specified for class X gages. The

variations from basic size shall be plus. Each master gage shall be

marked with an identification number or symbol, and be accompanied by a record of its measurement on major diameter, pitch

diameter, lead, and angle. In case of question, the deviations of

such gages from the exact standard shall be ascertained by the

Bureau of Standards at Washington, D. C.

(5) Class X gorges.—Class X gages should be suitable for inspection and setting gages for all classes of fits. They may also be neces- sary for working gages for the class 4 fit. The tolerances on these

gages are given in Table 18. In all cases the tolerances shall be such

that the gage does not fall outside of the component tolerances. For

example, if a thread-plug gage is used as the "go" gage for checking a tapped hole, it can be larger, but not smaller than the minimum size specified. On the other hand, if a thread-plug gage is used

as the "go" setting plug for thread-ring gages or for optical or

other comparators, it can be smaller, but never larger than the

maximum size of the screw. Class X tolerances, as given in Table 18, are specified for all "not

go" gages.

(c) Class Y gages.—Class Y gages should be suitable for inspection gages for classes 1, 2, and 3 fits. They may also be desired as working gages for classes 2 and 3 fits. The tolerances on these

gages are given in Table 19.

(d) Class Z gages.—Class Z gages should be suitable for working

gages for class 1, loose fit. The tolerances on these gages are given

in Table 20.

(e) Wear on gages.—"Go" gages may be permitted to wear to

the extreme product limits. It is desirable, however, that working
64 NATIONAL SCREW THREAD COMMISSION

and inspection gages be so selected that the dimensions of the working gages are inside of the limiting dimensions represented by the

inspection gages, in order that all parts passed by the working gage

will be accepted by the inspection gage. As to wear on "not go" gages, it is purely a question of economy

as to when the "not go" gage should be discarded. Continued use reduces the available working tolerance on the product, and the 1 resulting loss must be balanced against the cost of a new gage.

(f) Tolerances on lead.—The tolerances on lead given in Tables 18

to 20, inclusive, are specified as an allowable variation between any

two threads not farther apart than the length of engagement of th

assembled threaded product. When this length of engagement is equal to the diameter, the permissible progressive lead errors per

inch may be determined by dividing these lead tolerances by the

corresponding diameters.

(g) Tolerances on angle of thread.—The tolerances on angle of

thread, as specified in Tables 18 to 20, inclusive, for the various

pitches, are tolerances on one-half of the included angle. This

insures that the bisector of the included angle will be perpendicular

to the axis of the thread within proper limits. The equivalent

deviation from the true thread form caused by such irregularities as convex or concave sides of thread, rounded crests, or slight projections on the thread form, should not exceed the tolerances per- mitted on angle of thread.

2. Tolerances for Plain Gages.—For plain plug gages, plain

ring gages, and plain snap gages required for measuring diameters

of screw-thread work, the gage tolerances specified in Table 18 should

be used. Attention is directed to the fact that the tolerances on

thread diameters vary in accordance with the number of threads per

inch. In manufacturing a plain plug, ring, or snap gage, in the

absence of information as to the number of threads per inch of the screw to be made, or for gage dimensions other than thread diameters, the tolerances for plain gap*es given in Table 21 may be used.

This table contains recommended tolerances for classes X, Y, and Z

gages, which have been tentatively adopted by the A. S. A. Sectional Committee on the Standardization of Plain Limit Gages for General Engineering Work.

3. Recommended Gage Practice.—There are given in Table 17

the recommended uses for the foregoing classes of gages. Tables 22,

23, 24, and 25 give limiting dimensions of gages of the several classi- fications for the American National coarse and American National

fine thread series.
GAGE TOLERANCES

Table 17.

Recommended uses for classes X, Y, and Z gages 65

PIqqc nf fit Inspection ^3*^e

1 2 3 i

Class 1, loose fit Class X. Class Y Class Z. Class Y.

Do.

Class X. .

Class 2, free fit do- do

Class 3, medium fit — do Class X

Class 4, close fit do do Table 18. Tolerances for class X "go" thread gages and all "not go" thread gages

Threads per inch

Tolerance on pitch diameter i From— To—

Tolerance

in lead J Tolerance on half angle of thread

Tolerance on major or minor diameters 1 From

ToInch

0. 0000

.0000

.0000

.0000 .0000

.0000

.0000

.0000

.0000 .0000

.0000

.0000

.0000 .0000

.0000 .0000

.0000

.0000

.0000 .0000

.0000

.0000 .0000

.0000

.0000 .0000

.0000

Inch

0. 0002 .0002

.0002 .0002

.0002

.0002

.0002 .0002

.0003

.0003 .0003

.0003

.0003 .0003 .0003

.0003

.0003

.0003 .0003 .0003

.0004

.0004 .0004

.0004

.0004 .0004 .0004

Inch ±

0.0002

.0002 .0002

.0002

.0002 .0002

.0002

.0002

.0003 .0003

.0003

.0003 .0003

.0003 .0003

.0003 .0003

.0003 .0003

.0003

.0004 .0004 .0004

.0004

.0004

.0004 .0004

Beg. Min.

=fc 30 Inch

0. 0000

.0000

.0000

.0000

.0000

.0000

.0000

.0000

.0000

.0000 .0000

.0000

.0000

.0000 .0000

.0000

.0000

.0000 .0000

.0000

.0000 .0000

.0000

.0000

.0000

.0000

.0000

Inch

0. 0003

.0003

.0004 .0004

.0004

.0004

.0004

.0004 .0004

.0005 .0005

.0005 .0005

.0006

.0006

.0006 .0006

.0006 .0006

.0007

.0007

.0007

.0008

.0008

.0008

1 On "go" plugs the tolerance is plus, and on "go" rings the tolerance is minus. On "not go" plugs

the tolerance is minus, and on "not go" rings the tolerance is plus.

1 Allowable variation in lead between any 2 threads not farther apart than the standard length of engagement, which is equal to the basic major diameter. It is suggested that, in case of question between the manufacturer

and purchaser of threaded products in regard to their size, if the

manufacturer produces limit gages which do not measure outside of the specified limits for the threaded components and which pass the

parts in question, they be accepted as meeting the specifications for

size. In case the dimensions of the gages are questioned, their

sizes shall be determined by a disinterested third party, preferably
66 NATIONAL SCREW THREAD COMMISSION

the Bureau of Standards at Washington, D. C, which maintains a department for this service.

4. Marking of Gages.—Each gage shall be plainly and permanently marked, for identification, with the diameter, pitch, thread

series, and class of fit. See Section II, division 2, " Symbols."

For example: A 1-inch, 8-pitch gage of the American National

coarse thread series, class 2, free fit, shall be marked 1"—8—NC—2. A 1-inch, 14-pitch gage of the American National fine thread series, class 3, medium fit, shall be marked 1"—14—NF—3. Table 19.

Tolerances for class Y "go" thread gages

Threads per inch

Tolerance on pitch diameter 1 TolcrsncG

in ls&d ^ Tolerance on half angle of thread

Tolerance on major or minor diameters 1 From— To— From

To—

A 3 4 5 _

6 7

Inch Beg. Mm. Inch Inch

_i_ ±

80 0. 0001 0. 0003 0. 0002 45 0.0000 0. 0003

72 .0001 .0003 !0002 45 .0000 .0003

64 .0001 .0004 .0002 45 .0000 .0004

56 .0001 .0004 .0002 45 .0000 .0004

48 .0001 .0004 .0002 45 .0000 .0004

44 .0001 .0004 .0002 30 .0000 .0004

40 .0001 .0004 .0002 30 .0000 .0004

36 .0001 .0004 .0002 30 .0000 .0004

32 .0001 .0004 .0003 20 .0000 .0004

28 .0002 .0005 .0003 20 .0000 .0005

24 .0002 .0005 .0003 20 .0000 .0005

20 .0002 .0005 .0003 20 .0000 .0005

18 .0002 .0005 .0003 15 .0000 .0005

16 .0002 .0006 .0003 15 .0000 .0006

14 .0002 .0006 .0003 15 .0000 .0006

13 .0002 .0006 .0003 15 .0000 .0006

12 .0002 .0006 .0003 10 .0000 .0006

11 .0002 .0006 .0003 10 .0000 .0006

10 .0002 .0006 .0003 10 .0000 .0006

9 .0002 .0007 .0003 10 .0000 .0007

8 .0002 .0007 .0004 5 .0000 .0007

7 .0002 .0007 .0004 5 .0000 .0007

6 .0003 .0008 .0004 5 .0000 .0008

5 .0003 .0008 .0004 5 .0000 .0008 4^- .0003 .0008 .0004 5 .0000 .0008 4 .0003 .0009 .0004 5 .0000 .0009

.0003 .0009 .0004 5 .0000 .0009

i On "go" plugs the tolerance is plus and on "go" rings the tolerance is minus.

* Allowable variation in lead between any two threads not farther apart than the standard length of engagement, which is equal to the basic major diameter.
GAGE TOLERANCES 67

Table 20.

Tolerances for class Z "go" thread gages

Threads per inch

Tolerance on pitch . diameter 1

. Tolerance

in lead 2 Tolerance on half angle of thread

Tolerance on major or minor diameters

»

From— To— From

To—

1 2 3 4 5 6 7

Inch Inch Inch Deg. Min. Inch Inch ± ±

80 0.0002 0.0006 0. 0002 45 0. 0000 0. 0003

72 . 0002 . 0006 .'0002 45 0000 0003

64 !0002 !0006 .0002 o 45 !oooo !0004

56 . 0002 . 0007 .0002 45 0000 0004

48 !0002 !(X)07 .0002 • 45 !oooo !0004

44 .0002 .0007 .0002 30 .0000 .0004

40 . 0002 . 0007 .0002 30 .0000 .0004

36 .0003 .0008 .0002 o 30 .0000 .0004

32 .0003 .0008 .0003 20 .0000 .0004

28 .0003 .0008 .0003 20 .0000 .0005

24 . 0003 .0009 .0003 20 .0000 .0005

20 .0003 .0009 .0003 20 .0000 .0005

18 .0004 .0010 .0004 15 .0000 .0005

16 .0004 .0010 .0004 15 0000 0006

14 .0004 .0010 . 0004 15 .0000 .0006

13 .0004 .0011 .0004 15 .0000 .0006

.0004 .0011 .0004 10 .0000 .0006

11 .0004 .0011 .0004 10 .0000 .0006

10 .0005 .0012 .0004 10 .0000 .0006

9 .0005 .0012 .0004 10 .0000 .0007

8 .0006 .0013 .0005 5 .0000 .0007

7 .0006 .0013 .0005 5 .0000 .0007

6 .0006 .0014 .0005 5 .0000 .0008

5 .0007 .0015 .0005 5 .0000 .0008 .0007 .0015 .0005 5 .0000 .0008 4 .0007 .0016 .0005 5 .0000 .0009 m~ .0007 .0016 .0005 5 .0000 .0009

1 On "go" plugs the tolerance is plus, and on "go" rings the tolerance is minus.

2 Allowable variation in lead between any two threads not farther apart than the standard length of engagement, which is equal to the basic major diameter. Table 21.

Tolerances for plain gages 1

Size of gage in inches Class X 2 Class Y Class Z From

To— From— To— From

To—

2 3 I 5 6 7

to 1, inclusive

1 to 3, inclusive

Inch

0. 0000 .0000

Inch

0.0001 .0002

Inch

0. 0001 .0001

Inch

0. 0002

.0003

Inch

0. 0002

.0003

Inch

0. 0003 .0005

1 On "go" plugs the tolerance is plus, and on "go" rings the tolerance is minus. On "not go" plugs

the tolerance is minus, and on "not go" rings the tolerance is plus.

s All "not go" gages are made to class X tolerances.
NATIONAL SCREW THREAD COMMISSION

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78 NATIONAL SCREW THREAD COMMISSION

SECTION IV. SCREW THREADS OF SPECIAL DIAMETERS,

PITCHES, AND LENGTHS OF ENGAGEMENT

The tolerances specified in Section III of this report apply in general

to bolts, nuts, and tapped holes of standard pitches and diameters.

They are based on the pitch of the thread and a length of engagement

equal to the basic major diameter, but are used for lengths of engagement up to 1 3^2 diameters.

M/nimum or "s o "Plug Gage Maximum or'not go'Plug Sage

Max/mum or "c o'Ring Ga ge M/n/mum or'not go'Ring Ga ge

A/OTEl- "NOT GO" <3A6£S CHECK PJTCH Q/AME7E/i ONLY

Fig. 18.

Thread form of "go" and "not go" thread plug and

ring

In addition to the foregoing threaded components, there are large

quantities of threaded parts produced, such as hub and radiator caps

in the automotive industry, threaded collars on machine tools, etc., where the diameters are larger, the pitches finer, and the lengths of engagement shorter than for bolt and nut practice. The following

specifications have been adopted for such threaded parts, and the

tolerances are based on the diameter, pitch, and length of engagement

of the components.
SPECIAL THREADS 79

1. FORM OF THREAD

The American National form of thread profile as specified in

Section III shall be used.

2. THREAD SERIES

It is recommended that one of the following pitches be selected

whenever it is necessary to use a screw thread of special diameter

) and pitch: 4, 6, 8, 10, 12, 14, 16, 18, 20, 24, 28, 32, 36, 40, 48, 56, 64

threads per inch.

Basic thread data for these pitches are given in Table 26. The

- use of 12 threads per inch, wherever possible, is recommended for

all applications requiring special threads. This pitch is very con- venient for a variety of miscellaneous work in machine construction,

as for thin nuts on shafts and sleeves, on threaded studs, etc. It is the coarsest pitch, for a thread of basic depth, which will permit a threaded collar which screws onto a threaded shoulder to slip over a

shaft, the difference in diameter between shoulder and shaft being

one-eighth inch.

In Section XD there are given the limiting dimensions for 12 pitch

threads of the following sizes: %, Yu, %, %, %, %, %, %, 1, 1#6 , lft He, 1%, 1%6, 1%, 13ft 1%, 2, 2% 2%, 2%, and 3 inches. Sizes up

to an including 1% inches are widely used in railroad practice and die- head chasers for these sizes are stocked by manufacturers.

3. CLASSIFICATION AND TOLERANCES

There are established herein for general use four classes of screw- thread fits, which are named and numbered to correspond to the

regular classification of fits given in Section III. These four classes,

together with the accompanying specifications, are intended to insure a uniform practice for screw threads not included in the American

National coarse or fine thread series. Table 26.

Thread data for recommended pitches for special threads

Threads per inch Pitch

P

Depth of thread

h

Basic width

of flat

P/8

Minimum

width of

flat at major

diameter

of nut

p/24

2 3 4 5

64. Inch

0. 01562

. 01786

.02083

. 02500

. 02778

. 03125

. 03571

. 04167

.05000

.05556

.06250

. 07143

.08333 .10000

. 12500

. 16667 .25000

Inch

0. 01015

.01160

. 01353

. 01624 .01804

. 02030

. 02320

. 02706

.03248

. 03608

. 04059

.04639

. 05413

.06495

. 08119

. 10825

. 16238

Inch

0. 00195

.00223

. 00260

. 00312

. 00347

.00391 .00446

.00521 .00625 .00694

. 00781

. 00893 .01042 .01250

.01562

.02083

. 03125

Inch

0. 00065

.00074

. 00087

.00104

. 00116

. 00130

.00149

.00174

.00208

.00231

. 00260

. 00298

. 00347

. 00417

.00521 .00694 .01042

564840

36

32

28

24

20

18

16 14„_

12

108

6.4
80 NATIONAL SCREW THREAD COMMISSION

It is not the intention of the commission arbitrarily to place a

general class or grade of work in a specific class of fit. Each manufacturer and user of screw threads is free to select the class of fit best

adapted to his particular needs.

(a) GENERAL SPECIFICATIONS The following general specifications apply to all cjasses of fit specified for screw threads of special diameters, pitches, and lengths

of engagement.

1. Uniform Minimum Nut.—The pitch diameter of the minimum

threaded hole or nut corresponds to the basic size. 10 2. Tolerances.11—(a) The tolerances specified represent the

extreme variations allowed on the product.

(&) The tolerance on the nut is plus, and is applied from the basic

size to above basic size.

(c) The tolerance on the screw is minus, and is applied from the

maximum screw size to below the maximum screw size. (d) The pitch diameter tolerances for a screw and nut of a given

class of fit are the same.

1(e) Pitch diameter tolerances include all errors of pitch diameter,

lead, and angle. The full tolerance can not, therefore, be used on

pitch diameter unless the lead and angle of the thread are perfect.

(J) The pitch diameter tolerances are obtained by adding three

values, or increments; one dependent upon the basic major diameter,

another upon the length of engagement, and the third upon the pitch

of the thread. These increments are based on formulas given in

Appendix 1. However, where tolerance values so obtained exceed

those given in Section III for corresponding pitches of the American

National coarse or fine thread series, and for any diameters equal to or less than these standard sizes and lengths of engagement equal to or less than one diameter, the tolerances given in Section III are used. (See rules for using tolerance tables on p. 83.)

jig) The tolerances on the major diameters of the screws and minor

diameters of the nuts are based on the pitch of the thread, as these

control the depth of engagement; they are, therefore, based on the

pitch alone.

(h) The minimum minor diameter of a screw of a given pitch is such as to result in a basic flat (J^ Xp) at the root when the pitch

diameter of the screw is at its minimum value. When the maximum

screw is basic, the minimum minor diameter of the screw will be below the basic minor diameter by the amount of the specified pitch

diameter tolerance.

10 Special cases will arise/however, when a class 1 thread is required on finished drawn tubing with thin

walls, and in such cases the allowance should be made on the nut.

11 Recommendations and explanations regarding the application of tolerances are given in Appendix 1, page 181 i
SPECIAL THREADS 81

(i) The maximum minor diameter of a screw of a given pitch may

be such as results from the use of a worn or rounded threading tool,

when the pitch diameter is at its maximum value. In no case, however, should the form of the screw, as results from tool wear, be such

as to cause the screw to be rejected on the maximum minor diameter

by a "go" ring gage, the minor diameter of which is equal to the

minimum minor diameter of the nut.

(J) The maximum major diameter of the nut of a given pitch is such as to result in a flat equal to one-third of the basic flat (%iXp)

when the pitch diameter of the nut is at its maximum value. When

the mininum nut is basic, its maximum major diameter will be above

the basic major diameter by the amount of the specified pitch diameter

tolerance plus two-ninths of the basic thread depth.

(k) The nominal minimum major diameter of a nut is the basic

major diameter. In no case, however, should the minimum major

diameter of the nut, as results from a worn tap or cutting tool, be such

as to cause the nut to be rejected on the minimum major diameter

by a "go" plug gage made to the standard form at the crest.

(I) The tolerance on minor diameter of a nut of a given pitch is one-sixth of the basic thread depth regardless of the class of fit.

12

(b) CLASSIFICATION OF FITS

1. Class 1, Loose Fit.—This class is intended to cover the manufacture of threaded parts where quick and easy assembly is necessary

and a considerable amount of shake or play is not objectionable.

This class is made with an allowance on the screw, so as to permit

ready assembly, even when the threads are slightly bruised or dirty,

in conformity with the practice in Section III. 13 Tables 27 and 28 give the limiting dimensions and tolerances for

major, pitch, and minor diameters of threads of special diameters,

pitches, and lengths of engagement.

2. Class 2, Free Fit.—This class is intended to cover the manufacture of threaded parts which are to assemble nearly or entirely

with the fingers, and where a slight amount of shake or play between

the assembled threaded members is not objectionable. It is the same

in every particular as class 1 except that it lias no allowance and the

tolerances are smaller.

i 2 Special threads having a length of engagement considerably less than one diameter will not develop

the full strength of the screw. The minimum minor diameter of the nut of the American National form of thread is such as to provide a minimum clearance on diameter at the minor diameter equal to two-ninths of the basic thread depth. If this clearance is reduced by providing a greater percentage of thread depth in the

nut, the strength of such a fastening is increased. In such cases when the screw is subject to considerable

tension, it is permissible to make the minor diameter of the nut less than the minimum specified in order to give the necessary depth of engagement. On the other hand, when the length of engagement is exceptionally long the minor diameter of the nut may be greater than the maximum specified without impairing the strength of the fastening. » See footnote 10, p. 80.
82 NATIONAL SCREW THREAD COMMISSION

Tables 27 and 29 give the limiting dimensions and tolerances for major, pitch, and minor diameters of threads of special diameters,

pitches, and lengths of engagement.

3. Class 3, Medium Fit.—This class is intended to cover the manu,

facture of the higher grade of threaded parts which are to assemble

nearly or entirely with the fingers, and must have the minimum amount

of shake or play between the threaded members. It is the same as

class 2 in every particular except that the tolerances are smaller. Tables 27 and 30 give the limiting dimensions and tolerances for major, pitch, and minor diameters of threads of special diameters,

pitches, and lengths of engagement.

4. Class 4, Close Fit.—This class is intended to cover the manufacture of threaded parts of the finest commercial quality, where

very little shake or play is desirable, and where a screw driver or wrench may be necessary for assembly.

In the manufacture of screw-thread products belonging to this class

it may be necessary to use precision tools, selected gages, and other

refinements. This quality of work should, therefore, be used only

in cases where requirements of the mechanism being produced are

exacting. In order to secure the fit desired, it may be necessary in some cases to select the parts when the product is being assembled.

The maximum pitch diameters of the screws are slightly larger

than the minimum pitch diameters of the nuts determined from

Table 27. Tables 27 and 31 give the limiting dimensions and tolerances for major, pitch, and minor diameters, of threads of special diameters,

pitches, and lengths of engagement.

4. TABLES OF DIMENSIONS

In order to simplify the specification of dimensions of special fastening screw threads, Tables 27, 28, 29, 30, and 31 are arranged herein, and

are intended to cover all practical combinations of diameter, pitch,

length of engagement, and class of fit. The use of these tables instead

of the application of formulas to determine limiting dimensions of a

special thread facilitates placing dimensions on drawings. Also, in cases of special threads of the same diameter, pitch, and class of fit, but slightly different lengths of engagement, the threads may be

gaged by a single set of gages, as identical pitch diameter tolerances

will be applied.

(a) Arrangement of Tables.—The arrangement of dimensions

and tolerances given in these tables has the following features:

All thread dimensions of threads of special diameters, pitches, and

lengths of engagement, except pitch diameter tolerances, are derived

from Table 27.
SPECIAL THREAD DIMENSIONS AND TOLERANCES 83

Pitch diameter tolerances are taken from Tables 28, 29, 30, and 31,

depending upon the class of fit required. These pitch diameter toler- ances were obtained by adding increments corresponding to the major

diameters at the top, the threads per inch at the side of the table, and mean lengths of engagement of %, 1, and 2}{ inches for pitches from

64 to 12 threads per inch, inclusive, and }{, 2, and 4K inches for pitches

> from 10 to 4 threads per inch, inclusive. Thus, the increments of

the pitch diameter tolerances based on length of engagement and on

diameter vary by definite steps instead of continuously. However,

in order that the tolerances given in these tables might be wholly

consistent with those given in Section III, certain values as listed are less than those yielded by the above method. This modification was made by inserting in the tables, in the positions corresponding to standard sizes, pitches, and lengths of engagement of the American

National coarse and fine thread series, the pitch diameter tolerances

listed in Section III. Then, wherever necessary, all values above

and to the left of these inserted values were reduced so that none of

them should exceed these standard values, and those below and to the right were increased so that none should be less than the standard

values. This has the important advantage that in a series of sizes,

frequently occurring in practice, consisting partly of standard sizes and partly of special sizes, there will be no undue irregularity in the

progression of the pitch diameter tolerance, with consequent diffi- culties in securing gages, etc. The maximum pitch diameter tolerances listed are equal to the

tolerances on the major diameter of the screws of the same pitch, as given in Table 27.

(b) Rules for Use of Tables.—For consistent application of

these pitch diameter tolerance tables to all cases, adherence to the

following rules relative to the use of the tables is necessary:

1. Tolerances on pitch diameter corresponding to major diameters

between those for which values are given in the tables shall be those

of the next larger diameter.

2. Tolerances on pitch diameter for pitches between those for

which values are given in the tables shall be those of the next coarser

pitch, except that for screws having 80, 72, 44, 13, 11, 9, 7, 5, or 4%

threads per inch, lengths of engagement of one and one-half diameters

or less, and diameters less than the standard diameters for the re- spective pitches as given in Section III, the tolerances given in Section

III shall be used.

3. Tolerances on pitch diameter for pitches coarser than 4 threads

per inch shall be the same as those for 4 threads per inch.

4. Tolerances on pitch diameter when the length of engagement is

}i, or \%, inches for 12 threads per inch and finer, or 1, or 3, inches
84 NATIONAL SCREW THREAD COMMISSION

for pitches coarser than 12 threads per inch, shall correspond to the

interval of which these are the upper limits.

5. Tolerances on pitch diameter for lengths of engagement greater

than those for which values are given shall be the maximum values

listed for the pitch concerned.

(c) Examples.—The following examples illustrate the use of these

tables

:

Example: 3%-inch, 16-thread, class 1, with allowance on screw, onehalf inch length of engagement:

From Table 28: Pitch diameter tolerance =0. 0095

Also from Table 27, for the screw: Maximum major diameter =3. 2500 —0. 0018 = 3. 2482

Minimum major diameter =3. 2482- . 0126=3. 2356

Maximum minor diameter=3. 2500— . 0785 =3. 1715 Maximum pitch diameter =3. 2500— . 0424 =3. 2076

Minimum pitch diameter =3. 2076— . 0095 =3. 1981 And for the nut: Minimum major diameter = 3. 2500 Minimum minor diameter =3. 2500— . 0677=3. 1823 Maximum minor diameter=3. 1823+ . 0068 = 3. 1891 Minimum pitch diameter =3.2500— .0406 = 3.2094

Maximum pitch diameter =3. 2094+ . 0095 = 3. 2189

Example: 3-inch, 24-thread, class 2, free fit, five-eighths inch lengt

of engagement:

From Table 29: Pitch diameter tolerance >=0. 0066

In this instance the pitch diameter tolerance is printed in italics. In accordance with the footnote under Table 29 it is desirable to avoid the use of tolerances set in italics as the combination of class of fit, length of engagement, pitch, and diameter is disproportionate.

If it is decided to use a closer fit, class 3-medium fit or class 4-close

fit may be chosen. Assuming the choice of class 3-medium fit, the

following dimensions are obtained:

From Table 30: Pitch diameter tolerance =0. 0065 From Table 27 for the screw: Maximum major diameter = 3. 0000

Minimum major diameter =3. 0000-0. 0066=2. 9934 Maximum minor diameter =3. 0000- . 0511=2. 9489 Maximum pitch diameter =3. 0000- . 0271 =2. 9729 Minimum pitch diameter =2. 9729- . 0065=2. 9664 And for the nut: Minimum major diameter = 3. J0G00 Minimum minor diameter =3. 0000— . 0451 =2. 9549

Maximum minor diameter=2. 9549+ . 0045=2. 9594

Minimum pitch diameter =3. 0000— . 0271 =2. 9729

Maximum pitch diameter =2. 9729+ . 0065=2. 9794
SPECIAL THKEAD DIMENSIONS AND TOLERANCES 85

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ill in in in in in

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§ SiI III III III III

HI in 111 in in in

eooc 11 S SiII III III III III

o c 1 in in in in ifII ill III III 111 111 III

III III ill III III III

111 ill III ill 111 i

; | III III ill ill ; III 111

|

i i I \ \ I ! ! i

CO T- CO

I

It

I

ii

11

ii

l

s1

18415°—29-
92 NATIONAL SCREW THREAD COMMISSION

i i III 111

' ' ° Hi

111 III III Ill

4

Hio '

• 111 III ill III III

111 III III ill 111 111 111

i\ i i ill

! ! ! Q • • III ill ill III III 1!

IS

IS ssl

f

m in III III 111 111 III III III

sill 111 Ill III ill III 111 111 III

1 sill III III III III III 111 III 111

sill III

Q •

• L_l_l HI hi hi in in hi

sin 8S ° SSS in in SSS 888 8! Ill Hi

4111 III III III III III III II! SSS sill Hi III HI III 111 III 111 111

sill 111 Hi hi in in Hi hi in

sill 111 111 11 111 111 ISSS

to \z> to mioto H i—( CO »—t •—< CO SSS SSS

sill ill 111 HI 111 ill HI 111 Hi

sill HI o • • 1—1

Hi hi in Hi Hi in in

sin -s SSS s II HI 111 111 II! 228 22! SSS SSS sill ill Hi hi hi hi in in in
sss

SPECIAL THREAD DIMENSIONS AND TOLERANCES

HI HI |il Hi in in in

111 111 III III III III ill III

HI in in hi in in in in

HI in in in in in in in

HI in in in in hi in in

ill HI III III HI HI III HI

II III III ill HI III III III

III III III III 111 III III III

III III III III III III III

III III ill III 111 III III III

II in in in in in in in

,a l III III III III III III III

HI in in in hi hi in in

111 III HI HI HI III HI HI

III 111 111 111 111 Hi III

HI in in in hi in

IT

111 111 111 III

111 ill

Is

li

ii

i

if

IS

8 .S II

! S3

I!
94 NATIONAL SCREW THREAD COMMISSION

If, instead, it is decided to reduce the length of engagement

one-half inch, the following dimensions are obtained:

From Table 29: Pitch diameter tolerance =0. 0060

From Table 27 for the screw: Maximum major diameter =3. 0000

Minimum major diameter =3. 0000 —0. 0066 =2. 9934 Maximum minor diameter =3. 0000— .0511 =2. 9489 Maximum pitch diameter =3. 0000— . 0271 =2. 9729

Minimum pitch diameter =2. 9729- . 0060=2. 9669

And for the nut: Minimum major diameter =3. 0000

Minimum minor diameter =3. 0000— . 0451 =2. 9549 Maximum minor diameter =2. 9549+ . 0045=2. 9594 Minimum pitch diameter =3. 0000— . 0271 =2. 9729 Maximum pitch diameter =2. 9729+ . 0060 = 2. 9789

5. SPECIFICATIONS FOR GAGES 14 (See also Section m, division 5, "Gages")

(a) Classification of Gages and Gage Tolerances.—Screwthread gages are classified according to accuracy into classes X, Y, an(

Z, the class X being the most accurate. The tolerance limits oi classes Y and Z "go" gages are placed inside of the extreme product

limits to provide allowance for wear of the gages. The tolerances on all "not go" gages, however, are applied from the extreme

product limit as the starting point, as no allowance for wear is necessary. Also, only one set of tolerances, namely, class X, is specified for "not go" gages. The selection of "go" gages from among these

classes for use in the inspection of threaded product depends entirely

upon the specifications for the product. For example, in the pro- duction of parts to class 4 specifications, class X gages may be required

for all purposes. On the other hand, for parts made to class 1 specifications, class Z gages may be sufficiently accurate for all purposes. The recommended uses for the various classes of gages are given in Table 32. In Tables 33, 34, and 35 are specified tolerances on

diameter, lead, and angle for each class of gage. "Go" gages may be permitted to wear' to the extreme product

limits. It is desirable, however, that working and inspection gages be

so selected that the dimensions of the working gages are inside of the

hmiting dimensions represented by the inspection gages, in order that

all parts passed by the working gage will be accepted by the inspection

gage. As to wear on "not go" gages, it is purely a question of econ- omy as to when the "not go" gage should be discarded. Continued

use reduces the available working tolerance on the product, and the

resulting loss must be balanced against the cost of a new gage.

11 In ordering gages for special threads the length of engagement of the component thread (as distinct from the length of the gage), as well as the diameter, pitch, and class of fit, should be stated.
GAGES FOR SPECIAL THREADS 95

(6) Thread Form of Plug and King Thread Gages.—The minor

diameter of the "go" thread ring gage is the same as the minimum

minor diameter of the nut or tapped hole with a minus gage tolerance.

The minor diameter of the "not go" ring gage is the minimum minor

diameter of the nut plus at least 0.0002 inch, with a plus gage tolerance.

Also the maximum major diameter of the "not go" thread plug gage

is at least 0.0002 inch less than the basic major diameter, with a minus

gage tolerance.

A relief is provided at the root of the "go" thread plug or ring

gage, the width of which is not greater than one-eighth of the pitch.

Also a relief is provided at the root of the "not go" plug or ring gage,

the width of which is approximately one-fourth of the pitch.

Thus contact of the "not go" thread gage on the sides of the

threads, rather than at the corners of the crest and root, is assured.

(c) Marking of Gages.—Each gage shall be plainly marked, for

identification, with the diameter, pitch, thread series—that is, "NS"

to indicate a special thread of American National form—and class of

fit. See Section II, division 2, " Symbols." For example, a 1-inch,

16-pitch gage of American National form of thread, class 3, medium

fit, shall be marked: 1"—16—NS—3. Table 32.

Recommended uses for classes X, Y, and Z gages

Class of fit Setting gage Inspection gage Working gage

2 3 4 Class 1 Class X Class Y Class Z. Class Y.

Do.

Class X.

do do

Class 3 do Class X

Class 4 do do Table 33.

Tolerances for class X "go" thread gages and all "not go" thread gages

Threads per inch Tolerance on pitch diameter 1 Tolerance

in lead 2 Tolerance on half angle of thread

Tolerance on major or minor diameters 1 From— To— From— To—

9 3 4 5 6 7 Inch Inch Inch Deg. Min. Inch Inch ± ±

64 0. 0000 0. 0002 0. 0002 30 0.0000 0. 0004

56 .0000 .0002 .0002 30 .0000 .0004

48 .0000 .0002 .0002 30 .0000 .0004

40 .0000 .0002 .0002 20 .0000 .0004

36 .0000 .0002 .0002 20 .0000 .0004

32 .0000 .0003 .0003 15 .0000 .0004

28 .0000 .0003 .0003 15 .0000 .0005

24 .0000 .0003 .0003 15 .0000 .0005

20 .0000 .0003 .0003 15 .0000 .0005

18 .0000 .0003 .0003 10 .0000 .0005

16 .0000 .0003 .0003 10 .0000 .0006

14 .0000 .0003 .0003 10 .0000 .0006

12 .0000 .0003 .0003 10 .0000 .0006

10 .0000 .0003 .0003 10 .0000 .0006

8 .0000 .0004 .0C04 5 .0000 .0007

6 .0000 .0004 .0004 5 .0000 .0008

4 .0000 .0004 .0004 5 .0000 .0009

1 On "go" plugs the tolerance is plus, and on "go" rings the tolerance is minus. On "not go" plugs the

tolerance is minus, and on "not go" rings the tolerance is plus.

1 Allowable variation in lead between any two threads not farther apart than the length of engagement.
96 NATIONAL SCREW THREAD COMMISSION

Table 34.Tolerances for class Y "go" thread gages

Threads per inch

Tolerance on pitch diameter 1 Tolerance

in lead 2 Tolerance on half angle of thread

Tolerance on major or minor diameters 1 From

To— From

To—

>

3 4 5 6 7

Inch Inch Inch Beg. Min. Inch Inch ± ±

64 0.0001 0.0004 0. 0002 45 0.0000 0. 0004

56 .0001 .0004 . 0002 45 .0000 .0004

48 . 0001 . 0004 . 0C02 45 .0000 . 0004

40 . 0001 .0004 . 0002 30 .0000 . 0004

36 . 0001 .0004 !0002 30 .0000 . 0004

32 . 0001 . 0C04 . 0003 20 0000 . 0004

28 !0002 !o005 . 0003 20 !oooo !0005

24 .0002 .0005 . 0003 20 .0000 .0005

20 .0002 .0005 .' 0003 20 .0000 .0005

18 .0002 .0005 .0003 15 .0000 .0005

16 .0002 .0006 .0003 15 .0000 .0006

14 .0002 .0006 .0003 15 .0000 .0006

12 .0002 .0006 .0003 10 .0000 .0006

10 .0002 .0006 .0003 10 .0000 .0006 8 .0002 .0007 .0004 5 .0000 .0007

6 .0003 .OOOS .0004 5 .0000 .0008

4 .0003 .0009 .0004 5 .0000 .0009

1 On "go" plugs the tolerance is plus, and on "go" rings the tolerance is minus.

2 Allowable variation in lead between any two threads not farther apart than the length of engagement. Table 35.

Tolerances for class Z "go" thread gages

Threads per inch

Tolerance on pitch diameter 1 Tolerance

in lead 1 Tolerance on half angle of thread

Tolerance on major or minor diameters i From

To— From— To—

2 3 4 5 6 7

Inch Inch Inch Beg. Min. Inch Inch ± h

64 0. 0002 0.0006 0. 0002 o" 45 0.0000 0.0004

56 .0002 .0007 .0002 45 .0000 .0004

48 .0002 .0007 .0002 45 .0000 .0004 40 .0002 .0007 .0002 30 .0000 .0004 36 . 0003 .0008 .0002 30 .0000 .0004

32 .0003 .0008 .0003 20 .0000 .0004

28 .0003 .0008 .0003 20 .0000 .0005 24 .0003 .0009 .0003 20 .0000 .0005

20 .0003 .0009 .0003 20 .0000 .0005

18 .0004 .0010 .0004 15 .0000 .0005

16 .0004 .0010 .0004 15 .0000 .0006 .0004 .0010 .0004 15 .0000 .0006

12 .0004 .0011 .0004 10 .0000 .0006

10 .0005 .0012 .0004 10 .0000 .0006

8 .0006 .0013 .0005 5 .0000 .0007

6 .0006 .0014 .0005 5 .0000 .0008

4 .0007 .0016 .0005 5 .0000 .0009

1 On "go" plugs the tolerance is plus, and on "go" rings the tolerance is minus.

2 Allowable variation in lead between any two threads not farther apart than the length of engagement.
AMERICAN NATIONAL HOSE COUPLING THREADS 97

SECTION V. AMERICAN NATIONAL HOSE-COUPLING AND

FIRE-HOSE COUPLING THREADS

Several years ago specifications for American National standard

fire-hose coupling threads were approved by the National Board of Fire Underwriters, National Fire Protection Association, American

Society of Mechanical Engineers, American Society of Municipal

Improvements, New England Water Works Association, American

Water Works Association, the Bureau of Standards, and other interested organizations. These specifications were published in 1911, as the Specifications of the National Board of Fire Underwriters, recom- mended by the National Fire Protection Association and approved

by the various other organizations. They were also published in

1914 as Circular No. 50 of the Bureau of Standards. This circular was revised and republished in 1917.

When the National Screw Thread Commission took up its work on

the standardization of screw threads, the specifications for fire-hose

coupling threads above referred to were accepted as the basis of

its work on fire-hose coupling threads. It was found, however, that

the specifications as originally drawn were inadequate in that they

specified nominal dimensions only, with no maximum and minimum

limits. From the best information available when fire-hose coupling threads were under discussion, the commission concluded that they should be

placed in the loose-fit class and that the allowance provided in the

original specifications should be interpreted as the minimum difference

in pitch diameter of the couplings and nipples; that is, that a looser

fit could be tolerated than that represented by the nominal dimensions^

but that a tighter fit would be objectionable. The nominal size of

the coupling was, therefore, taken as the minimum coupling, and the

nominal size of the nipple as the maximum nipple; the loose-fit tolerances being applied in such a direction as to make the maximum

coupling larger and the minimum nipple smaller than the nominal

size by the amount of the tolerance. The dimensions for American

National fire-hose coupling threads appearing in the 1921 Progress

Report of the commission were calculated on that basis. It later appeared from evidence presented by the National Board of

Fire Underwriters that the fits resulting from the limiting dimensions

specified in the 1921 Progress Report may in extreme cases be looser

than good practice warrants. The commission was, therefore, re- quested to revise its specifications for fire-hose coupling threads in

such a manner that the resulting fits would be somewhat closer than

those originally permitted. The revision requested was accomplished

by reducing the allowance between the minimum coupling and the

maximum nipple; the minimum coupling dimension being retained
98 NATIONAL SCREW THREAD COMMISSION

as published in the 1921 Progress Report. However, from evidence

presented by certain manufacturers, it appeared desirable to provide

a larger wear limit for gages and also permit the use of field inspection gages which were outside of the limits set for the manufacturers'

gages, in order to insure the approval, by the purchaser, of threaded

couplings which had passed the manufacturers' gages. To permit

this, the tolerances on both the coupling and nipple were increased

slightly.

Furthermore, since the publication of the 1921 Progress Report, it has been found desirable, in order to facilitate production and simplify

the manufacture of threading tools and gages, to adopt the American

National form of thread for American National fire-hose coupling

threads. This, however, is a very minor change and only slightly

affects the thread form at crest and root. The specifications have been further supplemented by recommended

limiting dimensions of gages such that every coupling and nipple

accepted by the gages will be known to be within the Hunting dimensions specified. Only such a system can insure that the finished

product will assemble and function properly.

Comparison of the resulting dimensions with those contained in the

original specifications of the National Board of Fire Underwriters and

in Bureau of Standards Circular No. 50, shows that the two are not in

conflict. The nominal dimensions originally specified for couplings

and nipples are not inconsistent with the above limiting dimensions,

and the revised dimensions should not be considered as changing in any way the original specifications for American National fire-hose

coupling threads, but as supplementing those specifications, and as expressing them in definite and measurable terms. It should be

understood that these dimensions for American National fire-hose

coupling threads are the limiting dimensions for the finished product

and not for the threading tools. With regard to the American National hose-coupling threads, which

range in size from three-fourths to 2 inches, the series of sizes and

pitches originally adopted by the commission are essentially the same

as the corresponding sizes of the American National straight pipe

threads, with the exception of the three-fourths-inch size. In this case 11 and 11 3^ threads, with a diameter of 1^ inches, were already

in very extensive use. The adoption of the so-called " straight iron

pipe thread'' was indorsed by the National Association of Brass

Manufacturers, and at the time of its adoption was recommended by

the committee on Small Hose Couplings of the National Fire Protection Association and tentatively adopted by that association.

In ordering threading tools for producing American National hosecoupling and fire-hose coupling threads, it should be pointed out that new taps should be near the maximum permissible size of the coupling,
AMERICAN NATIONAL HOSE COUPLING THREADS 99

and new dies near the minimum permissible size of the nipple, in order that reasonable wear may be provided. As the threading tools wear by use, the couplings will become smaller and the nipples larger

until the hmiting dimensions are reached. These must not be ex- ceeded. When the product reaches, or comes dangerously close to, the limiting size, the threading tools should be readjusted or replaced.

1. FORM OF THREAD

1. Angle of Thread.—The basic angle of thread (A) between the

sides of the thread measured in an axial plane is 60°. The line bisecting this 60° angle is perpendicular to the axis of the screw thread.

2. Flat at Crest and Root.—The flat at the root and crest of the basic thread form is Y% x Vi or 0.125 X p.

3. Depth of Thread.—The depth of the basic thread form is

7, nannnv 7, 0.649519

h = 0.649519 Xv, or h =

n . where

p = pitch in inches n = number of threads per inch

Ji = basic depth of thread

2. THREAD SERIES

(a) American National Hose-Coupling Threads.—There are

specified in Table 36 a thread series and basic dimensions for hosecoupling threads from % to 2 inches in diameter, which will be known

as the "American National hose-coupling threads."

The American National hose-coupling thread is recommended for use on all couplings and connections where sizes between % and 2

inches in diameter are required.

Table 36.American National hose-coupling threads BASIC MINIMUM COUPLING DIMENSIONS

Nominal size Number

of threads

per inch Pitch Depth of thread Major

diameter

Pitch diameter Minor

diameter Allowance

2 3 1 5 6 7 8 K 1 — - UH

iiH ny2 im

UH

Inch

0. 08696

. 08696

. 08896

. 08696

. 08696

Inch

0. 05648 .05648

. 05648 .05648

.05648

Inches

1. 0725

1. 3051

1. 6499

1. 8888

2. 3628

Inches

1. 0160

1. 2486

1. 5934

1. 8323

2. 3063

Inches

0. 9595

1. 1921

1. 5369

1. 7758

2. 2498

Inch

lm2 BASIC MAXIMUM NIPPLE DIMENSIONS

H l — 1Itf iy2 2 UH

0. 08696

. 08696

. 08696

. 08696

. 08696

0. 05648 .05648

.05648

.05648

. 05648

1. 0625

1. 2951

1. 6399

1. 8788

2. 3528

1. 0060

1. 2386

1. 5834

1. 8223

2. 2963

0. 9495

1. 1821

1. 5269

1. 7658

2. 2398

0.01

.0] * .01

.01 .01

1 The %-inch hose coupling is used on H-inch and %-inch, as well as on i^-inch, hose.
100 NATIONAL SCREW THREAD COMMISSION

(b) Ameeican National Fire-Hose Coupling Threads.—There

are specified in Table 37 a thread series and basic dimensions for fire- hose couplings from 2^ to 4 ^ inches in diameter which will be known

as the "American National fire-hose threads." These basic sizes and

dimensions correspond in all details to those recommended by the

National Fire Protection Association and by the Bureau of Standards.

The American National fire-hose coupling thread is recommended

for use on all couplings and hydrant connections for fire-protection

systems, and for all other purposes where hose couplings and connections are required in sizes between 2}4, and inches in diameter.

Table 37.American National fire-hose coupling threads BASIC MINIMUM COUPLING DIMENSIONS

Nominal size Number of threads per inch Pitch Depth of thread Major

diameter

Pitch diameter Minor

diameter Allowance

2 3 4 5 6 7 8

2.5000 7.5

6.0

6.0 4.0

Inch

0. 13333

. 16667

. 16667

. 25000

Inch

0. 08660

. 10825

. 10825

. 16238

Inches

3. 0836

3. 6389

4. 2639

5. 7859

Inches

2. 9970

3. 5306

4. 1556

5. 6235

Inches

2. 9104

3. 4223

4. 0473

5. 4611

Inch

3.0000

3.5000 4.5000 BASIC MAXIMUM NIPPLE DIMENSIONS

2.5000 7.5 0. 13333 0. 08660 3. 0686 2. 9820 2. 8954 0. 0150

3.0000.. 6.0 . 16667 . 10825 3. 6239 3. 5156 3. 4073 .0150

3.5000 6.0 . 16667 . 10825 4. 2439 4. 1356 4. 0273 .0200

4.5000 4.0 . 25000 . 16238 5. 7609 5. 5985 5. 4361 .0250

3. ALLOWANCES AND TOLERANCES

(a) Specified allowances and tolerances, given in Table 38, apply to American National hose-coupling and American National fire-hose

coupling threads. The tolerances represent extreme variations

permitted on the product. There are shown, in Figure 20, the rela- tions between nipple and coupling dimensions and thread form as

specified herein.

(b) The tolerance on the coupling is plus, and is applied from the

minimum coupling dimension to above the minimum coupling

dimension.

(c) The tolerance on the nipple is minus, and is applied from the

maximum nipple dimension to below the maximum nipple dimension.

(d) The pitch diameter tolerances provided for a mating nipple

and coupling are the same.

(e) Pitch diameter tolerances include lead and angle variations

(see footnote 1, Table 38).

(J) The tolerance on the major diameter of the nipple is twice

the tolerance on the pitch diameter.
AMERICAN NATIONAL HOSE COUPLING THREADS 101

(g) The tolerance on the minor diameter of the nipple is equal to the tolerance on pitch diameter plus two-ninths of the basic thread

depth. The minimum minor diameter of a nipple is such as to result in a flat equal to one-third of the basic flat (jiiXp) at the root when

the pitch diameter of the nipple is at its minimum value. The maximum minor diameter is basic, but may be such as results from the use of a worn or rounded threading tool.

!

Fig. 19.American National hose-coupling and American

National fire-hose coupling threads

See Tables 38, 39, and 40 for dimensions and tolerances.

(7i) The tolerance on major diameter of the coupling is equal to the tolerance on pitch diameter plus two-ninths of the basic thread

depth. The minimum major diameter of the coupling is such as to

result in a basic flat (YsXp) when the pitch diameter of the coupling

is at its minimum value. The maximum major diameter of the

coupling is that corresponding to a flat equal to one-third the basic

flat QiiXp).
102 NATIONAL SCREW THREAD COMMISSION

(i) The tolerance on the minor diameter of the coupling is twice

the tolerance on pitch diameter of the coupling. The minimum

COUPLING FORM

S/OTAT/Orst - FJtch

• 3* sic 7~hrea dDepth

0€4QS/9Jb 3 Depth of

/-f£A\sy L,jst£ Shows

Fig. 20.

American National hose-coupling and American National fire-hose coupling threads minor diameter of a coupling is such as to result in a basic flat (YsXp)

at the crest when the pitch diameter of the coupling is at its minimum

value.
AMERICAN NATIONAL HOSE COUPLING THREADS 103

Table 38.

Tolerances and allowances for American National hose coupling and

American National fire-hose coupling threads

Lead Errors in

errors half angle Threads l olerances consuming consuming Nominal size Allowances on pitch one-half of one-half of per inch diameter * pitch- pitch- diameter diameter

tolerances 2 tolerances

1 3 4 5 6

Inch Inch Inch Beg. Min. H 11% 0. 010 0. 0085 0. 0025 1 52

l im .010 .0085 .0025 1 52 m 11V2 .010 .0085 .0025 1 52 iy2 an .010 .0085 .0025 1 52

2 .010 .0085 .0025 1 52 2V2 m .015 .0160 .0046 2 17

3 6 .015 .0180 .0052 2 4

6 .020 .0180 .0052 2 4

4 .025 .0250 .0072 1 55

1 The tolerances specified for pitch diameter include all errors of pitch diameter, lead, and angle. The

full tolerance can not, therefore, be used on pitch diameter unless the lead and angle of the thread are perfect. Columns 5 and 6 give, for information, the errors in lead (per length of thread engaged) and in angle, each of which can be compensated for by half the tolerance on the pitch diameter given in column 4. If lead and

angle errors both exist to the amount tabulated, the pitch diameter of a nipple, for example, must be reduced by the full tolerance or it will not enter the "go" gage.

s Between any two threads not farther apart than the length of engagement.

4. TABLES OF DIMENSIONS

Table 39.

American National hose couplings, thread dimensions

COUPLING THREAD

Nominal

size Threads

per inch Pitch Depthof thread

Major diameter Pitch diameter Minor diameter

Maxi- mumToler- ance Mini- mumMaxi- mum

Toler- ance Mini- mumMaxi- mum

Toler- ance Mini- mum

1 i 3 4 5 6 7 8 9 10 11 13 13 H IIV2 ny2 ny%

11H

Inch

0. 08696

. 08696

. 08696

. 08696

. 08696

Inch

0. 05648

. 05648

Inches Inch Inches

1 1. 0725

1 1. 3051

1 1. 6499

11. 8888

Inches

1. 0245

1. 2571

1. 6019

1. 8408

2. 3148

Inch

0.0085

.0085 .0085

.0085

.0085

Inches

1. 0160

1. 2486

1. 5934

1. 8323

2. 3063

Inches

0. 9765

1. 2091

1. 5539

1. 7928

2. 2668

Inch

0. 0170

.0170 .0170

.0170 .0170

Inches

0. 9595

1. 1921

1. 5369

1. 7758

2. 2498

l1M- . 05648 1H .05648

2... .05648 12. 3628 NIPPLE THREAD

% llVi

11V2 IVA IW2

0. 08696 .08696

. 08696

.08696

. 08696

0. 05648 .05648

.05648

.05648

.05648

1. 0625

1. 2951

1. 6399

1. 8788

2. 3528

0. 0170

.0170 .0170

.0170

.0170

1. 0455

1. 2781

1. 6229

1. 8618

2. 3358

1. 0060

1. 2386

1. 5834

1. 8223

2. 2963

0.0085

.0085 .0085

.0085 .0085

0. 9975

1. 2301

1. 5749

1. 8138

2. 2878

2 0. 9495

1... 2 1. 1821 IK— 2 1. 5269

2 1. 7658

2 2. 2398 m2__

1 Dimensions for the minimum major diameter of the coupling correspond to the basic flat (

lAXp),

and the profile at the major diameter produced by a worn tool must not fall below the basic outline. The maximum major diameter of the coupling shall be that corresponding to a flat at the major diameter of the maximum coupling equal to ^Xp, and may be determined by adding l%Xh (or 0.7939p) to the maximum pitch diameter of the coupling.

2 Dimensions given for the maximum minor diameter of the nipple are figured to the intersection of the worn tool arc with a center line through crest and root. The minimum minor diameter of the nipple

shall be that corresponding to a flat at the minor diameter of the minimum nipple equal to AXp, and may be determined by subtracting the basic thread depth, h (or 0.6495p), from the minimum pitch diameter of the nipple.
104 NATIONAL SCREW THREAD COMMISSION

Table 40.American National fire-hose couplings, thread dimensions

COUPLING THREAD

Nominal

size Threads

per inch Pitch Depth

of thread

Major diameter Pitch diameter Minor diameter

Maxi- mumToler- ance Mini- mumMaxi- mum

Toler- ance Mini- mumMaxi- mum

Toler- ance Mini- mum

1 2 3 4 5 6 7 8 9 10 11 12 13

2y2 7.5

6

64

Inch

0. 13333

. 16667

. 16667

. 25000

Inch

0. 08660

. 10825+

. 10825+

. 16238

Inches Inch Inches

13. 0836

13. 6389

14. 2639

Inches

3. 0130

3. 5486

4. 1736

5. 6485

Inch

0. 0160 .0180

.0180

.0250

Inches

2. 9970

3. 5306

4. 1556

5. 6235

Inches

2.9424

3. 4583

4. 0833

5. 5111

Inch

0. 0320

.0360

.0360 .0500

Inches

2. 9104

3. 4223

4. 0473

5. 4611

33H

1 5. 7859 NIPPLE THREAD

2^ 7.5

6

64

0.13333

. 16667

. 16667

. 25000

0. 08660

. 10825+

. 10825+

. 16238

3. 0686

3. 6239

4. 2439

5. 7609

0. 0320 .0360

.0360 .0500

3. 0366

3. 5879

4. 2079

5. 7109

2. 9820

3. 5156

4. 1356

5. 5985

0. 0160

.0180

.0180

.0250

2. 9660

3. 4976

4. 1176

5. 5735

22. 8954

2 3. 4073

2 4. 0273 33H

2 5. 4361

1 Dimensions for the minimum major diameter of the coupling correspond to the basic flat Q/&X.P), and the profile at the major diameter produced by a worn tool must not fall below the basic outline. The maximum major diameter of the coupling shall be that corresponding to a flat at the major diameter of the maximum coupling equal to lUXp, and may be determined by adding l%Xh (or 0.7939p) to the maximum pitch diameter of the coupling.

2 Dimensions given for the maximum minor diameter of the nipple are figured to the intersection of the worn tool arc with a center line through crest and root. The minimum minor diameter of the nipple

shall be that corresponding to a flat at the minor diameter of the minimum nipple equal to HiXp, and may be determined by subtracting the basic thread depth, h (or 0.6495p), from the minimum pitch diameter of the nipple. 5. GAGES

(a) Gages for American National Fire-Hose Coupling

Threads.—It is recommended that American National fire-hose

coupling threads be inspected in the field by means of gages made

within the tolerances given in Table 41. Limiting dimensions for these gages are given in Tables 42 and 43.

It is further recommended that American National fire-hose coupling threads be given final inspection by the manufacturer by means

of gages made within the limiting dimensions given in Tables 42 and

43, by whatever amount may be desired, in order to avoid, as far as possible, disagreements which might otherwise arise as the result of slight differences in the sizes of gages. Table 41.

Tolerances on gages for American National fire-hose coupling threads

Allowable variation in lead between any two threads not

farther apart than length of engagement

Allowable

variation

in one-half angle of thread

Tolerance on diameter of minimum

thread gage

Tolerance on diameter of maximum

thread gage

2 3 I

Inch ±0.0005 -

Deg. Min. ±0 10 Inch

r +0.000

i +.001

Inch -0.000

-.001
AMERICAN NATIONAL PIPE THREADS 105

Table 42.Limiting dimensions of field inspection thread plug gages for couplings

{internal threads) 1

Nominal

size Threadsper inch

"Go" or minimum gage" "Not go" or maximum gage Major diameter Pitch diameter Major diameter Pitch diameter

Maxi- mumMini- mumMaxi- mum

Mini- mumMaxi- mum

Mini- mumMaxi- mum

Mini- mum

3 3 4 5 6 1 8 9 10

2.500

3.000. 3.500 4.500

7.5

6.0 6.0

4.0

Inches

3. 0846

3. 6399

4. 2649

5. 7869

Inches

3. 0836

3. 6389

4. 2639

5. 7859

Inches

2. 9980

3. 5316

4. 1566

5. 6245

Inches

2. 9970

3. 5306

4. 1556

5. 6235

Inches

3. 0836

3. 6389

4. 2639

5. 7859

Inches

3. 0826

3. 6379

4. 2629

5. 7849

Inches

3. 0130

3. 5486

4. 1736

5. 6485

Inches

3. 0120

3. 5476

4. 1726

5. 6475

i The minor diameters of plug gages and the major diameters of ring gages are undercut beyond the nominal diameters to give clearance for grinding or lapping. The allowable variation in lead between any

two threads not farther apart than the length of engagement is ±0.0005 inch. The allowable variation in

one-half angle of thread is ±10 minutes. Table 43.

Limiting dimensions of field inspection thread ring gages for coupling

nipples (external threads) 1

Nominal

size Threadsper inch

"Go" or maximum gage "Not go" or minimum gage

Pitch diameter Minor diameter Pitch diameter Minor diameter

Maxi- mumMini- mumMaxi- mumMini- mum

Maxi- mum

Mini- mum

Maxi- mum

Mini- mum

2 3 4 5 6 7 S 9 10

2.500 3.000

3.500 4.500

7.5

6.0 6.0 4.0

Inches

2. 9820

3. 5156

4. 1356

5. 5985

Inches

2. 9810

3. 5146

4. 1346

5. 5975

Inches

2. 9104

3. 4223

4. 0473

5. 4611

Inches

2. 9094

3. 4213

4. 0463

5. 4601

Inches

2. 9670

3. 4986

4. 1186

5. 5745

Inches

2. 9660

3. 4976

4. 1176

5. 5735

Inches

2.9114

3. 4233

4. 0483

5. 4621

Inches

2. 9104

3. 4223

4. 0473

5. 4611

1 The minor diameters of plug gages and the major diameters of ring gages are undercut beyond the nominal diameters to give clearance for grinding or lapping. The allowable variation in lead between any

two threads not farther apart than the length of engagement is ±0.0005 inch. The allowable variation in

one-half angle of thread is ±10 minutes. SECTION VI. AMERICAN NATIONAL PIPE THREADS

[Note.—See Preface] The material on the subject of pipe thread's presented herewith is essentially the same as that in the report prepared by a special committee of the Committee of Manufacturers on Standardization of

Fittings and Valves, acting in cooperation with pipe and gage manufacturers and the A. S. M. E. Committee on International Standards

for Pipe Threads. It was published in October, 1919, under the title "Manual on American Standard Pipe Threads." It has been in- dorsed by the American Society of Mechanical Engineers and the

American Gas Association, and is adopted by the commission with

only such changes as are necessary to bring it into conformity with

the remainder of the report. #
106 NATIONAL SCREW THREAD COMMISSION

The American National pipe-thread standard for taper threaded

pipe joints was formulated prior to the year 1882 by Robert Briggs,

of Philadelphia, Pa. This standard, with certain modifications and

additions, is now in general use throughout the United States and

Canada.

1. FORM OF THREAD

(a) Specifications.—1. Angle of thread.—The angle between the

sides of the thread is 60° when measured in an axial plane, and the

line bisecting this angle is perpendicular to the axis of the pipe for either taper or straight threads.

2. Depth of thread

}

b—The crest and root of the thread form are truncated an amount equal to 0.0330 p; the depth of thread is, therefore, equal to 0.8 2?. COUPUNG

Fig. 21.- American National taper pipe thread form

and notation

NOTATION

-4=60° angle of thread

a =30° one-half angle of thread y=l° 47' approx. taper angle =one-sixteenth inch per inch on diameter H=0.866025 p depth of 60° sharp V thread «

4=0.800000 p)depth of thread on work

1=0.923761 Hi

[•=0.033012 p] / =0.038120 H depth of truncation

1=0.041266 hi p=l/n pitch n=number of threads per inch 3. Taper of thread.—The taper of the thread is 1 in 16, or three- fourths inch per foot, measured on the diameter.

(b) Illustration.—There are shown in Figure 21 the relations as

specified herein for form of thread, and general notation. Special

notation is given in Figures 22, 23, and 25.

i £ While Mr. Briggs originally advocated a slightly rounded crest and root, cutting tools are actually

slightly flattened at the crest and root.

16 For a symmetrical straight screw thread, H=p cot a. For a symmetrical taper screw thread H=~

(cot2 a—tan^ y tan a), so that the exact value for an American National taper pipe thread is ff=0.865743 p

as against H=0.866025 p, the value given above. For an 8-pitch thread, which is the coarsest standard taper pipe thread pitch, the corresponding values of if are 0.108218 inch and 0.108253 inch, respectively, the differ- ence being 0.000035 inch. This difference being too small to be significant, the value of £2=0.866025 p continues ip use for threads of three-fourths inch, or less, taper per foot.
AMERICAN NATIONAL PIPE THREADS 107

2. SYMBOLS

The list of symbols given in Section II-2, together with additional

symbols given below, should be used in formulas for expressing rela- tions of pipe threads, on drawings, etc. Pitch diameter of thread at end of pipe E

Pitch diameter of thread at gaging notch _EX Pitch diameter of thread at L2 from end of pipe E% Maximum pitch diameter, external locknut thread Ee Minimum pitch diameter, internal locknut thread E{ Distance from gaging notch to end of pipe == normal engagement by hand Lx Length of effective thread L2 Outside diameter of pipe=major diameter of pipe thread at L2 from end of pipe_Z>

Internal diameter of pipe d

3. THREAD SERIES

(a) American National Taper Pipe Threads.—Taper external

and internal pipe threads are recommended for threaded pipe joints

and pipe fittings for any service. The sizes and basic dimensions of the " American National taper pipe threads" are specified in Table 44.

1. Outside diameter of pipe.—The outside diameters of pipe are given in column 5 of Table 44.

2. Diameters of taper threads.—The pitch diameters of the taper

threads are determined by formulas based on the outside diameter

of pipe and the pitch of thread. These are as follows 17 (see Symbols

above)

:

#0 = 1)- (0.05 D + l.l) p

E1 = E + 0.0625 £i

3. Length of thread.—The length of the taper external thread is determined by a formula based on the outside diameter of pipe and

the pitch of the thread. This is as follows 17 (see Symbols above)

:

Z2 =(0.8 D+ 6.8) p

4. Length of engagement.—The normal length of engagement between taper external and internal threads, when screwed together by

hand, is shown in column 6 of Table 44. This length is controlled

by means of gages.

5. Tolerances.—The tolerance on diameter is the equivalent of the

variation in diameter due to taper over one and one-half turns either

way from the basic dimensions.18

1 7 These formulas are not expressed in the same terms as the formulas originally established by Mr.

Briggs, because they are used to determine directly the pitch diameter and the length of effective thread,

•which includes two threads slightly imperfect at the crest; whereas the Briggs formulas determined the major diameter and the length of perfect thread, the two threads imperfect on the crest not being included

in the formula. However, both forms give identical results.

is On account of the gage tolerance of one-half turn on working gages, this is equivalent to one turn plus

or one turn minus from the gaging notch when using working gages. (See figs. 29 and 30.) 18415°—29 8
NATIONAL SCREW THREAD COMMISSION

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AMERICAN NATIONAL PIPE THREADS

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110 NATIONAL SCREW THREAD COMMISSION

(Z>) American National Straight Pipe Threads.—The specified sizes and basic dimensions on the "American National straight

pipe threads" are given in Table 45.

1. Diameters oj straight threads.—The basic pitch diameter of the straight thread is equal to the diameter at the gaging notch of American National taper pipe thread, and is determined by the

following formula based on the outside diameter of pipe and the

pitch of thread (see Symbols above)

:

£i=2?-(0.05 2?+ 1.1)^ + 0.0625 U

Fig. 22.

American National taper pipe thread notation

NOTATION

-Eo=Z>-(0.05-D+l.l) P

.Ei =#o+0.0625 Li Li=p (0.8D+6.8) h=0.8p

2. Tolerances.—The tolerance on pitch diameter of a straight

pipe thread is the equivalent of the variation in diameter over one and

one-half turns either way from the gaging notch of the American

National taper pipe thread. 19 (See columns 4 and 6 of Table 45.)

3. Application to internal threads.—Straight threaded internal

wrought iron or wrought steel couplings of the weight known as "standard" may be used with taper threaded pipe for ordinary

19 The coupling thread may be gaged with a taper threaded plug gage. On account of the gage toler- ance of one-half turn on working taper pipe thread gages, the working tolerance is equivalent to one turn

either way from the gaging notch. In gaging, care must be taken to gage at the first thread and not at the end of the coupling when the thread is chamfered.
AMERICAN NATIONAL PIPE THREADS 111

pressures, as they are sufficiently ductile to adjust themselves to the

taper external thread when properly screwed together.

For high pressures, only taper external and internal threads should

be used.

4- Application to external threads.—Straight external threads are recognized only for special applications, such as long screws and

tank nipples.

r

Et ~ Boskfnkh diem.

J>}tck dam.afoaftHf

u fiOfch 0/fajbzrSee table 45 for relation to

taper thread

Fig. 23.American National straight pipe thread

notation (internal) Note.—This thread is gaged with the taper threaded plug gage and

should gage flush at the face with the gaging notch, allowing a maximum

variation of one turn plus or minus from the notch. Table 45.

Dimensions of American National straight pipe threads {for couplings

[For notation see fig. 23]

Nominal sizes in inches Threads

per inch Major

diameter, 1 basic

Pitch diameter Minor

diameter 1 Maximum Basic Minimum Basic

1 S 3 4 5 6 7

Inches Inches Inches Inches Inches

y% - 27 0. 40439 0. 37823 0. 37476 0. 37129 0. 34513 XX—

18 . 53433 . 49510 .48989 .48468 . 44544

18 . 67145 . 63222 . 62701 . 62181 . 58257 X 14 . 83557 . 78513 . 77843 . 77173 . 72129 x — 14 1. 04600 . 99557 . 98887 . 98217 . 93172

1 im 1. 30819 1. 24678 1. 23863 1. 23048 1. 16907 IX nx 1. 65294 1. 59153 1. 58338 1. 57523 1. 51382 IX xm 1. 89190 1. 83049 1. 82234 1. 81418 1. 75277

2 ny2 8

2. 36583 2. 30442 2. 29627 2. 28812 2. 22671 2y2 2. 86216 2. 77388 2. 76216 2. 75044 2. 66216

3.... 8 3. 48850 3. 40022 3. 38850 3. 37678 3. 28850 3H 8 3. 98881 3. 90053 3. 88881 3. 87709 3. 78881

4 8 4. 48713 4. 39884 4. 38712 4. 37541 4. 28713 *X 8 4. 98594 4. 89766 4. 88594 4. 87422 4. 78594

6 8 5. 54929 5. 46101 5. 44929 5. 43757 5. 34929

6 8 6. 60597 6. 51769 6. 50597 6. 49425 6. 40597

1 The American National pipe thread form is maintained; therefore, the major and minor diameters vary

with the pitch diameter and are determined by the threading tools.
112 NATIONAL SCREW THREAD COMMISSION

5. Application to long screw joints.—Long screw joints are used

to a limited extent. This joint is not considered satisfactory when

subjected to high temperature or pressure. In this application the

coupling has a straight thread and must make a joint with an American

National taper pipe thread. (See fig. 23.) It is necessary that the AMERICAN NATIONAL STRAIGHT PIPE THREAD AMERICAN NATIONAL TAPER

PIPE THREAD

Fig. 24.

Illustration of "long screw" joint between straight threaded coupling

and taper threaded pipe

coupling be screwed on the straight external thread for the full length of the coupling and then back until it engages the taper external

thread. The straight thread on the pipe enters the coupling freely

by hand, the joint being made by a packing material between the

locknut and the coupling. (See fig. 24.)

On account of the long engagement of thread, imperfections in pitch affect the fit when the coupling is screwed on the pipe its full length. Refinements of manufacture and gaging to insure a properly interchangeable product are more costly than the commercial

use warrants; therefore, the use of this type of joint is not recom- mended. For this reason, specifications for tolerances and gaging

are not included herein.

£i

Minimumpitch ot*»i*t. fltAtmm P/TCHOJfint. Fig. 25.

American National locknut thread notation

NOTATION

Ei =pitch "diameter at gaging notch of American National taper plug gage

JBe =-Ei+(4pX0.0625)

.Ei=.Ei+(5pX0.0625) Note.—See Table 46 for relation to taper pipe thread.
AMERICAN NATIONAL PIPE THREADS 113

(c) American National Locknut Threads.—Occasional re- quirements make it advisable to have a straight thread of the largest

diameter it is possible to cut on a pipe. This practice has been

standardized and is known as "maximum external and minimum

internal locknut threads." For dimensions, see Table 46. The

"tank nipple" shown in Figure 26 is an example of this thread. In

this application an American National standard taper pipe thread is

v cut on the end of the pipe after having first cut the "external locknut

thread."

Fig. 26.Illustration of "tank nipple" thread Table 46.

Dimensions of American National locknut threads

[For notation, see fig. 25]

Nominal size in inches Threads

per inch Ee

(Maxi- mum) i Ei

(Mini- mum) 1 Depth of thread

1 2 3 4 5

y% - - —

27 Inches

0. 38402 Inches0. 38633 Inch0. 02963 H 18 . 50378 . 50725 . 04444 % 18 . 64090 . 64437 . 04444

Yi 14 . 79629 . 80075 . 05714 % 14 1. 00672 1. 01119 . 05714

1 im

ny2 1m

uy2 8

1. 26037 1. 26580 . 06957 1H 1.60512 1. 61055 . 06957 \y2

1. 84408 1. 84951 . 06957

2 2. 31801 2. 32345 . 06957 2H 2. 79341 2. 80122 . 10000

3 8 3. 41975 3. 42756 . 10000 8 3. 92006 3. 92787 . 10000

4 8 4. 41838 4. 42619 . 10000 4V2 8 4. 91719 4. 92500 . 10000

6 8 5. 48054 5. 48836 . 10000 6 8 6. 53722 6. 54503 . 10000

7 8 7. 53359 7. 54141 . 10000

8 8 8. 53128 8. 53909 . 10000 9

00

00 9. 52922 9. 53703 . 10000

10. 10. 65219 10. 66000 . 10000

11. 8 11. 65063 11. 65844 . 10000

12 8 12. 64906 12. 65688 . 10000

1 A tolerance equivalent to one and one-half turns of the American National taper pipe thread is recom- mended, the tolerance being minus on Ee and plus on Ei.
114 NATIONAL SCREW THREAD COMMISSION

4. TABLES OF PIPE DIMENSIONS

Tables 47, 48, 49, and 50, which follow, are not a part of the

thread standard, but are reprinted as part of the Manual on Ameri- can Standard Pipe Threads.

Table 47.Dimensions of standard wrought pipe

Nominal sizes in inches Inside diameter

Outside

diameter Nominal

thickness

Transverse areas

Internal Metal

Length

of pipe

per square

foot of external

surface

y2 .- X—

m.

2... 2M3... 3H4___

5... 6—

_

7 i__ 8i._ 8—i

9i._

10i.

10 i. 10-.

11 i- 12 1. 12-.

Inches

0. 269 .364

.493

.622

.824 1.049

1. 380

1. 610

2. 067

2. 469 3.068

3. 548

4. 026

4. 506

5. 047

6.065

7. 023

8. 071

7. 981

8. 941

10. 192

10. 136

10. 020

11. 000

12. 090

12. 000

Inches

0. 405

.540

.675 .840

1. 050

1.315

1.660 1.900

2. 375

2. 875

3.500

4. 000 4.500

5.000

5. 563

6. 625

7. 625

8. 625

8. 625

9. 625

10. 750

10. 750

10. 750

11. 750

12. 750

12. 750

Inch

0. 068

.088

.091

.109

.113

.133 .140

.145

.154

.203

237

25S

.301

.277 .322

.342

.279 .307

.365

.375

.330

.375

Square

inches

0. 057 .104

.191

.304 .533 .864

1. 495

2. 036

3. 355

4. 788

7. 393

9. 886

12. 730

15. 947

20. 006

28.891

38. 738

51. 161

50. 027

62. 786

81. 585

80. 691

78. 855

95. 033

114. 800

113. 097

Square

inches

0. 072

.125 .167

.250

494

1. 075

1. 704

2. 228 2.680

3. 174 3.688

4.300

5. 581

6. 926

7.265

8. 399

9. 974

9. 178

10. 072

11.908

13. 401

12. 876

14. 579

Feet

9. 431 7.073

5. 658

4. 547

3. 637 2.904

2. 301

2. 010

1.608

1. 328

1. 091 .954

.848

.763

576

500 442

442

396

355

355

355

325

299

i Not included in simplified list of sizes as given in Department of Commerce Simplified Practice Recommendation No. 57.
PIPE DIMENSIONS

Table 48.

Dimensions of extra strong wrought pipe

115

Nominal siz 3s in inches Inside diameter Outside

diameter Nominal

thick- ness

Transve

Internal

rse areas

Metal

Length of pipe per square

foot of external

surface

Nominal

TirpiorVi-f- pel iUUt, plain enas

1 3 4 5 6 7 8

Inches Inches

£>QUQTe

lTlCIl In h inches inches Jrounds

0. 215 0. 405 0. 095 0. 036 0.093 9.431 0.314

.302 .540 .119 .072 .157 7. 073 .535 n— —

. 423 . 675 . 126 . 141 . 217 5. 658 . /OS I

'. 546 . 840 '. 147 . 234 ' 320 A KAt 1. UO(

'. 742 L 050 154 . 433 . too O. 001 1X. 4/0

1 - .957 1. 315 .179 .719 .639 2. 904 2. 171 1M 1. 278 1. 660 . 191 1. 283 881 L. OUi O QQfi ^. yyo m 1. 500 l! 900 . 200 1 767 1. UOO 2. 010 3. 631

2 L 939 2. 375 . 218 2 953 1 477 i fins 1. DUO O. VJ&Z

2. 323 2! 875 ".276 4 238 2. 254 1. 328 7.661 3__ 2. 900 3. 500 . 300 6. 605 3. 016 1 091 10 252 va 3. 364 4. 000 '. 318 8 888 3 678 . »D4 1^. DUD 4_. 3. 826 4 500 . 337 11 497 4 407 QAQ 1/1 QQQ 14. yoo 4M 1 —- A. 290 5. 000 !355 14! 455 5! 180 .763 17. 611

5. 4. 813 5. 563 .375 18. 194 6.112 .686 20. 787

6 5. 761 6. 625 .432 26. 067 8. 405 .576 28. 573 7» 6. 625 7. 625 .500 34. 472 11. 192 .500 38.048 8._ 7. 625 8. 625 .500 45. 663 12. 763 .442 43. 388 9__ 8.625 9.625 .500 58. 426 14. 334 .396 48. 728 10_ 9. 750 10. 750 .500 74. 662 16. 101 .355 54. 735 111 10. 750 11. 750 .500 90. 763 17. 671 .325 60. 075

12 11. 750 12. 750 .500 108. 434 19. 242 .299 65. 415

1 Not included in simplified list of sizes as given in Department of Commerce Simplified Practice Recommendation No. 57. Table 49.

Dimensions of double extra strong wrought pipe

Nominal sizes in inches Inside diameter Outside

diameter Nominal

thick- ness

Transverse areas

Internal Metal

Length of pipe per square

foot of external

surface

4M 1 66... 7i„

Inches

0. 252 .434

1. 100

1. 503

1. 771

2. 300 2.728

3. 152

3. 580

4. 063

4. 897

5. 875

6.875

Inches

0.840

1. 050 L 315

1.660 t 900

2. 375

2. 875 3.500

4.000

4. 500 5.000

5. 563

6. 625 7.625

8.625

Inch

0.294 .308

.358

.382 .400

.436

.552 .600

.636

.674 .710

.750

.864

.875

.875

inches

0. 050 .148

.282 .630 .950

1.774

2. 464

4.155

5.845

7. 803

10.066

12. 966

18. 835

27. 109

37. 122

Square

inches

0. 504 .718

1. 076

1. 534

1. 885 2.656

4. 028

5. 466

6. 721

8. 101 9.569

11. 340

15. 637

18. 555

21. 304

Feet 4.547

3. 637

2. 904

2. 301

2. 010

1. 608

1. 328

1.091 .954 .848

.763

.686

.576 .500

.442

1 Not included in simplified list of sizes as given in Department of Commerce Simplified Practice Recommendation No. 57.
116 NATIONAL SCREW THREAD COMMISSION

Table 50.Diameters of large 0. D. pipe

Nominal sizes in inches

Outside diameter

Inside diameter

\i inch

thick

Yie inch

thick

z/i inch

thick

7A& inch

thick inchthick ^6 inch

thick

5A inch

thick % inch

thick

1 inch

thick

1 3 3 i 5 6 7 8 9 10 11

14

1516

1 71820

Inches

14

1516

17

182022

24

26

28

30

Inches 13% i4l

15% 16%

17%

Inches 13% uys WA

Yl% 19%

21%

Inches 13%

14%

15%

1634 17%

19%

21M

23J4 25%

Inches 13%

14% 15%

16%

17%

19% 21% 23%

25%

27% 29%

Inches

1314

1516

17

1921

2325

2729

Inches 12%

13% 14%

15% 16%

18%

20%

22%

24%

26% 28%

Inches 12% im

14% 15%

16M 18%

20%

22%

24|| 26%

28%

Inches 12%

13%

14%

15% 16%

18% 20%

22%

24%

26%

28%

Inches

12

13

14

1516

18 22

2426

28

30

GAGE

/poors </A/o&i€tnr

Fig. 27.

Master gages or check gages for checking working gages

5. GAGES

In order properly to maintain interchangeability of pipe threads

gages should consist of " master," " check" or " setting, " ^inspection," and " working" gages. The same fundamentals apply as those

outlined in Section III covering gages for fastening screws, with

the single exception that, with taper threaded gages, separate "go"

and "not go" gages are not necessary.

(a) Classification of Gages.—1. Master gage.—The master gage

is a taper threaded plug gage. The roots of the threads are cut

to a sharp V or may be undercut to facilitate the making of the

thread. The crests are truncated an amount equal to 0.1 p. (See
GAGES FOU PIPE THREADS 117

fig. 27.

)

20 Basic dimensions of taper pipe thread gages are given in

Table 55. This gage is provided with the gaging notch as illustrated

in Figure 27. The master gage is the gage to which all other gages

are ultimately referred, either by transfer of measurements or direct

comparison by engagement. It is intended primarily for the use of gage and thread tool manufacturers.

2. Check {or reference) gages.—The check gages consist of a plug

gage, similar in all respects to the master gage, and one ring gage.

The ring gage has a thickness equal to dimension Lu is the same

diameter at the small end as the small end of the plug gage, and is flush with the plug gage at the small end and at the gaging notch

when screwed on tight by hand. (See fig. 27.) The check plug gage

is used to inspect inspection and working taper threaded ring gages.

Cf?£STS

PITCH DIAMETER^

7~JlF>£ft /f/vJGM£ASl//?£D OA/ QM/>t&T&R

Fig. 28.Inspection or working gages for checking product

The check ring gage is used to compare the check plug with the

master plug, or the inspection and working plug gages with the

check plug gage.

3. Inspection gages.—Inspection gages consist of one taper

threaded plug gage and one taper threaded ring gage. The roots of

the threads are cut to sharp V or may be undercut to facilitate making

the thread. The crests are truncated an amount equal to 0.1 p, but otherwise the gages are made to the dimensions given in Table

44.20 The ring gage has a thickness equal to dimension Lu and the same diameter at the small end as the small end of the plug gage.

(See fig. 28.)

J0 The object of truncating the crests on gages (truncation 0.1 p) is to insure that, when gaging commercial threads cut with a slightly dull tool, the gage bears on the sides of the thread instead of on the

roots.
118 NATIONAL SCREW THREAD COMMISSION

Inspection gages are for the use of the purchaser of pipe thread

products. When used, the extreme tolerances on the work should

be applied. This tolerance is one and one-half turns either way

from the gaging notch in the case of internal threads inspected with

the inspection plug gage, and when inspecting external threads the

tolerance is one and one-half turns either way from the small end

of the inspection ring. Inspection gages should be checked fre- quently against the check gages, and in use their errors should be

taken into account.

4- Working gages.—The working gages consist of one taper

threaded plug and one taper threaded ring gage. These gages are similar in all respects to the inspection plug and ring gages. The

working gages are used by the manufacturer to inspect his product.

In using the working gages, the tolerance to be applied is one turn AMERICAN NATIONAL TAPER

/HTE&NftL THREAD INTERNAL TH*£AI> /NTE-RN4L. THf?£AD

BASIC S/Z£. MAXltWMS/Z£ MiNiMUm SIZE

Fig. 29.Gaging of internal American National taper pipe threads either way from the gaging notch in the case of internal threads

inspected with the plug gage, and in the case of external threads the

tolerance is one turn either way from the small end of the working

ring gage.

(b) Gaging Practices.—1. Gaging internal threads.—The in- spection and working plug gages, Figure 29, should screw tight byhand into the fitting or coupling until the notch is flush with the face. When the thread is chamfered, the notch should be flush with the

bottom of the chamfer. The fitting or coupling is within the working

or net tolerance if the working gage notch is within one turn of the

coupling or fitting face when screwed in tight by hand. In the same way the coupling or fitting is within the inspection or extreme toler- ance if the inspection gage notch is within one and one-half turns of the coupling or fitting when screwed on tight by hand.

This method of gaging is used either for taper internal threads or

for straight internally threaded couplings which screw together with

taper external threads.
GAGES FOR PIPE THREADS 119

2. Gaging taper external threads.—The ring gage, Figure 30, should screw tight by hand on the pipe or external thread until the small

end of the gage is flush with the end of the thread. The pipe or

external thread is within the working or net tolerance if the working

ring gage screws on until the end of pipe or external thread is within one turn of the small end of the gage. The pipe or external thread

is within the inspection or extreme tolerance if the inspection ring

% screws on until the end of pipe is within one and one-half turns of

the small end of the gage.

(c) Specifications for Gages.—1. Master gages.—Master gages

shall be made within the closest possible limits of error. In no

case shall the accumulative error exceed the total accumulative

tolerance on diameter given in Table 51. Each master gage shall be accompanied by a report showing the error on each of the ele- ments of thread and a statement of the accumulative error derived

from the errors in the various elements. In case of question, the

BXTERKAL THREAD EXTERNAL THREAD EXTERNAL THREAD

BASIC SIZE MAUfHUM SITLE />7//V/fl?US*7 SfZE,

Fig. 30.Gaging of external American National taper pipe threads deviations of this gage from the basic size shall be ascertained by

the Bureau of Standards at Washington, D. C.

2. Check {or reference) gages.—Column 2 of Table 51 gives the

maximum allowable accumulation of all errors in the thread surface

of a check gage, expressed in terms of diameter, as illustrated in

Figure 31. No point on the thread surface of the gage should be

outside the zone of tolerance indicated by the shaded portion of the

illustration. This column is used when checking gages by measurement. If the errors in the gage are reported in terms of pitch,

angle of thread, and diameter, Tables 53 and 54 may be used to determine the accumulation of these errors for comparison with

column 2. In Table 53 the results of errors in angle are expressed

in terms of diameter. In Table 54 the results of errors in pitch are expressed in terms of diameter.

For example: A three-fourths inch, 14 thread, pipe thread plug

gage is reported as follows

:

Pitch diameter, large end, 0.98881 inch. Pitch diameter, small end, 0.96775 inch. One-half included angle of thread, 29° 58'. Maximum error in lead, 0.00007 inch.
120 NATIONAL SCREW THREAD COMMISSION

The correct pitch diameter at large end is 0.98886 inch. The error

is 0.00005 inch. The correct pitch diameter at small end is 0.96768

inch. (See Table 44.)

Error of 2' in angle is equivalent to 0.00005 inch; 0.00007 inch

error in lead is equivalent to 0.00012 inch. (See Table 44.) The

accumulative error at large end in terms of diameter = 0.00023 inch.

The accumulative error at small end equals 0.00025 inch.

The gage falls within the limits of the check gage (0.00028 inch as given in Table 51).

TAPER 1 ImIGmEASVQED ON DJAfll.

AXIS

C £ &

Fig. 31.Relation of tolerance to basic dimensions of a

correct taper pipe thread gage

•Eo=basic pitch diameter at small end of gage B=minimum pitch diameter at small end of gage C=maximum pitch diameter at small end of gage B=E —column 2 from Table 51 for check gages, or column 2 from Table

52 for new working gages C=jS +column 2 from Table 51 for check gages, or column 2 from Table

52 for new working gages Note.—No point of the thread surface of the gage should be outside

of the zone of tolerance indicated by the shaded portion of the illus- tration. The dotted line indicates the outline of a correct gage made

exactly to the basic dimensions. Column 3 of Table 51 gives the equivalent of column 2, expressed

in terms of distance parallel to the axis, and represents the maximum distance which a check ring gage of correct thickness, or a check plug gage of correct length from small end to gaging notch,

may vary from being flush at the gaging notch, or at the small end,

when referred to basic dimensions. It is equal to sixteen times

column 2 because of the basic taper of 1 in 16, measured on the diameter. This column is used when checking check gages by comparison

with a master gage. The necessary allowance must be made for the

error in the master gage. Column 4 of Table 51 gives the equivalent of column 3, expressed

in terms of the decimal part of a turn. This column is also used

when checking check gages by comparison with a master gage. The

necessary allowance must be made for the error in the master gage.
GAGES FOE, PIPE THREADS 121

A tolerance of plus or minus 0.0002 inch is allowed on the distance

between the gaging notch and the small end of the check plug gage,

or on the thickness of the check ring gage.

It is possible for check plug and ring gages, which come within all of the above tolerances, to vary from being flush with each other at the small end, or at the gaging notch, when screwed together tight

by hand. The maximum variation which might occur, expressed in

terms of distance . is given in column 5 of Table 51.

3. Inspection gages.—The tolerances on new inspection gages are the same as on working gages. (See Table 52.)

4- New working gages.—Column 2 of Table 52,gives the maximum

allowable accumulation of all errors in the thread surface of new

working gages, expressed in terms of diameter, as illustrated in

Figure 31. No point in the thread surface of the gage should be

outside of the zone of tolerance indicated by the shaded portion of the

illustration. This column is used when checking gages by measurement.

Column 3 of Table 52 gives the equivalent of column 2, expressed

in terms of distance parallel to the axis, and represents the maximum

distance which a new working ring gage of correct thickness, or a new working plug gage of correct length from small end to gaging

notch, may vary from being flush at the gaging notch, or at the small

end, when referred to basic dimensions. It is equal to sixteen times

column 2, because of the basic taper of 1 in 16, measured on the

diameter. This column is used when checking working gages by

comparison with a gage the error of which is known. The necessary

allowance must be made for this error. Column 4 of Table 52 gives the equivalent of column 3, expressed

in terms of the decimal part of a turn. This column is also used

when checking working gages by comparison with a gage the error

of which is known. The necessary allowance must be made for this

error. A tolerance of plus or minus 0.0005 inch is allowed on the distance

between the gaging notch and the small end of the working plug

gage, or on the thickness of the working ring gage.

It is possible for working plug and ring gages which come within

all of the above tolerances to vary from being flush with each other

at the small end or at the gaging notch, when screwed together tight

by hand. The maximum variation which might occur, expressed in

terms of distance, is given in column 5 of Table 52. It is also possible for working plug and ring gages which come

within all of the above tolerances to vary from being flush at the

small end or at the gaging notch, when screwed tight by hand on a

reference gage which comes within the tolerances specified for refer-
122 NATIONAL SCREW THREAD COMMISSION

ence gages. The maximum variation which might occur, expressed

in terms of distance, is given in column 6 of Table 52.

5. Worn working gages.—The maximum wear on working gages

must not be more than the equivalent of one-half turn from the basic

dimensions.

In order that no work passed by the working gage shall be rejected

by the inspection gage, it will be necessary to discontinue the use of the working gage when it has worn one-half turn; that is, the working

gage should always be kept within the tolerance equivalent of one

turn from the basic dimensions.

Table 51.

Tolerances for check (or reference) gages, American

pipe threads National taper

Nominal sizes in inches

Total ac- cumulative

tolerance on diameter (see

fig. 31)

Equivalent

longitudi- nal varia- tion (16X column 2)

Equivalent

angular

variation expressed

as decimal

part of one

turn

H3 8- V2- Hi-_ MIVi

2... 2J4

3__. 4_.

5_. 6-

7„.

8...

9__. 10- . 11- . 12_.

14_.

15-.

16..

17.. 18.. 20.. 22..

24..

26..

28_. 30_.

Inch

0. 00020

.00022

.00024 .00026 .00028

. 00030

.00032

.00034

. 00036

.00038

. 00038

.00041 .00043 .00045

.00047

.00051 .00055

.00059

.00063 .00066 .00070

. 00074

.00082

.00090

. 00094

. 00106

. 00113

. 00121

. 00129

, 00137

00144

Inch

0. 0032

.0035

.0038

.0042 .0045

.0048

.0051 .0054

.0058

.0061

.0061 .0066

.0069

.0072 .0075

.0082

.0088

.0094

.0101 .0106 .0112

.0118

.0131 .0138 .0144

.0150

.0157

.0170

.0181 .0194

.0206

.0219 .0230

.059

.063

.055

.059 .062

.067 .050 .050

.053 .055

.058

.065 ,070

.075

,0S0 085

,095

,105 ,110

115 120

125 135

145

155

165

175 185

1 Maximum amount it is possible for plug and ring gages to vary from being flush at small end or at gaging notch when screwed together tight by hand (2 times column 3+0.0004 inch).
GAGES FOR PIPE THREADS 123

Table 52.

Tolerances for inspection and working gages, American National taper pipe threads

Nominal sizes in inches

Vs- %

ki_- 1%

ltt 2_- 2V2 3—

m4_. 5_.

6.- 7_- 8_.

9__

10. 11. 12.

14_

15. 16-

17-

18.. 20.

22.

.

24 _ 26_

28.

30 _

Total ac- cumulative"

tolerance on diameter

(see fig. 31)

Inch

0. 00040

.00044

. 00048

. 00052

. 00056

. 00060 .00064

. 00068

. 00072

. 00076 .00076

. 00082

. 00086 .00090

. 00094

. 00102

. 00110

. 00118

. 00126

. 00132

. 00140

. 00148

.00164

. 00172

. 00180 .00188

. 00196

. 00212

. 00226

. 00242

. 00258

. 00274

Equivalent longi- tudinal

variation

(16 X

column 2)

Inch

0. 0064 .0070

.0077

.0083

.0102

.0109

.0115

.0122

.0122

.0131

.0138 .0144

.0150

.0163

.0176

.0189

.0202

.0211 .0224

.0237

.0262 .0275

.0301 .0314

.0339

.0387

.0413 .0438

.0461

(<)

0. 172 .126

.136

.118

.126

.110

.118

.124 .134

.100 .100

.105 .110

.115

.120

.130 .140

.150

.160 .170

.180

.190

.210

.220 .230 .240

.250

.270 .290

.310

.330

.350 .370

(»)

Inch

0. 0138

.0150

.0164

.0176 .0190

.0202

.0214 .0228

.0240

.0254

.0254

.0272

.0286

.0298 .0310

.0336

.0362

.0388 .0414

.0432

.0458

.0484 .0534

.0560 .0586

.0611 .0638 .0688

.0734

.0784

.0932

(

3 )

Inch

0. 0103

.0112

.0122 .0132 .0142

.0151 .0160 .0170

.0180 .0190

.0190

.0204

.0214 .0223

.0232 .0252

.0271

,0290 ,0310

»0324

,0362 .0400

.0420 .0439

.0458

.0478 .0516 .0550

.0588

.0626

.0664

1 Equivalent angular variation expressed as a decimal part of one turn.

2 Maximum amount it is possible for new working plug and ring gages which come within the specified tolerances to vary from being flush at the small end or at the gaging notch when screwed together tight by

hand (2 times column 3+0.0010 inch)

.

3 Maximum amount it is possible for new working plug or ring gages which come within specified toler- ances to vary from being flush at the small end or at the gaging notch when screwed on reference gage tight

, , , /Column 5, Table 51+column 5, Table 52.1 by hand. { 2 J Table 53.

Corrections in diameter for errors in half angle, American National

taper pipe thread gages

Correction in diameter, E"

Error in half angle of thread in minutes, a' 8 threads WA threads 14 threads 18 threads 27 threads

per inch per inch per inch per inch per inch

1 2 3 i 5 6

Inch Inch Inch Inch Inch

1 0. 00006 0. 00004 0. 00003 0. 00002 0. 00002

2 . 00011 .00008 .00006 . 00005 .00003

3 . 00017 . 00012 . 00010 . 00007 . 00005

4 . 00022 . 00016 .00013 .00010 .00007

5 . 00028 .00019 . 00016 . 00012 .00008

6 . 00034 . 00023 . 00019 . 00015 . 00010

7.... . 00039 . 00027 . 00022 . 00017 .00012

8 . 00045 . 00031 . 00026 . 00020 . 00013

9 .00050 . 00035 . 00029 . 00022 . 00015

10.. .00056 . 00039 , 00032 . 00025 . 00017 18415°—29-
124 NATIONAL SCREW THREAD COMMISSION

Table 53.

Corrections in diameter for errors in half angle, American National

taper pipe thread gages—Continued

Error in half angle of thread in minutes, a' Correction in diameter, E''

8 threads

per inch WA threads per inch

14 threads per inch18 threads

per inch

27 threads

per inch

11.

12.

13.

14.

15.

16.

17.

IS.

19. 20.

21. 22

2324

25

26

27

28

29

30

45

Inch

0. 00062

.00067

. 00073

. 00078

.00084

.00095 .00101

. 00106

.00112

.00117

.00123

.00129

. 00134

.00140

. 00145

.00151 .00157

. 00162

.00168 .00252

Inch

0. 00043

.00047

. 00051 .00054

.00058

. 00062

. 00066

. 00070 .00074

.00078

.00082

.00086 .00089

.00093 .00097

. 00101 .00105

.00109

.00113 .00117 .00175

.00233

Inch

0.00035

.00038 .00042

.00045 .00048

.00051

. 00054 .00058

.00061 .00064

.00067 .00070

.00074

.00077 .00080

.00083

,00089

.00093

.00144 ,00192

Inch

0. 00027

.00030 .00032

.00035

.00037

.00040

.00042 .00045

.00047 .00050

.00052

.00055

.00057 .00060

.00062

.00065

.00067

. 00070

.00072

.00075

.00112

.00149

Inch

0. 00018

.00020

.00022 .00023

.00025

a' = error in half included angle of thread. E"=correction in diameter. „„ L53812 . E"= Xtan a'.

71Table 54.

Corrections in diameter for errors in lead, 60° threads

Error in Correction in diameter, E'

ieaa in

inches, p'

0. OCOOO 0.00001 0.00002 0.00003 0. 00004 0. 00005 0. 00006 0. 00007 0.00008 0. 00009

1 2 3 4 5 6 7 8 9 10 11

Inch Inch Inch Inch Inch Inch Inch Inch Inch Inch

0.00000 0.00000 0. 00002 0. 00003 0. 00005 0. 00007 0. 00009 0. 00010 0. 00012 0. 00014 0. 00016

.00010 .00017 .00019 .00021 .00023 .00024 .00026 .00028 .00029 .00031 .00033

.00020 .00035 .00036 .00038 .00040 .00042 .00043 .00045 .00047 .00048 .00050

.00030 .00052 .00054 .00055 .00057 .00059 .00061 .00062 .00064 .00066 .00068

.00040 .00069 .00071 .00073 .00074 .00076 .00078 .00080 . 00081 .00083 .00085

.00050 .00087 .00088 .00090 .00092 .00094 .00095 .00097 .00099 .00100 .00102

.00060 .00104 .00106 .00107 .00109 .00111 .00113 .00114 .00116 . 00118 .00120

g .00070 .00121 .00123 .00125 .00126 .00128 . 00130 .00132 . 00133 .00135 .00137

.00080 .00139 .00140 .00142 .00144 . 001 15 .00147 . 00149 .00151 .00152 .00154

.00090 .00156 .00158 .00159 .00161 .00163 .00165 . 00166 .00168 .00170 .00171

.00100 .00173 .00175 .00177 .00178 .00180 .00182 .00184 .00185 .00187 .00189

.00110 .00191 .00192 .00194 .00196 . 00197 .00199 .00201 . 00203 .00204 .00206

.00120 .00208 .00210 .00211 .00213 . 00215 .00217 .00218 .00220 .00222 .00223

.00130 .00225 .00227 .00229 .00230 .00232 .00234 .00236 .00237 .00239 .00241

.00140 .00242 .00244 .00246 .00248 .00249 .00251 .00253 .00255 .00256 .00258

.00150 .00260 .00262 .00263 .00265 .00267 .00268 .00270 .00272 . 00274 .00275

.00160 .00277 .00279 .00281 .00282 .00284 . 00286 .00288 .00289 .00291 .00293

.00170 .00294 .00296 .00298 .00300 .00301 .00303 .00305 .00307 .00308 .00310

.00180 .00312 . 00313 . 00315 .00317 .00319 .00320 .00322 .00324 .00326 .00327

.00190 .00329 .00331 .00333 .00334 .00336 . 00338 .00339 . 00341 .00343 .00345

i, .00200 .00346 .00348 . 00350 .00352 .00353 . 00355 .00357 .00359 .00360 .00362 p'= error in lead. E'= correction in diameter. E'= 1.732 p'.
GAGES FOE PIPE THREADS 125

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CO O O i-H i-l «5 CO >C «5 CM CO " CO rH CD l> OS

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CO CO CO CO OS

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CM CM CD O t~ rH rH CO OS O *o rH 00 00

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go £-2

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CCJ ,H ,_( ,H .-IjHrHrH §5

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CM rH m CO
126 NATIONAL SCREW THREAD COMMISSION

g o g o g g g g §§§§§ ssss

,S cm' cm cm cd co co co co

43 S

9 Pi H

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lOiOON OO O i-i CM

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CM CM CM CM CMCMCMCN

Co co CO CO CO COCOCDCD ^ io io >o jo ^2|2j2|2 C^O>050C5 Oi O)

>•«< CO C5 '-i coiot-^oS HHHIN CM CM CM CM

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bo a goo CO CO 00 ^ S £h 2 cm" CM CM CM CM

-«S tO iO CO CM

3 ~ bcco

bo o <= iCiOt^OO O O CM CO

?p CM CM lO 00 HU5 00H

^OOCOCOOO -<*<a>Tj<0

io >o io Tt< co co co y Oi OS OJ OJ Ci OS Cb o

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oioiom io io io >o

<S lO CM t- CM CM CM

CM S OOOO QQOO ,loioioio O O © O OOOO to to to u5

' £h ^ £2 £3 S3 2 £2 N

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00 00 00 00 00COCOCO

dodo dodo

§2

CP h3 ^.9
AMERICAN NATIONAL WOOD SCREW SIZES 127

SECTION VII. WOOD SCREWS

This specification summarizes the results of the standardization of

wood screws by the manufacturers in cooperation with the Bureau of

Standards and the technical committee on builders' hardware of the

Federal Specifications Board. It has been officially adopted by the

Federal Specifications Board for the use of all departments and

1 independent establishments of the Government in the purchase of

wood screws, and published as Circular No. 140 of the Bureau of

Standards, second edition, issued October 8, 1927.

The former difference of 0.013165 inch in diameter, used as a basis

for the arithmetical progression of the numbering system, has been

discarded in favor of a difference of 0.013 inch (even) as established

by the commission for machine screws. This provides interchangeability for the numbered sizes of machine screws and wood screws

in connection with articles that may be fastened either to metal or wood.

Flat, round, and oval head types are covered in the specification.

The numbered sizes of wood screws run consecutively from No.

(0.060 inch) to No. 24 (0.372 inch), omitting Nos. N13, 15, 17, 19,

21, 22, and 23.

1. GENERAL SPECIFICATIONS

(a) Types.—Wood screws shall be furnished in three types;

namely, flat, round, or oval head, as specified.

(&) Material and Workmanship.—Wood screws shall be made

of steel or brass, as specified, and shall be free from any defects which

would affect their serviceability.

(c) Measurement of Lengths.—The length of all screws shall be

measured from the largest diameter of bearing surface of the head to the extreme end of the point measured parallel to the axis of the screw.

(d) Measurement of Diameters.—The diameter shall be measured on the body of the screw under the head.

(e) Tolerance on Diameter.—The maximum variation on diameter permitted is from +0.004 to —0.007 inch.

(J) Tolerance on Number of Threads per Inch.—The maximum variations in the number of threads per inch permitted are plus or minus 10 per cent.

(g) Points.—Standard screws shall be furnished with gimlet points.

Cone and diamond pointed screws are special.

Qi) Finish.—Wood screws shall be furnished plain, uncoated, unless

blued, nickel plated, or other special finish is specified.

(i) Head Proportions and Length of Thread.—The proportions of the head and length of thread shall be as indicated in Figure 32

and Tables 56, 57, and 58.
NATIONAL SCREW THREAD COMMISSION

MAX. W s a?*

Vrim. ©

MAKH

MAX. J MIN. J MAX.T

MiN.T

2.0H-A - 0.O03

1.96A - 0.013

0.619A-0.002

0.I82A+0.020

0.1©H-A + O0»O

0.2©SA-0.002

O.I92A- O.OOS

Tl

-N

MAX.©

Mm.x>

MAX. H

MIN.M

MAX. J M IN, J MAX. T

MtN, T

I.813A

o.esH>A

0. 162A

O.ieMA

O.S62A

o.^ee*

- ©\OIO

+ O.OIS

+ O.OG5

O.OZQ

O.OlO

O.Ol7

+ o,o»a

X

*-H

MAX.D * Mlli.D * MAX. H « MAX. J * MIN.O « MAX. T « Mm.T * MAX. F a MIN.F s

2.0HA - 0.003

l.96A> - CO 13 0.619A- 0.002

0.162A+0.020

0.16MA+ O.OIO O.S5SA- 0O03

O.H-60A-0.003

O3O4-A*O.O03

0.2©aA-O.OOl

Fig. 32.

Wood screws
AMERICAN NATIONAL WOOD SCREW SIZES 129

Table 56.

Head proportions of fiat-head wood screws

v

A D H J T

Nominal size Head diameter Height Width of slot Depth of slot Diameter of head, Maxi- Mini- mum Maxi- Mini- Maxi- Mini- mum mum mum mum mum mum

Inch Inch Inch Inch Inch Inch Inch Inch

o 0. 060 0. 119 0. 105 0. 035 0. 031 0. 020 0. 015 0. 010

l .073 . 146 . 130 .043 .033 .022 .019 .012

. 086 . 172 . 156 .051 .036 .024 .023 .015

3 . 099 . 199 . 181 . 059 .038 .026 .027 .017

4 . 112 .225 .207 .067 .040 .028 .030 .020

5 .125 .252 .232 .075 .043 .031 .034 .022

6 . 138 .279 .257 .083 .045 .033 .038 .024

7 . 151 .305 .283 .091 .047 .035 .041 .027

8 . 164 .332 .308 . 100 .050 .037 .045 .029

9 .177 .358 .334 .108 .052 .039 .049 .032

10 .190 .385 .359 .116 .055 .041 .053 .034

11 .203 .411 .385 .124 .057 .043 .056 .037

12 .216 .438 .410 .132 .059 .045 .060 .039

14 - .242 .491 .461 .148 .064 .050 .068 .044

16 - .268 .544 .512 .164 .069 .054 .075 .049

18 .294 .597 .563 .180 .074 .058 .083 .054

20 .320 .650 .614 .196 .078 .062 .090 .059

24 .372 .756 .716 .228 .088 .071 .105 .069 Table 57.

Head proportions of round-head wood screws A D H J T

Nominal size Head diameter Height of head Width of slot Depth of slot Diameter Maxi- mum

Mini- mumMaxi- mumMini- mumMaxi- mumMini- mumMaxi- mum

Mini- mum

- Inch

0. 060 Inch

0. 113 Inch

0. 099 Inch0. 053 Inch0.042 Inch

0.031 Inch0. 020 Inch0.039 Inch0. 029

1 - .073 .138 .122 .061 .051 .033 .022 .043 .033

2 .086 .162 .146 .070 .059 .036 .024 .048 .036

3 .099 .187 .169 .193

.078 .086

.067 .038 .026 .053 .040

4 .112 .211 .075 .040 .028 .058 .043

5 — .125 .236 .217 .095

.103

.083 .043 .031 .062 .047

6 .138 .260 .240 .091 .045 .033 .067 .050

7 —

-

.151 .285 .264 .111 .099 .047 .035 .072 .053

8 - .164 .309 .287 .119 .107 .050 .037 .076 .057

9 .177 .334 .311 .128 .115 .052 .039 .081 .060

10 .190 .359 .334 .136 .124 .055 .041 .086 .064

11 — .203 .383 .358 .144 .132 .057 .043 .090 .067 12— .216 .408 .382 .152 .140 .059 .045 .095 .071

14. .242

.268

.457 .429 .169 .156 .064 .050 .105 .078

16 .506 .476 .185 . 172 .069 .054 .114 .085

18 .294 .555 .523 .202 .188 .074 .058 .123 .092

20 .320 .604 .570 .219 .205 .078 .062 .133 .099

24 .372 .702 .664 .252 .237 .088 .071 .152 .113
130 NATIONAL SCREW THREAD COMMISSION

Table 58.

Head pro-portions of oval-head wood screws

IN UililllcU olio

A D H J T F F+H

Diameter

Head diameter Height

nf hi pari Width of

slot Depth ofslot Height of oval Maxi- mum

Mini- mum

Maxi- mum

Mini- mum

Maxi- mumMaxi- mumMini- mumMaxi- mumMini- mumMaxi- mumMini- mum

Inch Inch Inch Inch Inch Inch Inch Inch Inch Inch Inch Inch

0. 060 f\ 1 1Q u. ii» 105 0. 035 0. 031 n non U. uzu U. UoU n not;

U. UZO 0. 021 0. 015 0. 056 0. 041

073 130 . 043 . Voo 022 . Uoo 031 no* mo !068 052

2 !o86 . 172 . 156 !051 . 036 . 024 . 045 . 037 . 029 . 022 !080 !062

3 .099 .199 .181 .059 .038 .026 .052 .043 .033 .026 .092 .074

4 .112 .225 .207 .067 .040 .028 .059 .049 .037 .029 . 104 . 084

5 125 .252 .232 . 075 .043 .031 .067 .055 .041 .033 . 116 . 095 \m .279 .257 !083 .045 .033 .074 .060 .045 .036 '.128 !l05

7 .151 .305 .283 .091 .047 .035 .081 .066 .049 .039 .140 .115

8. .164 .332 .308 .100 .050 .037 .088 .072 .053 .043 .153 .127

9 .177 .358 .334 .108 .052 .039 .095 .078 .057 .046 .165 .137

10 . 190 .385 .359 . 116 .055 .041 .103 .084 .061 .050 . 177 .148

11 .203 .411 .385 .124 .057 .043 .110 .090 .065 .053 .189 . 158 12 .216 .438 .410 .132 .059 .045 . 117 .096 .069 .057 .201 .169

14 .242 .491 .461 .148 .064 .050 .132 .108 .077 .064 .225 .191

16 .268 .544 .512 .164 .069 .054 . 146 .120 .084 .071 .248 .212

18. — .294 .597 .563 .180 .074 .058 . 160 .132 .092 .078 .272 .233

20.. .320 .650 .614 . 196 .078 .062 .175 .144 .100 .085 .296 .254

24.. .372 .756 .716 .228 .088 .071 .204 .168 .116 .099 .344 .297

(j) Included Angle.—The included angle of the head on flat and

oval head screws shall be 82°, with permissible variations of +0°

and -2°.

2. THREAD SERIES

The numbered screw sizes, basic and limiting diameters, and

threads per inch given in Table 59 are standard.

Table 59.

American National wood screw standard size numbers, diameters, and

Number of screw

12

3

4

56

78

9

Threads

per inch

32

Diameter

Basic

Inch

0.060

.073

112

125

138

151 164 177

Maxi- mum

Inch

0.064 .077

.090

.103

.116 .129 .142

.155

.168

.181

Mini- mum

Inch

0. 053

.066

.079 .092 .105

.118

.131 .144

.157

.170

Number of screw

10

1112

14

16

182024

Threads

per inch

Diameter

Basic

Inch

0. 190 .203 .216

.242

294

320 372

Maxi- mum

Inch

0. 194 .207

.220

.246

.272

324 376

Mini- mum

Inch

0. 185 .196 .209

.235

.261

.287

.313 .365

3. TOLERANCES ON LENGTH

(a) Flat and Oval Head Screws.—The maximum variations per- mitted in the length of flat and oval head screws are given in Table 60.

(6) Round-Head Screws.—The maximum variations permitted in the length of round-head screws are given in Table 61.
AMERICAN NATIONAL WOOD SCREW SIZES

Table 60.Tolerances on length of fiat and oval head screws 1 131

Nominal length in inches Minus

tolerance Nominal length in inches Minus

tolerance H

Inch

0. 031 .033

.035

.037

.039

.041

.043

.048 .052

.056

2 Inch

0.060

. 064

'.068 .072 .076

.084

.092

.101 .109

H 2y2 % 2% % 3 % zy2 4.. IX — m5 1H

i Plus tolerance=0. Table 61.

Tolerances on length of round-head screws 1

Screw numbers

Nominal length in inches

1 2 3 4 5 6 7 8

Inch

0.064

.065

Inch

0.071

.073 .075

Inch

0.077

. 079

.081 .083 .085

Inch

0.084

.086 .088

.090 .092

.094

.096

Inch

0. 090

.092 .094

.096

.098

.100

.102

.106 .110

Inch Inch Inch Inch

Ys 0.099

.101

.103

.105 .107

.109

.113 .117

0. 105 .107

.109

.111 .113 .115

.119

.123

.127

.131

.135

.139

0.112

.114 .116

.118

.120

.122

.126 .130

.134

.138 .142

.146

0. 118 .120

.122

.124

.126

.128

.132

.136

.140

.144

.148 .152

.156

Yi%

ZA

v%1U

iy2 M22M

2Y2 2H

Nominal length in inches Screw numbers

9 10 11 12 14 16 18 20 24 %

Inch

0. 127 .129

.131 .133

.135 .139

.143

.147

.151 .155 .159

.163

.167

Inch

0. 133 .135

.137

.139

.141 .145 .149

.153 .157

.161 .165

.169

.173

.181

Inch Inch Inch Inch Inch Inch Inch

Ys —

-

6. 142 .144 .146

.148 .152

.156 .160

.164

.168 .172

.176 .180

.188

0. 148 .150

.152

.154 .158 .162

.166

.170

.174

.178

.182

.186

.194 .202

% 0. 163 .165

.167

.171 .175

.179 .183

.187

.191 .195 .199

.207

.215

.223 .231

y8

l 0. 180 .184 .188

.192

.196 .200

.204

.208 .212

.220 .228

.236 .244

V4. 0. 198 .202

.206 .210

.214 .218

.222

.226

.234 .242

.250

.258

iy2

0. 215 .219

.223 .227

.231

.235 .239 .247

.255

.263

.271

i%

22H

2HM.—-.

3 0.265 .273

.281 .280

.297

3H

4 —

5

i Plus tolerance =0. Minus tolerances as given in body of table.
132 NATIONAL SCREW THREAD COMMISSION

4. AMERICAN NATIONAL STANDARD SIZES OF WOOD SCREWS

(a) Steel Screws.—The standard sizes of steel screws are given

in Table 62.

(b) Brass Screws.—The standard sizes of brass screws are given

in Table 63. Table 62.

Standard sizes of steel screws

[F, flat head; R, round head; O, oval head]

Lengths (inches) No.

diameter, 0.060 inch

No. 1 diameter, 0.073 inchNo. 2 diameter, 0.086 inchNo. 3 diameter, 0.099 inchNo. 4 diameter, 0.112 inchNo. 5 diameter, 0.125 inch

No. 6 diameter, 0.138 inchNo. 7 diameter, 0.151 inchNo. 8 diameter, 0.164 inch H FR

FR

FR

FR

FR

FR

FR

FR

FR

FR

FR

FRO

FR

FR

FRO

FRO

Vs FR

FRO

FRO

FRO

FR

FRO

FR

FR

FR

FRO

FRO

FRO

FR

FRO

FRO

FRO

FRO

FR

FR

FR

FR

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FR

FR

FR

FR

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

y2 y6 FR

FR

FR

FR

FRO

FRO

FR

FR

FR

FR

%

%

iVi

\y2 i%._

2_. FR

FR

FR

FR

2Al 2y2 2%.-

Lengths (inches)

No. 9 diameter, 0.177 inch

No. 10 diameter, 0.190 inchNo. 11 diameter, 0.203 inchNo. 12 diameter, 0.216 inchNo. 14 diameter, 0.242 inchNo. 16 diameter, 0.268 inch

No. 18 diameter, 0.294 inchNo. 20 diameter, 0.320 inchNo. 24 diameter, 0.372 inch H~- FR

FR

FRO

FRO

FRO

FRO

FRO

FRO

FR

FR

FR

FR

FR

FR

FR

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FR

FR

FR

FR

FR

k - —

FR

FR

FR

FRO

FRO

FRO

FRO

FRO

FR

FR

FF

F

FR

FR FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FR

FR

FR

FR

k

A7 FR FRO

FRO

FRO

FRO

FRO

FRO

FRO

FR

FR

FR

FR

F

F

l FR

FR

FRO

FRO

FRO

FR

FR

FFR

FR

FR

F

F

IX - FR

FRO

FRO

FRO

FFR

FFR

F

F

FF

iy2 FRO

FRO

FRO

FFR

FF

F

F

F

F

m22M- —

2^— -

2H - 3 FF

FF

F

3H

44H

5
AMERICAN NATIONAL BOLT AND NUT PROPORTIONS 133

Table 63.

Standard sizes of brass screws

[F, flat head; R, round head; O, oval head]

Lengths (inches) No.

diameter, 0.060 inch

No. 1 diameter, 0.073 inch

No. 2 diameter, 0.086 inchNo. 3 diameter, 0.099 inch

No. 4 diameter, 0.112 inchNo. 5 diameter, 0.125 inchNo. 6 diameter, 0.138 inchNo. 7 diameter, 0.151 inch M FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

ys FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

H FRO

FRO

FRO

FRO

FRO

FRO

FRO

y8 H

% - i\V>

Lengths (inches) No. 8 diameter, 0.164 inch

No. 9 diameter, 0.177 inchNo. 10 diameter, 0.190 inch

No. 11 diameter, 0.203 inchNo. 12 diameter, 0.216 inch

No. 14 diameter, 0.242 inch

No. 16 diameter, 0.268 inch

No. 18 diameter, 0.294 inch

Yt FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

Vs FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FRO

FR

FR

% FR

FR

FR

FR

FR

FR

FR

FR

FR

FRO

FR

FRO

FRO

FRO

FRO

FRO

FR

FR

FR

F

Ys

1 FRO

FRO

FRO

FRO

FRO

FR

FR

FR

F

IK

iy2 i*A

2 FF

F

FF

FF

FF

F —- - -

2y2 33H

SECTION VIII. AMERICAN NATIONAL SCREW, BOLT, AND

NUT PROPORTIONS

Section VIII A. Wrench Head Bolts and Nuts, and Wrench Openings

A project to which the commission gave early attention was the

standardization of bolt and nut proportions, particularly as to the

widths across flats, because of the desirability of reducing the number

of sizes of bar stock, dies, and wrenches necessary. A subcommittee

of the commission and subcommittee No. 2 of the Sectional Committee on the Standardization of Bolt, Nut, and Rivet Proportions,

organized under the procedure of the American Standards Association, worked in close cooperation in developing the standards for

wrench-head bolts and nuts which are given below. This standard,

in substantially the same form, is published as report No. B 18b-1926

of the American Standards Association.

These sizes of bolt heads and nuts are intended to supersede all existing standards which have grown up for commercial standard bolt

heads and nuts. Through simplification of outside dimensions of

bolt heads and nuts by eliminating thirty-second-inch sizes, and
134 NATIONAL SCREW THREAD COMMISSION

elimination of sizes little used, it has been possible to reduce the

number of wrench openings required.

In all cases the basic widths across flats of bolt heads and nuts are taken as maximum sizes and the tolerances on bolt heads and nuts

are minus only. The minimum wrench openings are made to provide

a positive clearance between maximum nut and minimum wrench,

and the tolerances on wrench openings are plus only. This insures a fit of the wrench to the bolt head and nut, whereas the tolerances

allowed are as great as possible without causing the deformation of the corners of bolt heads or nuts by the wrenches.

1. GENERAL REQUIREMENTS

(a) Workmanship.—It is recommended that workmanship be

compatible with the type and grade of product, and class of fit and

of finish specified; and that the product be free from abnormal

scale, fins, seams, or other defects.

(b) Screw Threads.—The form of thread profile is the American

National form and the diameters and threads per inch are those

specified as the American National coarse-thread series, or the

American National fine-thread series, as given in Section III. 21 (c) Body Diameters.—The dimensions and tolerances for body

diameter of bolts and screws are given in Tables 64 and 65.

(d) Tolerance on Length.—The length of all bolts and screws up to and including 6 inches in length does not vary from the nominal

length by more than ± %i inch; and the length of all bolts and screws more than 6 inches in length does not vary from the nominal length

by more than ± Ke inch.

(e) Bolt and Screw Lengths.—Bolts and screws, except for

special requirements, should be ordered in the following increments

of length:

Length Increment

Inches Me to H

Over Vz to IKOver 1H to m Over 3K to 6 Over 6 to 10 Over 10

InchesMeH

M

H

l2

2. MACHINE BOLTS

Machine bolts are regularly furnished one-fourth inch and

over in diameter and with hexagon or square heads. They are furnished with square or hexagon nuts. They are threaded for a length dependent upon the diameter and length.

j*L M See Appendix 6, p. 241, for common practice as 2 to thread series and class of fit.
AMERICAN NATIONAL BOLT AND NUT PROPORTIONS 135

The length of a machine bolt is the measurement from the extreme

point to the bearing surface of the head. The length of thread is measured from the extreme point to the last perfect thread.

The tops of bolt heads are flat and chamfered ; the maximum angle

of chamfer with the top surface is 30°, and the diameter of the top

flat circle is from 85 to 100 per cent of the width across flats. The width across flats of bolt heads is measured at the widest

point. The taper of the sides of bolt heads does not exceed 4°. Bolt heads are concentric with the body within a tolerance of 3

per cent of the width across flats. The minimum lengths of thread, unless otherwise specified, are given in Table 66. The thickness of the head is the distance from the top to the bearing surface.

(a) Rough and Semifinished Bolts.—Rough bolts are made by

cold or hot pressing, punching, or forging. They are threaded but

not machined.

Semifinished bolts are those which meet the tolerances prescribed

without regard to the amount of machining needed to meet such

tolerances, except that the bearing surfaces are finished smooth.

The dimensions of rough and semifinished bolts are given in Table

67.Rough and semifinished bolt heads are at right angles to the body

within 3°.

(b) Finished Bolts.—Finished bolts and nuts are machined all over, and threaded.

The dimensions of finished bolts are given in Table 68. Finished bolt heads are at right angles to the body within 2°. All finished bolts are washer faced. The thickness of the washer

face is about one sixty-fourth inch. The diameter of the bearing surface of the washer face is equal to the width across flats within

plus or minus 5 per cent.

3. TAP BOLTS

Tap bolts are the same as machine bolts, except that they are threaded to the head, and they may be used interchangeably. Tap

bolts are regularly furnished in the coarse thread series one-fourth

inch and over in diameter, without nuts, and with square or hexagon heads. The length of bolt is measured from the extreme

point to the bearing surface of the head.

4. NUTS

Nuts are commonly either hot forged, cold punched, or machined

from bar stock.

The tops of regular square and hexagon nuts when not castellated,

of jam nuts, square and hexagon machine screw nuts, and of hexagon
136 NATIONAL SCREW THREAD COMMISSION

light nuts when not castellated, are flat and chamfered; the maximum angle of chamfer with the top surface is 30°; and the diameter

of the top flat circle is from 85 to 100 per cent of the width across flats. The width across flats of nuts is measured at the widest point.

The taper of sides of nuts does not exceed 4°. All finished hexagon and square regular nuts, castellated nuts,

and hexagon light nuts are washer faced. The thickness of the

washer face, including that of jam nuts having a washer face, is about one sixty-fourth inch. The diameter of the bearing surface of the washer face is equal to the width across flats within plus or minus

5 per cent. The thickness of the nut is the distance from the top to the bearing surface.

(a) Rough and Semifinished Regular Nuts.—Rough nuts are made by cold or hot pressing, punching, or forging. They are threaded but not machined.

Semifinished nuts are those which meet the tolerances prescribed

without regard to the amount of machining needed to meet such

tolerances, except that the bearing surfaces are finished smooth.

The dimensions of rough and semifinished square and hexagon

regular nuts are given in Table 69. Semifinished nuts are faced on the bearing surface and are at right

angles to the axis of the threaded hole within 3°.

(&) Finished Regular Nuts.—The dimensions of finished square

and hexagon regular nuts are given in Table 70. The axis of the threaded hole is at right angles to the washer face

within a tolerance of 2°.

(c) Castellated Nuts.—The dimensions of castellated nuts are given in Table 71. The axis of the threaded hole is at right angles to the washer face

within a tolerance of 2°.

(d) Finished and Semifinished Jam Nuts.—The dimensions of finished and semifinished jam nuts are given in Table 72. Jam nuts

are either single or double chamfered as specified. If a single chamfer

is specified, the opposite side is washer faced.

The axis of the threaded hole is at right angles to the washer or

finished face within a tolerance of 2°.

(e) Hexagon Light Nuts.—The dimensions of hexagon light

nuts are given in Table 73.

(J) Hexagon and Square Machine Screw Nuts and Square

Stove Bolt Nuts.—The dimensions of hexagon and square machine

screw nuts and square stove bolt nuts are given in Table 74. Machine screw nuts, when made from hexagon bar stock, are faced on the bearing surface and this surface is at right angles to the axis of the threaded hole within 5°.
AMERICAN NATIONAL BOLT AND NUT PROPORTIONS 137

5. HEXAGON-HEAD CAP SCREWS

Cap screws are usually manufactured by upsetting or by machining.

They are usually threaded definite lengths for each diameter irre- spective of length of screw. They are furnished without nuts. The

smallest diameter regularly furnished is one-fourth inch.

The length of cap screws is measured from the bearing surface of

s the head to the extreme point. The length of thread is measured from

the extreme point to the last perfect thread.

The head is at right angles to the body within 2°, and concentric

with the body within a tolerance of 3 per cent of the width across flats. Cap screws 1 inch in length and under are threaded from the

extreme point to the head. For cap screws longer than 1 inch, the

minimum length of thread is one and one-half times the diameter

plus one-fourth inch.

The dimensions of finished hexagon-head cap screws are given in

Table 75. The tops are smooth, flat, and chamfered; the maximum angle of

chamfer with the top surface is 30° ; and the diameter of the top flat circle is from 85 to 100 per cent of the width across flats. All finished hexagon cap screw heads are washer faced. The thick- ness of the washer face is about one sixty-fourth inch. The diameter

of the bearing surface of the washer face is equal to the width across

flats within plus or minus 5 per cent. The thickness of the head is the distance from the top to the bearing surface.

6. WRENCH OPENINGS

Wrench openings for open-end wrenches are given in Table 76. The sizes given in the table for the maximum and minimum columns

are sizes of "go" and "not go" gage blocks used for inspecting

wrenches and are not product sizes. Wrenches should be marked with the basic width across flats (maximum width of nut), as shown in column 1.
138 NATIONAL SCREW THREAD COMMISSION

Table 64.- -Body diameters of bolts and screws,

series American National coarse-thread

Class 1, loose fit

Maxi- mum

Mini- mum

Class 2, free fit*; class 3, medium

fit; class 4, close

fit

Maxi- mum

Mini- mum

Class 2, free fit, threaded

parts of unfinished, hotrolled material Mini- mum

1__

2__ 3..

4__

5_.

6._

8__

10.

12. H-%-

Via

Vi- HbH-U.

7A1__ m

m

m

w2.- 2H

2\ 2 234 3„

Inches

0. 0723 .0852

.0981

. 1110 .1240

.1369

.1629

.1887

.2147

.2485 .3109

.3732

.4354 .4978

.5601 .6224

.7472

.8719 .9966

1. 1211

1. 2461

1. 4956

1. 7448

1. 9943 2.2443

2. 4936

2. 7436

2. 9936

Inches

0. 0671 .0796

.0919 .1042 .1172

.1293

.1553

.1795

.2055 .2383

.2995 .3606

.4214

.4830 .5443

.6054

.7288

.8519 .9744

1. 0963

1. 2213 1.4666

1. 7110

1. 9575

2. 2075

2. 4528 2.7028

2. 9528

Inches

0. 0730

.0860

.0990

.1120

.1250

.1380

.1640 .1900

.2160 .2500

.3125

.3750

.4375 .5000

.5625 .6250

.7500

.8750

1.0000

1. 1250 1.2500 1.5000

1. 7500 2.0000

2. 2500 2.5000

2. 7500

3. 0000

Inches

0.0692

.0820

.0946 .1072 .1202

.1326

.1586

.1834

.2094 .2428

.3043 .3660

.4277

.4896 .5513

.6132 .7372

.8610

1. 2330

1. 4798

1. 7268

1. 9746

2.2246

2. 4720

2. 7220

2. 9720

Inches

0. 0678

.0804

.0928 .1052

.1182

.1304

.1564

.1808

.2068

.3011 .3624

.4235 .4852

.5467

.6080

.7316 .8550

.9778

1. 1002

2252 4710

7162

2. 2132

2. 4592 2.7092

2. 9592

i For class 2, free fit, these minimum values apply only to semifinished and finished bolts and screws. Table 65.

Body diameters of bolts and screws, American National fine-thread

series

Sizes

Class 1, loose fit

Maxi- mum

Mini- mum

Class 2, free fit; class 3, medium

fit; class 4, close

fit Maxi- mum

Mini- mum

Siz6S Class 1, loose fit

Maxi- mumMini- mum

Class 2, free fit; class 3, medium

fit; class 4, close

fit Maxi- mum

Mini- mum

0__

1. . 2__

3__ 4__

5_.

6.. 8._

10 _ 12. U5/l6 %.

Me

Clinch

0. 0593 .0723

.0853 .0982

.1111 .1241 .1370

.1629

.3112

.3737

.4360

Inch

0.0545

.0673

.0801 .0926

.1049 .1177

.1302

.1557 .1813 .2062

.2402

.3020

.3645

.4258

Inch

0.0600

.0730

.0860 .0990 .1120

.1250

.1380 .1640

.1900 .2160

.2500

.3125 .3750

.4375 .5000

Inch

0.0566

.0694

.0822

.0950

.1076 .1204

.1332 .1590

.1846

3059

3684

4303

9 ie H-

%-

Hi__ iHm

m

2__ 2H

2\i 2H

3__

Inches

0. 5609 .6234 .7482

.8729

.9979

1. 1226

1. 2476

1. 4976

1. 7472

1. 9972

2. 2466

2. 4966

2. 7466

2. 9966

Inches

0. 5495 .6120

.7356

.8589

1. 1068

1. 2318

1. 4818

1.7288

1. 9788 2.2244

2. 4744

2. 7244

2.9744

Inches

0. 5625 .6250

.7500 .8750

1.0000

1. 1250 1.2500

1.5000

1. 7500 2.0000 2.2500

2. 5000

2.7500 3.0000

Inches

0. 5543 .6168

.7410 .8652

.9902

1. 1138 1.2388

1.4888

1. 7372

1. 9872

2. 2348

2. 4848

2. 7348 2.9848
AMERICAN NATIONAL BOLT AND NUT PROPORTIONS 139

Table 66.

Minimum length of threaded portion of machine and tap bolts

Diameter of bolt, D (inches)

Length of bolt, L (inches) H Me % Vl6 H He

Length of threaded part, I

1 2 3 4 5 6 7

1 to InchU

14

l

Inch

' A

%

Inches%

1

Inches

Vs Inches

1 Inches

1 m to 2 1 1 1 2Vs to 2Y2

i 1 1 1 1 2% to 3 l 1

' 1 1 1 1 ?¥% to 4 l 1 Mm 1HM

VA

1H

1H

2

XMH iys to 8 l 1 8ys to 12 l 1 m 12M to 20 l 1 2

Diameter of bolt, D (inches)

Length of bolt. L (inches) H 3A 7A 1 m m

Length of threaded part, I

1 8 9 10 11 12 13

lto \y2 -— .... Inches1Hm

m

2

Inches Inches Inches Inches Inches

iy» to 2 m

m

i%

2

1%

1%

1%

1*A

2

2H to 2Y2 - 1U 2% to 3 2 2K 3H to 4 2 2Yi 2A 2y2 mto 8 2A

2y2 3 sy8 to 12 2H 3 VA Mi to 20 2 2Y2 3 *A

Note.—Machine bolts under 1 inch in length are threaded to the head. Machine bolts of any diameter, over 20 inches in length, and bolts over 1A inches in diameter, if length permits, are threaded a length equal to three times the diameter unless otherwise specified, 18415°—29 10
140 NATIONAL SCREW THREAD COMMISSION

Table 67.

Dimensions of rough and semifinished square and hexagon machine and

tap belt

t p

" in o

oo Q

)T

^

"Width across flats Minimum width

across corners Height

Maxi- mumMini- mum Hexagon Square Nominal Maxi- mum

Mini- mum

H-HHz/±- Hl__ mm

m2__ 2H

2%

Inches

0. 3750

.5000

.5625 .6250

.7500

.8750

.9375

1. 1250 L 3125 L 5000

1.6875

1. 8750

2.2500

2. 6250

3.0000

3. 3750

3. 7500

4. 1250 4.5000

Inches

0. 363 .484

.544

.603 .725

.906

1.088

1.269

1. 450 L 631 1.813

2. 175

2. 538 2.900

3. 263

3. 625

3. 988

4. 350

Inches

0.414 .552

.620

.687 .827

.966

1.033 1.240

1.447

1.653 1.859

2. 067

2. 480

2. 893

3. 306

3. 720

4. 133 4.546

4.959

Inches

0.498

.665 .747

.828

1. 163 1.244

1.494 L 742

1. 991

2. 239 2.489

2.986 3.485

3. 982

4. 480

4. 977

5. 476

5. 973

Inches

2^4

2 ^4

Yl2^2

2%2

11%2 1^2

iH

12^2

i 5 %4

2

Inches

0.188 .220

.268

.316

.348

444

524 620

.780

.876

1.036 L 196

1. 388

1.548

1. 708

1.885

2. 060

Inches

0. 156 232

278

354 400

476

.720 .812

.964

1.116

1. 3C0

1. 452

1.604

1. 773 1.940
AMERICAN NATIONAL BOLT AND NUT PROPORTIONS 141

Table 68.

Dimensions of finished square and hexagon machine and tap bolt heads

Width across flats

Maxi- mum

Mini- mum

Minimum width

across corners

Hexagon Square

Height

Nominal Maxi- mum

H-MeH7/n.

K7A1_. mm

mIH2—

2U

2Vfe 2%

3_.

Inches

0. 4375 .5625

. 6250 .7500

.8125 .8750

.9375

1. 1250

1. 3125

1. 5000

1. 6875

1. 8750

2. 2500

2. 6250

3. 0000

3. 3750

3. 7500

4. 1250

4. 5000

Inches

0.428

.552

.613

.737

.799

.922

1. 108 1.293 1.479

1.665

1.850 2.222

2.593 2.964

3. 335 3.707

4. 078

4. 449

Inches

0. 488 .629

,911

1.051

1. 263

1. 474

1. 686 1.898

2. 109

2. 533

2. 956

S. 379

3. 802

4. 226

4. 649

5. 072

Inches

0. 588 .758

.842

1. 012

1. 097

1. 182

1. 266

1. 521

1. 775

2.031 2.286

2. 540

3.051

3. 560 4.070

4. 579

5. 090

5. 599

6. 108

Inches

2 H2

2%2

lYs lMe m

Wis

m2H5 2%

Inches

0. 194 .242

.289 .337

.385

.433

.481 .576

.672

.768

.863

.959

1. 150

1. 341 1.533

1. 724

1. 915

2. 106 2.298
142 NATIONAL SCREW THREAD COMMISSION

Table 69.

Dimensions of rough and semifinished square and hexagon regular nuts F00 — °L

^30°

H

B

HMe

H-^1

%6

94- 1__ m1*2 194 2..

3*4 2H3„

Width across flats

Maxi- mum

Inches

0. 4375 .5625 .6250

.7500

.8125

.8750

.9375

1.1250

1. 3125 1.5000

1.6875

1. 8750

2. 2500

2. 6250 3.0000

3. 3750

3. 7500

4. 1250 4.5000

Mini- mum

Inches

0.425

.547 .606

.728

.847 .906

1.088

1.269

1. 450

1.631

1. 813

2. 175

2. 538 2.900

3. 263

3. 625

3. 988

4. 350

Minimum width

across corners

Hexagon

Inches

0. 485 .624

.691 .830

.966

1.033

1. 240

1. 447

1. 653

1.859

2. 067 2.480

2.893

3. 306

3. 720

4. 133

4. 546 4.959

Square

Inches

0. 584

.751 .832

1.000 L 082 L 163 1.244

1. 494 1.742

1.991

2. 239 2.489

2. 986 3.485

3. 982 4.480

4. 977

5. 476

Thickness

Nominal

Inchesm*

%

Me

3 Hi

4 %4%

11%2

1

5/16 1%

1%

1 3 ^2

23/16 213/§2 2%

Maxi- mum

Inches

0.235

.283 .346

.394

.505

.569 .680

.792

.903

1.030 L 126 1.349

1. 571

1. 794 2.017

2.240

2. 350 2.685

i Manufacturers' standard adopted by the Bolt, Nut, and Rivet Manufacturers Association Oct. 4, 1927, deviates from the above on the Vie, hA, and 3A inch sizes as follows: 9A 6-inch size, nominal thickness =

Vi inch, maximum thickness =0.520 inch; 5s-inch size, width across flats, maximum = 1.0000 inch, minimum

=0.969 inch; K-inch size, width across flats, maximum = 1.1875 inch, minimum = 1.150 inch.
AMERICAN NATIONAL BOLT AND NUT PROPORTIONS 143

Table 70.Dimensions of finished square and hexagon regular nuts

Sizes

Width across flats Minimum width

across corners Thickness

Maxi- mum

Mini- mum Hexagon Square Nominal Maxi- mum

Mini- mum

Inches

0. 4375 .5625

.6250

.7500 .8125

.8750

.9375

1. 1250

1. 3125

1.5000

1. 6875

1. 8750

2. 2500

2. 6250 3.0000

3. 3750

3. 7500

4. 1250

4. 5000

Inches

0. 428 .552

.613 .737

.799

.861 .922

1. 108

1. 293 1.479

1.665

1. 850

2. 222

2. 593 2.964

3. 335

3. 707

4. 078

4. 449

Inches

0.488

.629 !840

.911

1. 051 1.263

1.474

1.686

1. 898

2. 109

2. 533

2. 956

3. 379 3.802

4. 226

4. 649 5.072

Inches

0. 588 .758

.842

1. 012

1.097

1. 182

1. 266

1. 521 1.775

2.031 2.286

2.540

3.051

3. 560

4. 070

4.579 5.090

5. 599 6.108

Inches

7/16

35/64 2^2 4%4%

1me

1*%2

1 3 ^2

2Mb 2%

2%

Inches

0. 225 .273

.336

,495 .559

.670

,781

1.019

1.115

1. 338

1. 560

1.783

2. 005

2. 228

2. 450

2. 673

Inches

0.212

.258 .320

.473

.535 .642

.750

.858

1.072

1. 288

1. 503

1.718

I
144 NATIONAL SCREW THREAD COMMISSION

Table 71.

Dimensions of castellated nuts

D A B T H j

Sizes

Width across flats Mini- mum

width

across corners

Over-all thickness Thickness, nominal

Slot

Maxi- mumMini- mum Nominal Maxi- mumMini- mum Width Depth

1 2 3 4 5 6 7 8 9 10 H

Me

*i 6 YlMe-- - %

U%

1.m1H

1H

Inches

0. 4375 .5000

.5625 .6250

.7500 .8750

.9375

1. 1250

1. 3125

1.5000

1. 6875

1.8750

2. 2500

Inches

0.428

.489

.551 .612

.737 .860

.922

1. 108 1.293

1.479

1.665 1.850 2.222

Inches

0. 488

.557 .628

.699 .840 .980

1. 051 1.263 1.474

1.686

1.898

2. 109

2. 533

Inches

2%4Me

2^2

*Me 2%2

IJ.; 1 ! 1%2 IK

Inches

0.288

.335 .414

.462 .573 .620

.731 .826

.921

1. 017

1. 173 1.272 L 525

Inches

0.275

.321 .398 .444

.553

.598

.707

.799

.891 .983

1. 139 1.229

1.475

InchesMe%

2%4Me

2^2

2%2

*Me m

InchH*H

%2H2

%2

5A2%2

%2%3H

Inch%2Me

MeH

H

H

H

M«

Me%
AMERICAN NATIONAL BOLT AND NUT PROPORTIONS 145

Table 72.Dimensions of finished and semifinished jam nuts 01

30' V

^7

<oiDO

8Lb

3T

Tl

A B 41

Width across flats

Maxi- mumMini- mum

Width

across corners of mini- mum

Thickness Nominal Maxi- mum

Mini- mum

Inches

0. 4375 .5625

.6250

.7500

.8125 .8750

.9375

1. 1250

1. 3125

1.5000

1. 6875

1. 8750

2.2500

2. 6250 3.0000

3. 3750

3. 7500

4. 1250 4.5000

Inches

0. 428

.552

.613

.737 .799

.861 .922

1. 108

1. 293 1.479 1.665

1. 850 2.222

2.593

2. 964

3. 335

3. 707

4. 078

4.449

Inches

0.48S

840

911

1.051 1.263

1. 474

1. 686

1.898

2. 109

2. 533

2. 956

3. 379 3.802

4. 226

4. 649 5.072

Inches%2Me

1^2

7A

lm

mm

Inches

0. 163 .195

.227

.259 .323 .355

.387

.451 .516 .580

.644

.771 .900

1.029

1. 158

1.286 1.540

1. 669

1. 798

Inches

0. 150 .180

.211

.241 .303

.333

.363 .424

.484

.545

.606

.729

.850

.971

1. 093

1. 214

1. 460

1.581

1. 703 Table 73.

Dimensions of hexagon light nuts

D A B H

Sizes Width across flats

Mini- mum

width

across corners

Thickness

Maxi- mumMini- mum Hexagon Nominal Maxi- mum

Mini- mum

2 3 4 5 6 7 Inch

0. 4375 .5000

.5625 .6250

.7500

Inch

0.428

.489

.551 .612 .737

Inch

0.488

.557 .628 !840

Inch%2

21/64 He

Inch

0. 225 .273 .336 .384

.448

Inch

0.212

.259

.320 .366

.428

Mo- H-

^6--
146 NATIONAL SCREW THREAD COMMISSION

Table 74.Dimensions of hexagon and square machine screw nuts and square

stove bolt nuts

-H7

B

i

Width across flats Width

across corners of hexagon

Thickness

Maxi- mum

No. 0—0.0600... No. 1—0.0730... No. 2—0.0860... No. 3—0.0990... No. 4—0.1120... No. 5i—0.1250.. No. 6—0.1380... No. 8 1—0.1640. No. 10 1—0.1900 No. 12 1—0.2160 % 1—0.2500...;. Me 1—0.3125.... % i—O.3750 Me—0.4375 0.5000

Inch

0. 1562 .1562

.1875

.1875

.2500

.3125

.3125

.3437

.3750

.4375 .4375

.5625 .6250

.7500

.8125

Mini- mumMini- mumNominal

Inch

0.150

.150

.180 .180

.241 .302

.302 .332

.362

.423

.423

.545 .607

.729

.790

Inch

0. 171 .171 .205

.205 .275

.344

.344 .378

.413 .482

.482

.621 .692

.831

.901

InchHi

He

MeHi

7Ai

5 32 %2H

^32

Maxi- mum

Inch

0.050

.050

.066

.114

.114

.130

.130

.161 .193

.225

.257

.321

Mini- mum

Inch

0.0.043

.057

.057 .087 .102

.102

.117

.117 .148

.178

.208

.239

.269 .299

i These sizes in the coarse-thread series are interchangeable with the following sizes of American National standard stove-bolt nuts: Machine screw Stove

bolt

No. 5 InchX

%2Me

%2H

Me

3A

No. 8 No. 10 No. 12 K-inch M6-inch ^6-inch..
AMERICAN NATIONAL BOLT AND NUT PROPORTIONS 147

Table 75.

Dimensions of finished hexagon cap screw heads

lie

,

1 — i-rt

30°-

. JL 64

D A B H

Sizes Width across flats Width

across corners Height

Maxi- mumMini- mumMini- mumNominal Maxi- mum

Mini- mum

1 2 3 4 5 6 7 U ' Inches

0. 4375 .5000

.5625 .6250 .7500

.8125 .8750

1.0000

1. 1250

1. 3125

1. 5000

i. 6875

Inches

0. 428

.489

.551 .612

.737 .798

.860

.983

1. 106

1. 292

1. 477

1. 663

Inches

0. 488

.557 .628

.698 .840

.910 .980

1. 121 1.261

1. 473

1. 684

1. 896

InchHe mi

%2%2 %4 %

%

15/16

Inch

0. 194 .242

.289 .337

.385

.433

.481 .576 .672

.768

.863 .959

IncW

0.181 .227

.273

.319

.365

.411 .457 .549

.641 .733

.824 .916

hM1

VlO I

°Ao

5A% —- 1m

m

Note.—Cap screws with hexagon heads are similar to machine bolts with hexagon heads, Table 68, and

they may be used interchangeably.
148 NATIONAL SCEEW THREAD COMMISSION

Table 76.

Open-end wrench openings

Basic width

across flats, bolt heads and nuts

Clear- anceToler- ance

Dimensions of measuring blocks

for wrench

openings Maxi- mum

Mini- mum

1 2 3 4 5

Inches Inch Inch inches T ft inches %2 —0. 1562 0.0014 0.005 0. 163 0.158

3/i6—0. 1875 .0016 .005 .194 .189 14—O. 2500 . 0018 . 005 . 257 252 M6—0. 3125 . 0019 .007 321 314

1 ^2—0. 3437 . 0022 . 007 353 . 346 H—0. 3750 .0024 .007 .384 .377 Vi6—0. 4375 .0025 .007 .447 .440 V2—0. 5000 . 0030 .007 . OIU . ouo

•He—0. 5625 . 0035 . 007 .0/0 . OOD

5/i—0. 6250 '. 0040 '. 007 . OoO . ozy H—0.7500 .0050 .008 .763 .755 *iH6—0.8125 .0050 .008 cor . OZO . 810 —0. 8750 . 0050 . 008 QQQ . 000 . OoU —0. 93"/

5

.' 0055 '. 009 . yOiS 943 1—1. 0000 '. 0060 . 009 1. 015 L006

lj^—1. 1250 .0070 .010 1. 142 1. 132

1. 2500 . 0070 . 010 1. 267 1. 257 l^—j^ 3125

° 0075 '. Oil 1. 331 1. 320 \Yi-i 5000 ' 0090 . 012 1. 521 1.509

li Ho—1. 6875 !0095 !013 1.710 1.697 1^—1. 8750 .0100 .013 1. 898 1.885 2*4—2. 2500 .0120 .015 2. 277 2. 262 2S4—2. 6250 .0140 .017 2. 656 2. 639 3—3. 0000 .0160 .019 3.035 3. 016 3^—3. 3750 .0180 .021 3. 414 3. 393 3M—3. 7500 .0200 .023 3. 793 3. 770 4*6—4. 1250 .0220 .024 4.171 4. 147 4^—4. 5000 .0230 .026 4.549 4.523

Section VIII B. Standards for Proportions of Threaded Products

Indorsed by the Commission 22

1. REFERENCES

The commission further indorses the standards for proportions of the following threaded products as listed in the references below:

1. Round unslotted-head bolts.

(a) Square-neck carriage bolts

(6) Fin-neck carriage bolts

(c) Ribbed carriage bolts

(d) Step bolts

(e) Button-head machine bolts

(J) Countersunk carriage bolts 1 Set screws

(a) Headed set screws

(6) Headless slotted set screws Tap rivets Plow bolts

Reference

- 1,2

- 1,2

- 1,2

- 1,2

- 1,2

1, 2

2

111

163 M See also Appendix 6, p. 241.
AMERICAN NATIONAL ACME SCREW THREADS 149

1. " United States Government Master Specification for Bolts,

Nuts, and Screws," Federal Specifications Board specification No.

548, promulgated March 5, 1928.23 Issued in mimeographed form

by the Federal Specifications Board, Bureau of Standards,

Washington, D. C.

2. "Tentative American Standard Round Unslotted Head Bolts

Carriage, Step, and Machine Bolts." Report No. B 18e-1927,

issued and sold by the American Standards Association, 29 West

Thirty-ninth Street, New York, N. Y. Price 35 cents.

3. "Plow Bolts." United States Department of Commerce

Simplified Practice Recommendation No. 23, February 19, 1924.

Issued by the Bureau of Standards and sold by the Superintendent

of Documents, Government Printing Office, Washington, D. C.

Price 5 cents. Also published as Report No. B 18f—1928, "Tentative American Standard for Plow Bolts." Issued and sold by

the American Standards Association, 29 West Thirty-ninth Street,

New York, N. Y. Price 35 cents. SECTION IX. AMERICAN NATIONAL ACME SCREW THREADS

(STANDARD PRACTICE)

1. GENERAL AND HISTORICAL

When formulated, prior to 1895, Acme screw threads were intended

to replace square threads and a variety of threads of other forms used

chiefly for the purpose of producing traversing motions on machines,

tools, etc. Acme screw threads are now extensively used for a variety

of purposes. For ordinary use, where lateral looseness is not objectionable, clearances between the screw and nut are provided at the

major and minor diameters and on the sides of the thread. These

allow free movement of the screw in the nut without appreciable

longitudinal looseness or end play. This quality of fit is provided for in class 1 herein.

There are cases in which lateral tightness is desirable, as, for example

where the nut acts as the support of a long screw which otherwise

would sag or spring out of position, or where the screw operates in a

vertical or inclined position, or on precision lead screws. In classes

2, 3, and 4 herein, the Acme thread is modified to have a bearing on

the minor diameter and such modification is recommended for accurate lead screws of any appreciable length, and for other adjusting screws where excessive side play is objectionable, as on valve stems. For such applications the so-called square thread, actually a thread

having an included angle of 3° to 10°, because of the impracticability of producing a truly square thread, has continued in use to some extent

33 This specification also includes specifications for machine screws, cap screws, and stove bolts which are based on a tentative report of subcommittee No. 3 of the A. S. A. Sectional Committee on Bolt, Nut, and

Rivet Proportions, but not approved by that committee.
150 NATIONAL SCREW THREAD COMMISSION

because bearing on the top or bottom of the thread is readily obtained.

Also, the wearing surface of the square thread at the minor diameter

is somewhat greater than for an Acme thread of the same pitch, but

this is counterbalanced by longer wearing life of the Acme thread in the nut on the sides of the threads, and the greater strength of the

base section of the Acme thread, as well as the greater ease of pro- duction. The advantage may he with the square thread only when

minimum frictional resistance is an important factor, as, the line of thrust being parallel with the screw, the friction in a square thread is less than in a thread having sloping sides. It is believed, however,

that applications in which an Acme thread of corresponding dimensions would not function equally as well as a square thread would be

very exceptional. When the so-called square thread is considered

necessary, the specifications given herein for thread series, classifica- tion, and tolerances for Acme threads can be applied with equal facility to square threads.

2. TERMINOLOGY

The terms and symbols relating to screw threads, which are used

herein and not otherwise defined, are defined in Section II.

3. AMERICAN NATIONAL ACME FORM OF THREAD

(a) SPECIFICATIONS

1. Angle of Thread.—The angle between the sides of the thread

measured in an axial plane shall be 29°. The line bisecting this 29°

angle shall be perpendicular to the axis of the screw thread.

2. Depth of Thread.—The basic depth of the thread shall be equal

to one-half of the pitch.

3. Thickness of Thread.—The basic thickness of the thread at a diameter smaller by one-half the pitch than the basic major diameter

shall be equal to one-ha1! of the pitch.24 4. Clearance at Minor Diameter.—A clearance shall be provided

at the minor diameter for class 1 Acme by making the minor diameter

of the screw 0.020 4v smaller than basic, and for classes 2, 3, and 4

Acme by making the minor diameter 0.005 VP smaller than basic.

5. Clearance at Major Diameter.—A clearance shall be pro- vided at the major diameter for all classes by making the major diameter of the nut or threaded hole at least 0.020 inch larger than basic.

6. Fillets at Minor Diameter.—Fillets at the juncture of sides and root of the thread of the screw will develop on account of the round

ing of the corners of the threading tool and the side cutting action of milling cutters when these threads are milled. It will be necessary,

24 The diameter at which the thickness of thread is measured corresponds to the basic pitch diameter of

60° screw threads used for bolts, nuts, etc. On threads whose included angle is equal to 45° or more, the

thickness of the thread is controlled and measured by the pitch diameter. On threads whose included

angle is less than 45°, the thickness of the thread should be controlled directly.
AMERICAN NATIONAL ACME SCREW THREADS 151

therefore, on tapped holes for all classes of fits, to provide a fillet or bevel at the minor diameter of the tap to remove the corner of the

crest of the thread of the tapped hole. This fillet, or bevel, should be

at least 0.010 inch for pitches of 3 threads per inch and finer, and at

least 0.020 inch for pitches coarser than 3 threads per inch.

(b) ILLUSTRATION

* The basic form of this thread is shown in Figure 33. P

Fig. 33.American National Acme form of thread

NOTATION

^4=29° 00'. a =14° 3C p=pitch n=number of threads per inch N=number of turns per inch h=0.5p, basic depth of thread t=thickness of thread .F=0.37069p=basic width of flat

4. THREAD SERIES

As these threads are used for such a wide variety of purposes, it is not feasible arbitrarily to select and designate any given combinations

of diameters and pitches as standard. It is recommended, however,

that as far as practicable, some one of the pitches shown in Table 77

be used; also, that the diameter be not less than the minimum

diameter specified for each pitch. If a greater lead is required on a given diameter than that corresponding to the recommended maximum pitch, it is advisable to use a multiple thread of finer pitch rather

than a single thread of coarser pitch.
152 NATIONAL SCREW THREAD COMMISSION

Table 77.

Recommended pitches and corresponding minimum major diameters for American National Acme threads

Number of threads per inch, n Pitch, p

Basic depth of thread, h=0.5p

Recom- mended minimum

major

diameter 1

Basic width

of flat, .F=0.37069p

1 2 3 4 5

1 Inch1. 00000 .75000

.66667

.50000

.40000

. 33333 .25000 .20000

. 16667 .12500

.10000

. 08333

Inch

0.5000

.3750

.3333 .2500

.2000

.1667

.1250 .1000

.0833 .0625

.0500

.0417

Inches

4. 5000

3. 5000

3.0000

2. 2500

1. 7500

1. 5000

1. 1250 .8750

.7500

.5625

.4375 .3750

Inch

0. 3707

.2780

.2471 .1853

.1483

.1236 .0927

.0741 .0618

.0463

.0371 .0309

114 \y2 22H

3

4

56

810

12

i These recommended diameters correspond to a maximum helix angle (at the minor diameter) of approx- imately 5°. 5. CLASSIFICATION AND TOLERANCES

There are established herein for general use four distinct classes of

fit of American National Acme screw threads, the first two covering

adjusting or traversing screws, and the last two covering lead, screws on which it is usually necessary that the lead of the

thread be far more accurate than on adjusting screws. These four

classes, together with the accompanying specifications, are for the

purpose of insuring a uniform practice on screw-thread production

throughout the country. They are designated as follows:

Class 1. For general use. Class 2. Adjusting screws with limited side play.

Class 3. Commercial lead screws. Class 4. Precision lead screws. In designating the various classes of fit in these specifications the

class number is followed by the word "Acme" in order to distinguish

this classification from that applied to the various fits of fastening screws as given in Section III.

(a) GENERAL SPECIFICATIONS The following general specifications apply to all classes of fit specified for Acme screw threads

:

1. Uniform Minimum Nut.—The minor diameter and the thick- ness of thread in the minimum threaded hole or nut correspond to the

basic size, while the minimum major diameter gives the basic clearance,

the tolerances on diameters being applied above the basic size. 2. Tolerances.—(a) The tolerances specified represent the ex- treme variations allowed on the product.
FITS FOR ACME THREADS 153

(b) The tolerances on diameters of the nuts or threaded holes are

plus, and are applied from the minimum nut sizes to above the minimum nut sizes.

(c) The tolerances on diameters of the screws are minus, and are applied from the maximum screw sizes to below the maximum screw

sizes. (d) The tolerances on the thicknesses of threads are minus, and

s are applied from the maximum thread thickness to below the maximum thread thickness.

(e) The thread thickness tolerances for a screw and nut of the same diameter, pitch,' and class of fit are equal.

(f) The thread thickness tolerances include lead and angle errors. On classes 3 Acme and 4 Acme, the maximum permissible lead variations are specified.

(g) The thread thickness tolerances are obtained by adding together

three values, or increments, one dependent upon the basic major

diameter, another upon the length of engagement, and the third

upon the pitch of the thread.

(7i) The tolerances on the major diameters of the screws and minor

diameters of the nuts are based upon the pitch of the thread.

(i) The maximum major diameter of a screw is the basic diameter.

(j) The minimum major diameter of the nut is at least 0.020 inch

larger than the basic major diameter.

(fc) The maximum major diameter of the nut of a given pitch is such as to result in a flat equal to 0.3707^ — 0.0052 inch when the

pitch diameter of the nut is at its maximum value. When the minimum nut is basic, its maximum major diameter will be above the

basic major diameter by the amount of the specified pitch diameter

tolerance plus 0.02 inch.

(Z) The minimum minor diameter of a screw of a given pitch is such as to result in a flat at the root equal to 0.3707p when the pitch

diameter of the screw is at its minimum value.

(b) CLASSIFICATION OF FITS

1. Class 1 Acme.—(a) Definition.—This class is intended to cover

the manufacture of threaded adjusting screws for general purposes

where a considerable amount of shake or play, both side play and end

play, is not objectionable.

This class is made with large allowances to permit ready assembly

even when the threads are rough or dirty.

(b) Allowances.—An allowance is provided at the minor diameter

which is obtained by making the maximum minor diameter of the screw 0.020y5> smaller than the basic minor diameter. Also, there

is an allowance between the sides of the thread on the screw and nut
154 NATIONAL SCEEW THREAD COMMISSION

obtained by making* the thickness of the thread on the screw 0.005 -Jp

less than the basic thread thickness.25 (See fig. 34.)

M/N. 7V//C/W<f.5S OF" MAX.

t/y/?£:a o on screw

SCREW

Fig. 34.

Illustration of allowances, tolerances, and crest clearances^

class 1 Acme

NOTATION p=pitch

h =basic thread depth Heavy line shows basic size.

(c) Tolerances.—The tolerance on the thickness of the thread in

both screw and nut is obtained by adding three values, or increments,

as follows:

Diameter increment =0. OOIOV-D Length of engagement increment. = .0010 Q

Pitch increment = . 0050Vp

where

D=basic major diameter in inches Q=length of engagement in inches p—pitch of thread in inches

25 Both allowances are obtained when cutting a screw by setting the threading tool having a flat of basic width to cut a thread depth 0.010 Vpdeeper than basic.
FITS FOR ACME THREADS 155

(d) Allowance and tolerance values.—Tables 78 and 79 give the

allowances and tolerances for major and minor diameters. They

also give tolerance increments for thread thickness based upon the

above formulas. Inasmuch as the diameter corresponding to a given pitch will ordinarily have a value not less than the recom- mended minimum given in column 4, Table 77, and not greater

than three times that value, the diameter increment for all diameters

corresponding to a given pitch may be taken as the mean of the

increments obtained for the above limiting values without appreciably

note: dottbp t-th/e .shows basic sfz.e~

Fig. 35.

Illustration of loosest condition for class 1 Acme, 4 threads per

inch, S}4, inches diameter, 6 inches length of engagement

affecting the value of the thread thickness tolerance obtained by

adding the respective increments. Thus, in column 4, Table 78,

the diameter and pitch increments are combined according to the

following formula:

Column4, Table 78 = .0050 V? +

aQQ1Q fl + V?) ^coiumn 4> Table 77

The total thread thickness tolerance is obtained by adding together

the increments obtained from column 4, Table 78, and column 2, Table 79. The resulting tightest and loosest conditions of fit are

illustrated in Figures 35 and 36. 18415°—29 11
156 NATIONAL SCREW THREAD COMMISSION

(e) Example.—Three and one-fourth inches diameter, 4 threads

per inch, 6 inches length of engagement, class 1 Acme

:

From Table 78 we get for the screw: Maximum major diameter =3. 2500

Minimum major diameter = 3. 2500 —0. 0125=3. 2375

Maximum minor diameter = 3. 2500— . 2600=2. 9900

Maximum thickness of thread = . 1225 And for the nut: Minimum major diameter = 3. 2500+0. 0200=3. 2700

Minimum minor diameter = 3. 2500— . 2500=3. 0000

Maximum minor diameter = 3. 0000+ . 0125=3. 0125

Maximum thickness of thread = . 1250 And for the thread thickness tolerance: From Table 78, pitch and diameter increments = . 0039 From Table 79, engagement increment (6 inches) = . 00601 Total = . 00995

Fig. 36.

Illustration of tightest condition for class 1 Acme, 4- threads per inch, 3}/i inches diameter Increment values are given to five decimal places for purposes o: calculation. The final result should be rounded off to the nearest

third decimal place. The thread thickness tolerance for both screw and nut in this example would be, therefore, 0.010 inch.
FITS FOR ACME THREADS 157

Table 78.

Class 1 Acme, allowances, thread proportions, and pitch and diameter

increments

Number of threads per inch Pitch

Allow

ance on

thread

thick- ness

Combined

pitch and di- ameter

incre- ments of thread

thick- ness tol- erance

Screw Nut

_

1 oler- ance on

major

diameters, minus

Maxi- mum

minor

diameter =

basic major

diameter minus

Maxi- mum

thread

thick- ness

Toler- ance on

minor

diameter, plus

Mini- mum

minor

diameter =

basic major

diameter minus

Maxi- mum

thread

thick- ness

Mini- mum ! major

diameter =

basic major

diameter plus

1 s

9

o 5 6 7 8» 9 10 11

Inch Inch Inch Inch Inches Inch Inch Inch Inch Inch

1 1. 00000 0. 0050 0. 00790 0. 0500 1. 0200 0. 4950 0. 0500 1. 0000 0. 5000 0. 0200 IM— . 75000 . 0043 . 00689 .0375 .7673 .3707 .0375 .7500 . 3750 .0200 1H . 66667 .0041 .00645 .0333 .6830 .3293 .0333 .6667 .3333 .0200

2 . 50000 . 0035 .00559 .0250 .5141 .2465 .0250 .5000 .2500 .0200 2^ .40000 .0032 .00497 .0200 .4126 .1968 .0200 .4000 .2000 .0200

3 . 33333 .0029 . 00456 .0167 .3449 .1638 .0167 .3333 .1667 .0200

4 . 25000 .0025 .00395 .0125 .2600 .1225 .0125 .2500 .1250 .0200

5 .20000 .0022 . 00351 .0100 .2089 .0978 .0100 .2000 .1000 .0200

6 . 16667 .0020 .00322 .0083 .1748 .0813 .0083 .1667 .0833 , .0200 8 . 12500 .0018 .00279 .0063 .1321 .0607 .0063 .1250 .0625 .0200

10 . 10000 .0016 . 00248 .0050 .1063 .0484 .0050 . 1000 .0500 .0200

12 . 08333 .0014 .00228 .0042 .0891 .0402 .0042 .0833 .0417 .0200 Table 79.

Class 1 Acme, length of engagement increments of thread thickness

tolerances

Length Length of Length Length of

of en- engage- of en- engagegage- ment in- gage- ment in- ment crement ment crement

1 1 %

Inches Inch Inches Inch

0. 250 0. 00025

. 00038 4.000 0. 00400 .375 4. 500 . 00450 .500 .00050 5.000 . 00500

.625 .00063 5. 500 . 00550 .750 . 00075 6.000 . 00600

1.000 .00100 6. 500 . 00650

1. 250 .00125 7. 000 .00700

1. 500 . 00150 7. 500 . 00750

1. 750 .00175 8. 000 .00800

2. 000 .00200 9. 000 . 00900

2. 500 .00250 10. 000 . 01000

3. 000 . 00300 11. 000 . 01100

3. 500 . 00350 12. 000 . 01200

2. Class 2 Acme.—(a) Definition.—This class is intended to cover the manufacture of threaded adjusting screws for general

purposes, where the amount of side play must be kept to a minimum,

such as valve stems, etc. This class is made with allowances to permit ready assembly and

lubrication.

(b) Allowances.—A small allowance is provided at the minor diameter which is obtained by making the maximum minor diameter of
158 NATIONAL SCREW THREAD COMMISSION

the screw 0.005ViP smaller than the basic minor diameter. Also

there is an allowance between the sides of the thread on the screw and nut obtained by making the thickness of the thread on the screw

0.00125 4v less than tne Dasic thread thickness.26 (See fig. 37.)

MAX.. THfCKNFSS 0/=* THREAD /N NUT

BASSO THICKNESS

OF* TM&EJkO

Mf/SL T/i/CKNESS OF

StfM TH/CKNESS Qfj THREAD OH^CREW

MAX. Tfi/CKNESS OF

JN NUT

SCREW

THREAD ON SCRE W

Fig. 37.

Illustration of allowances, tolerances, and crest clearances

classes 2, 3, and 4 Acme

NOTATION p=pitch

ft —basic thread depth Heavy line shows basic size

(c) Tolerances.—The tolerance on the thickness of the thread in both screw and nut is obtained by adding three values, or incre

ments, as follows:

Diameter increment = 0.0010V-D Length of engagement increment = .0005 Q_

Pitch increment = .0050Vp

where

D=basic major diameter in inches Q=length of engagement in inches p=pitch of thread in inches

» Both allowances are obtained when cutting a screw by setting the threading tool having a flat of basic width to cut a thread depth 0.0025 Vp deeper than basic.
FITS FOR ACME THREADS 159

(d) Allowance and tolerance values.—Tables 80 and 81 give the

allowances and tolerances for major and minor diameters. They

also give tolerance increments for thread thickness based upon the

above formulas. Inasmuch as the diameter corresponding to a given pitch will ordinarily have a value not less than the recommended

minimum given in column 4, Table 77, and not greater than three I times that value, the diameter increment for all diameters corre- sponding to a given pitch may be taken as the mean of the increments obtained for the above limiting values without appreciably

Note.—Dotted line shows basic size.

Fig. 38.

Illustration of loosest condition for classes 2, 3, and 4- Acme, 4

threads per inch, 3)4, inches diameter, 6 inches length of engagement

affecting the value of the thread thickness tolerance obtained by

adding the respective increments. Thus, in column 4, Table 80,

the diameter and pitch increments are combined according to the

following formula:

Column 4, Table 80 = 0.0050Vff +

0<QQ1Q £+ ^3) Vcolumn 4, Table 77

The total thread thickness tolerances are obtained by adding together

the increments obtained from column 4, Table 80, and column 2,

Table 81. The resulting tightest and loosest conditions of fit are

illustrated in Figures 38 and 39.
160 NATIONAL SCREW THREAD COMMISSION

(e) Example.—%-inch diameter, 6 threads per inch, 2 inches

length of engagement, class 2 Acme:

From Table 80 we get for the screw: Maximum major diameter =0.7500 Minimum major diameter =0.7500— 0.0083= .7417 Maximum minor diameter = .7500— .1687= .5813 Minimum minor diameter = .5812— .0041= .5771 Maximum thickness of thread = .0828 And for the nut: Minimum major diameter =0.7500 + 0.0200= .7700 Minimum minor diameter = .7500— .1667= .6833 Maximum minor diameter = .6833+ .0041= .6874 Maximum thickness of thread = .0833 And for the thread thickness tolerance: From Table 80, pitch and diameter increments = .00322 From Table 81, engagement increment = .00100 Total = .00422

Fig. 39.Illustration of tightest condition for classes 2, 8, and 4 Acme, 4

threads per inch, 8\i, inches diameter Increment values are given to five decimal places for purposes of calculation. The final result should be rounded off to the nearest

third decimal place. The thread thickness tolerance for both screw and nut in this example would be, therefore, 0.004 inch.
FITS FOR ACME THREADS 161

Table 80.

Classes 2, 3, and 4 Acme, allowances, thread proportions, and pitch and

diameter increments

Number

of threads per inch Pitch

Allowance on

thread

thick- ness

Combined

pitch and

diameter

incre- ments

of thread

thick- ness

toler- ance

Radius

of

fillet at minor

diameter, screw and

nut

Screw Nut

Toler- ance on

major

diam- minus

M!axi- mum

minor

, a basic major

diam- minus

Toler- ance on

minor

diam- minus

Maxi- mum

thread

thickToler- ance on minor

diamplus

Mini- mum

minor

}a _

basic major

diamTT) 1 nil C ill J.-U.U.O

Maxi- mum

thread

thick- ness

Mini- mum

major

diambasic major

diameter

1 2 3 i 5 6 7 8 9 10 11 12 13

Inch Inch Inch Inch Inches Inch Inch Inch Inch Inch Inch

1 1. 00000 0. 0013 0. 00790 0. 02 0. 0500 L 0050 0. 0100 0. 4987 0. 0100 1.0000 0. 5000 0. 0200

Vyi .75000 .0011 . 00689 .02 .0375 .7543 .0087 .3739 .0087 .7500 .3750 .0200

\Vl . 66667 .0010 .00645 .02 .0333 .6708 .0082 .3323 .0082 .6667 .3333 .0200

2 - .50000 .0009 .00559 .02 .0250 .5035 .0071 .2491 .0071 .5000 .2500 .0200 2Y2 .40000 .0008 .00497 .02 .0200 .4032 .0063 .1992 .0063 .4000 .2000 .0200

3 . 33333 .0007 .00456 .01 .0167 .3362 .0058 .1660 .0058 .3333 .1667 .0200

4 . 25000 .0006 .00395 .01 .0125 .2525 .0050 .1244 .0050 .2500 .1250 .0200

5 .20000 .0006 .00351 .01 .0100 .2022 .0045 .0994 .0045 .2000 .1000 .0200

6 . 16667 .0005 . 00322 .01 .0083 .1687 .0041 .0828 .0041 .1667 .0833 .0200

8 . 12500 .0004 . 00279 .01 .0063 .1268 .0035 .0621 .0035 .1250 .0625 .0200

10 .10000 .0004 .00248 .01 .0050 .1016 .0032 .0496 .0032 .1000 .0500 .0200

12 .08333 .0004 .00228 .01 .0042 .0848 .0029 .0413 .0029 .0833 .0417 .0200 Table 81.

Classes 2, 8, and J+ Acme, length of engagement increments of thread

thickness tolerances

Length

of engage- ment

Length of engage- ment in- crementLength

of engage- ment

Length of engage- ment in- crement

1 2 1 2

Inches

0. 250

.375 .500

.625 .750

Inch

0. 00013

.00019

.00025

.00031 .00038

Inches

4.500

5.000

5. 500 6.000

6.500

Inch

0. 00225

.00250

.00275 .00300

. 00325 1.000

1.250

1. 500 1.750 2.000

.00050

.00063 .00075

.00088 .00100

7.000

7. 500 8.000

9.000

10. 000

.00350

.00375 .00400

. 00450

. 00500 2.500

3.000

3. 500 4.000

.00125

. 00150

. 00175 .00200

11.000 12.000. 005500

. 006000

3. Class 3 Acme (Commercial Lead Screw).—(a) Definition.—

This class is intended to cover the manufacture of threaded lead screws used on machine tools, etc. This class is made with allowances to permit ready assembly and

lubrication.

(b) Allowances.—The allowances for this class are the same as

for class 2 Acme, as given in Table 80.
162 NATIONAL SCREW THREAD COMMISSION

(c) Tolerances.—The tolerances are also the same as for class 2

Acme as given in Tables 80 and 81, with the addition of a definite

tolerance on lead. The tolerance on lead is plus or minus 0.002

inch per 12 inches of length; this to be measured by the advance of a nut of approximately the same length as the one to be used. The

specified tolerance on lead applies to the whole or any part of the

distance of 12 inches.

(d) Example.—2)4 inches diameter, 5 threads per inch, 4 inches

length of engagement, class 3 Acme:

From Table 80, we get for the screw: Maximum major diameter =2. 2500 Minimum major diameter =2. 2500—0. 0100=2. 2400

Maximum minor diameter =2. 2500— . 2022 =2. 0478

Minimum minor diameter =2. 0478— . 0045 =2. 0432

Maximum thickness of thread = . 0994 And for the nut: Minimum major diameter =2. 2500+ . 0200=2. 2700

Minimum minor diameter =2. 2500— . 2000=2. 0500

Maximum minor diameter =2. 0500+ . 0045 =2. 0545

Maximum thickness of thread = . 1000 And for the thread thickness tolerance: From Table 80, pitch and diameter increments =. 00351

From Table 81, engagement increment =. 00200

Total =.00551

Increment values are given to five decimal places for purposes of

calculation. The final result should be rounded off to the nearest

third decimal place. The thread thickness tolerances for both

screw and nut in this example would be, therefore, 0.006 inch.

4. Class 4 Acme (Precision Lead Screw).—(a) Definition.—

This class is intended to cover the manufacture of precision threaded

lead screws used in machine tools for tool room use, etc. This class is made with allowances to permit ready assembly and

lubrication.

(b) Allowances.—The allowances for this class are the same as for Class 2 Acme, as given in Table 80.

(c) Tolerances.—The tolerances are also the same as for class 2

Acme, as given in Tables 80 and 81, with the addition of a definite

tolerance on lead. The tolerance on lead is plus or minus 0.0010

inch per 12 inches of length; this to be measured by the advance of a nut of approximately the same length as the one to be used. The

specified tolerance on lead applies to the whole or any part of the

distance of 12 inches.

id) Example.—1J4 inches diameter, 8 threads per inch, 2^ inches

length of engagement, class 4 Acme:
GAGES FOR ACME THREADS 163

From Table 80 we get for the screw: Maximum major diameter =1.2500

Minimum major diameter =1. 2500—0. 0063 = 1. 2437

Maximum minor diameter =1. 2500— . 1268=1. 1232 Minimum minor diameter =1. 1232— . 0035 = 1. 1197 Maximum thickness of thread = . 0621 And for the nut: Maximum major diameter =1.2500+ .0200 = 1.2700 Minimum minor diameter =1. 2500— . 1250=1. 1250 Maximum minor diameter =1. 1250+ . 0035 = 1. 1285 Maximum thickness of thread = . 0625 And for the thread thickness tolerance: From Table 80, pitch and diameter increments . = . 00279

From Table 81, engagement increment = . 00125

Total = .00404

Increment values are given to five decimal places for purposes of

calculation. The final result should be rounded off to the nearest

third decimal place. The thread thickness tolerance for both screw and nut in this example would be, therefore, 0.004 inch.

6. GAGES

The inspection of threaded product by means of gages and measuring tools is necessary to maintain the product within the limits

specified and to prevent the use of threading tools after they have worn beyond proper limits. With the application of suitable methods

of gaging and with reasonably good workmanship, uniform and known

thread sizes will result.

(a) FUNDAMENTALS

Both "go" and "not go" gages, representing the extreme product

limits, are necessary for the proper inspection of American National

Acme screw threads. This and other fundamentals of the subject of

gaging screw threads, which are stated for fastening screws in division

5 of Section III, are also applicable to Acme threads.

(b) SPECIFICATIONS FOR GAGES

1. Limiting Dimensions.—Tables 82, 83, and 84 given herein are

for the purpose of establishing definite limits for gages used in the

inspection of Acme threads, rather than for the purpose of specifying

the gages required for the various inspection operations. The

dimensions as given are in accordance with the principles: (a) That

the "go" gage should check simultaneously as many elements as

possible and a "not go" gage can effectively check but one element;

and (6), that permissible variations in the gages be within the extreme

product limits.

2. Tolerances on Lead.—The tolerances on lead given in Table

82 are specified as an allowable variation between any two threads not

farther apart than 12 inches.
164 NATIONAL SCREW THREAD COMMISSION

3. Tolerances on Angle of Thread.—The tolerances on angle of thread, as specified in Table 82 for the various pitches, are tolerances on one-half of the included angle. This insures that the bisector of

the included angle will be perpendicular to the axis of the thread

within proper limits. The equivalent deviation from the true thread

form caused by such irregularities as convex or concave sides of thread, or slight projections on the thread form, should not exceed the

tolerances permitted on angle of thread.

4. Fillets at Minor Diameter.—"Go" threaded plug gages for

nuts have fillets at the minor diameter, the radii of which are not less than 0.010 inch for pitches of three threads per inch and finer, and

not less than 0.020 inch for pitches coarser than three threads per inch.

Table 82.Tolerances for "go" and "not go" thread gages, American National

Acme threads

Threads

per inch

Tolerance on

thread thick- ness at basic pitch lineTolerance in lead Tolerance on half angle of threadTolerance on

major diameter

Tolerance on r

Class 1

ninor diameter

Classes 2, 3, and 4 From— To— Classes

1 and 2 Classes3 and 4 From— To— From— To— From— To1 2 3 4 5 6 7 8 9 10 11 12

11Hm2__. 2H

3.

4

56

8

10

12

Inch

0. 0000

.0000

.0000

.0000

.0000

.0000 .0000

.0000

.0000

.0000

.0000 .0000

Inch

0.0008

.0007

.0006

.0006

.0005

.0005 .0004

.0004

.0003

.0003 .0002

.0002

Inch ±

0.0005

.0005 .0005

.0005

.0005

.0005

.0005

.0005

.0005

.0005

.0005 .0005

Inch ±

0. 0002

.0002

.0002 .0002

.0002

.0002

.0002

.0002 .0002

.0002 .0002

.0002

Deg. Min. ±

5

55

55

5

55

5

51010

Inch

0.0000

.0000

.0000 .0000

.0000

.0000

.0000

.0000 .0000

.0000 .0000

.0000

Inch

0. 0010

.0010

.0010

.0010 .0010

.0010 .0010

.0010

.0008

.0006

.0005 .0004

Inch

0. 0000

.0000

.0000

.0000

.0000

.0000

.0000 .0000

.0000 .0000

.0000 .0000

Inch

0. 0010

.0010

.0010

.0010

.0010

.0010 .0010

.0010

.0008 .0006

.0005 .0004

Inch

0.0000

.0000 .0000

.0000

.0000

.0000

.0000 .0000

.0000

.0000

.0000

.0000

Inch

0. 0010

.0009 .0008

.0007

.0006

.0006 .0005 .0005

.0004

.0004

.0003 .0003
GAGES FOR ACME THREADS

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NATIONAL SCREW THREAD COMMISSION

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OIL-WELL EQUIPMENT THREADS 167

SECTION X. MISCELLANEOUS SPECIAL THREADS

Section XA. Screw Threads for Oil-Well Drilling Equipment

The commission, through its subcommittee on oil-well casing

threads and the staff of the Bureau of Standards, has at various times

extended assistance to the American Petroleum Institute in those

parts of its program of standardization of oil-field equipment which

deal with specifications for screw threads and methods of gaging

screw threads.

The first problem in this field brought to the attention of the

commission was the great need for standardization of oil-well casing

threads. Definite work toward such standardization was initiated by

the Mid-Continent Oil and Gas Association in 1921, but this was

complicated by a proposal to simplify casing sizes and weights, and pro- vide new standard sizes of nesting casing required for the deeper well

drilling which is now necessary. Certain manufacturers had also endeavored to come to an agreement on thread standards. Through

the cooperative efforts of the American Petroleum Institute, the Standardization Committee of the Mid-Continent Oil and Gas Association,

and the commission, certain agreements as to diameters, pitches, and

tapers were effected. The complete standard for casing threads,

together with standards for drill pipe and tubing, are now published

as A. P. I. Standards No. 5-A, "Pipe Specifications," issued by the

division of standardization, American Petroleum Institute, 1508

Kirby Building, Dallas, Tex.

The commission indorses the screw thread and screw-thread gage

specifications included in the following American Petroleum Institute

standards

:

No. 3.-A. P. I. dimensional standards for cable drilling tool joints. No. 5-A. A. P. I. pipe specifications. No. 5-L. A. P. I. line pipe specifications. No. 7-B. A. P. I. specifications for rotary drilling taper joints. No. 11-A. A. P. I. specifications for cold-drawn and machined working barrels. No. 11-B. A. P. I. sucker rod specifications.

Section XB. American National Standard Hose Connections for

Welding and Cutting Torches

The specifications given herein, covering hose connections for welding and cutting torches, were finally approved and adopted by

the commission June 28, 1926. These specifications were formulated

and adopted in 1925, in essentially the same form, by the International Acetylene Association and the Gas Products Association, and

have been adopted by the National Board of Fire Underwriters and

various manufacturers.
168 NATIONAL SCREW THREAD COMMISSION

Dimensions essential to the interchangeability of parts have been

standardized. Other dimensions and details of design are optional, so that manufacturers may use their own judgment and follow then- usual practice as much as possible. Two sizes of connections are

specified, as illustrated in Figures 40 and 41.

HOSE A a C

, //VC// 1% -men 3 "*CH

76- /e

/8 J**±23^

Fig. 40.

"A" size of standard hose connections for welding and cutting torches

HOSE A c

u INCH INCH 375 ^?Sf

-t k . 31Z +-28S .eSo ±%£% .* —i t

187 ±°<&% Fig. 41.

"B" size of standard hose connections for welding and cutting torches

1. STANDARD DIMENSIONS

1. Screw threads corresponding to the American National fine thread series, and class 3, medium fit, are specified iD Figures 40 and

41, for which dimensions are given in Table 13. Right-hand threads are specified for oxygen and left-hand threads jorjuel gas.

2. Angle and outside diameter of internal seat.

3. Radius and distance of radius center of external seat from shank

shoulder.
WELDING-TORCH HOSE CONNECTIONS 169

4. Diameter of shank shoulder.

5. Diameter of hole in nut.

6. Small and large diameters of shank.

7. Diameter of hole through shank.

2. OPTIONAL FEATURES

1. Material.—Strength equal to or greater than that of free-

> turning high brass.

2. Diameter of hole through nipple.

3. Form of end of shank, except seating section as covered in "C"

Figures 40 and 41.

4. Length of shank.

5. Type and number of serrations on shank.

6. A second shoulder equal to the large diameter of the largest

shank to extend through the hole in the nut for appearance, to be

used or omitted for smaller diameter shanks.

7. Length and location of hexagon section on nut.

3. GAGES

Dimensions and designs of gages for maintaining the hose connection standards for welding and cutting torches are recommended

as follows: Note.—In connection with screw-thread gages see also Section III, division 5. Gage No.

1. "Go" and "not go" gage for depth of threaded recess and shank bore

A size hose connection, as shown in Figure 42. B size hose connection, as shown in Figure 47.

2. "Go" adjustable thread-ring gage for right-hand nipple thread

A size, K-24-NF-3

Minor diameter, maximum, 0.3299; minimum, 0.3294 inch. v Pitch diameter, maximum, 0.3477; minimum, 0.3474 inch. B size, %6-18-NF-3

Minor diameter, maximum, 0.5024; minimum, 0.5019 inch. Pitch diameter, maximum, 0.5262; minimum, 0.5259 inch.

3. "Go" adjustable thread-ring gage for left-hand nipple thread

A size, %-24 L. H.-NF-3

Minor diameter, maximum, 0.3299; minimum, 0.3294 inch. Pitch diameter, maximum, 0.3477; minimum, 0.3474 inch. B size, %6-18 L. H.-NF-3

Minor diameter, maximum, 0.5024; minimum, 0.5019 inch. Pitch diameter, maximum, 0.5262; minimum, 0.5259 inch.

4. "Not go" adjustable thread-ring gage for right-hand nipple thread—

A size, %-24-NF-3

Minor diameter, maximum, 0.3304; minimum, 0.3299 inch. Pitch diameter, maximum, 0.3458; minimum, 0.3455 inch. B size, %6-18-NF-3

Minor diameter, maximum, 0.5029; minimum, 0.5024 inch. Pitch diameter, maximum, 0.5237; minimum, 0.5234 inch.
170 NATIONAL SCREW THREAD COMMISSION

Gage No.

5. "Not go" adjustable thread-ring gage for left-hand nipple thread

A size, K-24 L. H.-NF-3

Minor diameter, maximum, 0.3304; minimum, 0.3299 inch. Pitch diameter, maximum, 0.3458; minimum, 0.3455 inch. B size, %<r-18 L. H.-NF-3

Minor diameter, maximum, 0.5029; minimum, 0.5024 inch. Pitch diameter, maximum, 0.5237; minimum, 0.5234 inch.

6. "Go" and "not go" double-end threaded setting-plug gage for Nos. 2 and 4

A size, %-24-NF-3

"Go" endMajor diameter, maximum, 0.3750; minimum, 0.3740 inch. Pitch diameter, maximum, 0.3477; minimum, 0.3474 inch. "Not go" endMajor diameter, maximum, 0.3689; minimum, 0.3684 inch. Pitch diameter, maximum, 0.3458; minimum, 0.3455 inch. B size, Ke-18-NF-3

"Go" endMajor diameter, maximum, 0.5625; minimum, 0.5620 inch. Pitch diameter, maximum, 0.5262; minimum, 0.5259 inch. "Not go" endMajor diameter, maximum, 0.5548; minimum, 0.5543 inch. Pitch diameter, maximum, 0.5237; minimum, 0.5234 inch.

7. "Go" and "not go" double-end threaded setting-plug gage for Nos. 3 and 5

A size, 3/8-24L. H.-NF-3

"Go" endMajor diameter, maximum, 0.3750; minimum, 0.3745 inch, Pitch diameter, maximum, 0.3477; minimum, 0.3474 inch. "Not go" end

Major diameter, maximum, 0.3689; minimum, 0.3684 inch. Pitch diameter, maximum, 0.3458; minimum, 0.3455 inch. B size, Me-18 L. H.-NF-3

"Go" endMajor diameter, maximum, 0.5625; minimum, 0.5620 inch. Pitch diameter, maximum, 0.5262; minimum, 0.5259 inch. "Not go" end

Major diameter, maximum, 0.554S; minimum, 0.5543 inch. Pitch diameter, maximum, 0.5237; minimum, 0.5234 inch.

8. "Go" and "not go" double-end thread plug gage for right-hand nut

thread

A size, %-24-NF-3

"Go" endMajor diameter, maximum, 0.3755; minimum, 0.3750 inch. Pitch diameter, maximum, 0.3484; minimum, 0.3481 inch. Gaging notch, 0.125 from back. "Not go" endMajor diameter, maximum, 0.3665; minimum, 0.3660 inch. Pitch diameter, maximum, 0.3503; minimum, 0.3500 inch. B size, %6-18-NF-3

"Go" endMajor diameter, maximum, 0.5630; minimum, 0.5625 inch. Pitch diameter, maximum, 0.5269; minimum, 0.5266 inch. Gaging notch, 0.125 from back. "Not go" end

Major diameter, maximum, 0.5510; minimum, 0.5505 inch. Pitch diameter, maximum, 0.5294; minimum, 0.5291 inch.
WELDING-TORCH HOSE CONNECTIONS 171

Gage No.

9. "Go" and "not go" double-end thread plug gage for left-hand nut thread

A size, %-24 L. H.-NF-3

"Go" endMajor diameter, maximum, 0.3755; minimum, 0.3750 inch. Pitch diameter, maximum, 0.3784; minimum, 0.3481 inch. Gaging notch, 0.125 from back. "Not go" endMajor diameter, maximum, 0.3665; minimum, 0.3660 inch. Pitch diameter, maximum, 0.3503; minimum, 0.3500 inch. B size, %6-lS L. H.-NF-3

"Go" endMajor diameter, maximum, 0.5630; minimum, 0.5625 inch. Pitch diameter, maximum, 0.5269; minimum, 0.5266 inch. Gaging notch, 0.125 from back. "Not go" end

Major diameter, maximum, 0.5510; minimum, 0.5505 inch. Pitch diameter, maximum, 0.5294; minimum, 0.5291 inch.

10. Taper gage for nipple seat

A size, as shown in Figure 43. B size, as shown in Figure 48.

11. "Go" ring gage for diameter of shank shoulder and concentricity of serrated portion

A size, as shown in Figure 44. B size, as shown in Figure 49.

12. "Not go" snap gage for shank shoulder diameter

A size, maximum, 0.3241; minimum, 0.3240 inch. B size, maximum, 0.4961; minimum, 0.4960 inch.

13. "Go" and "not go" snap gage for diameter of %-inch shank

B size

"Go" end, maximum, 0.4298; minimum, 0.4297 inch. "Not go" end, maximum, 0.4251; minimum, 0.4250 inch.

14. "Go" and "not go" snap gage for diameter of %6-inch shank

B size

"Go" end, maximum, 0.3748; minimum, 0.3747 inch. "Not go" end, maximum, 0.3701; minimum, 0.3700 inch.

15. "Go" and "not go" snap gage for diameter of 34-inch shank

B size

"Go" end, maximum, 0.3118; minimum, 0.3117 inch. "Not go" end, maximum, 0.3071; minimum, 0.3070 inch.

16. "Go" and "not go" snap gage for diameter of %6-inch shank

A size;

"Go" end, maximum, 0.2478; minimum, 0.2477 inch. "Not go" end, maximum, 0.2431; minimum, 0.2430 inch. B size

"Go" end, maximum, 0.2498; minimum, 0.2497 inch. "Not go" end, maximum, 0.2451; minimum, 0.2450 inch.

17. "Go" and "not go" snap gage for diameter of %-inch shank

A and B sizes

"Go" end, maximum, 0.1868; minimum, 0.1867 inch. "Not go" end, maximum, 0.1821; minimum, 0.1820 inch.

18. Master template for nose of shank

A size, as shown in Figure 45. B size, as shown in Figure 50.

19. Template gage for nose of shank

A size, as shown in Figure 46. B size, as shown in Figure 51. 18415°—29 12
NATIONAL SCREW THREAD COMMISSION

Fig. 42.—"(?o" and "not go" gage for depth of threaded recess, and shank bore, A size

Fig. 43.

Taper gage for nipple seat, A size

// // £

OI(M

Fig. 44.

"Go" ring gage for diameter of shank shoulder and concentricity of serrated portion, A size

J64

/2S" 5

^h.—

f

04O' T

Fig. 45.

Master template for nose of shank, A

size T

.040"—4pZ T Fig. 46.

Template gage for nose of shank, A size
WELDING-TORCH HOSE CONNECTIONS

4T

Fig. 47.

"Go" and "not go" gage for depth of threaded

recess, and shank bore, B size

Fig. 48.

Taper gage for nipple seat, B size

Fig. 49."Go" ring gage for diameter

of shank shoulder and concentricity

of serrated portion, B size

:I96R .05AI±

K—.035'

Fig. 50.

Master template for nose of shank, B size

.035' S3

T" j Fig. 51.

Template gage for nose of shank, B size
174 NATIONAL SCREW THREAD COMMISSION

Section XC. American National Rolled Threads for Screw Shells of Electric Sockets and Lamp Bases

The specifications given herein for American National rolled threads for screw shells of electric sockets and lamp bases, with the

exception of the recently adopted intermediate size, were published

in Bulletin No. 1474 of the American Society of Mechanical Engineers

entitled " Rolled Threads for Screw Shells of Electric Sockets and Lamp

Bases," which was a report of the A. S. M. E. Committee on Standardization of Special Threads for Fixtures and Fittings.

1. FORM OF THREAD

The thread form is composed of two circular segments tangent to each other and of equal radii, as showm in Figure 52. SOC/f£T SC/?EW SHELL

j3/}S£ SCKEW SHELL

s si 5 gin

till

Silg if

s C ¥ it ill! U«4 q UQ k * <* III

ill!

till

Fig. 52.

Illustration of allowance and tolerances, American

National rolled threads for screw shells of electric sockets and

lamp bases

2. THREAD SERIES

The sizes for which standard dimensions and tolerances have been

adopted are designated as follows: " Miniature, candelabra, intermediate, medium, and mogul."

The threads per inch, radii of thread form, and diameter limits for these sizes of lamp base screw shells, which are used on lamp bases,

fuse plugs, attachment plugs, and similar devices, are given in Table 85.
ELECTRIC SOCKET AND LAMP BASE THREADS 175

The corresponding dimensions and limits for socket screw shells,

which are used in electric sockets, receptacles, and similar devices, are given in Table 86.

3. GAGES

Gages are necessary to control dimensions in manufacture and to insure interchangeability and proper assembly.

(a) Gaging of Lamp Base Screw Shells.—(1) Working gages.—

For each size of lamp base screw shell there should be provided for control in manufacture, a "go" and a "not go" threaded ring gage

to govern the minor diameter and thread form, and "go" and "not

go" plain ring gages to govern major diameter.

(2) Inspection gages.—For purposes of inspection in the final acceptance of the product, a "go" threaded ring gage governing

minor diameter and thread form, and a "not go" plain ring gage

governing major diameter are sufficient.

(b) Gaging of Socket Screw Shells.—(1) Working gages.—For

each size of socket screw shell there should be provided, for control in

manufacture, a "go" and a "not go" thread plug gage to govern the

major diameter and thread form, and "go" and "not go" plain plug

gages to govern minor diameter.

(2) Inspection gages.—For the final acceptance of the product, a "go" threaded plug gage governing the major diameter and thread

form, and a "not go" plain plug governing minor diameter are

sufficient.

(c) Tolerances on Gages.—Manufacturing tolerances on inspection or working gages should not exceed 10 per cent of the tolerance on the product, and should be applied in such a direction that the

limiting dimensions of the screw shells which they are intended to gage are never exceeded.

Radii at the crest of the thread on gages should not exceed values

given in column 5, Tables 85 and 86, and should not be more than 10

per cent less than these radii; also, radii at the root of the thread on

gages should not be less than the values given in column 5 nor more

than 10 per cent greater.

Table 85.

American National rolled threads for lamp base screw shells

Size Threads

per inch Pitch Depth of thread Radius

Major diameter Minor diameter

Maxi- mum

Mini- mum

Maxi- mum

Mini- mum

2 3 4 5 6 7 8 9

Inch Inch Inches Inches Inches Inches Inches Miniature 14 0. 07143 0. 020 0. 0210 0. 375 0. 370 0. 335 0. 330 Candelabra. 10 . 10000 .025 .0312 .465 .460 .415 .410 Intermediate 9 . 11111 .027 .0353 .651 .645 .597 .591 Medium. 7 . 14286 .033 .0470 1.037 1.031 .971 .965 Mogul 4 .25000 .050 .0906 1. 555 1.545 1. 455 1. 445
176 NATIONAL SCREW THREAD COMMISSION

Table 86.

American National rolled threads for socket screw shells

Size Threads

per inch Pitch Depth of thread Radius

Major diameter Minor diameter

Maxi- Mini- Maxi- Mini- mum

1 2 3 1 5 6 7 8 9

Inch Inch Inch Inches Inches Inches Inches Miniature 14 0. 07143 0. 020 0. 0210 0. 3835 0. 3775 0. 3435 0. 3375 Candelabra 10 .10000 .025 .0312 .476 .470 .426 .420 Intermediate 9 .11111 .027 .0353 .664 .657 .610 .603 Medium 7 .14286 .033 .0470 1.053 1.045 .987 .979 Mogul 4 . 25000 .050 .0906 1. 577 1. 565 1. 477 1.465

Section XD. Screw Threads of Special Diameters, 12 Threads per

Inch (Including Railway Sizes)

Where special threads are required, it is sometimes essential to select a certain pitch as standard for a range of sizes. Also, in

general practice, where the pitch of a special thread is optional, the

uniform use of a selected pitch is advantageous. For such applications the 12 pitch is widely used, particularly for two distinct purposes as given below, but for different reasons.

Sizes of 12 pitch threads from one-half inch to and including 1%

inches are used in railroad practice, which require that worn stud

holes be retapped with a tap of the next larger size, the increment

being one-sixteenth inch throughout most of the range.

27 The 12-pitch threads are also widely used in machine construction,

as for thin nuts on shafts and sleeves. From the standpoints of good design and simplification of practice, it is desirable to maintain

shoulder diameters to one-eighth-inch steps. The 12 pitch is the

coarsest, for a thread of basic depth, which will permit a threaded

collar which screws onto a threaded shoulder to slip over a shaft, the

difference in diameter between shoulder and shaft being one-eighth

inch.

There are, therefore, presented herein, supplementary to Section

IV, " Screw threads of special diameters, pitches, and lengths of engagement," specifications and data covering a range of sizes of screw threads from one-half to 3 inches, inclusive, having 12 threads

per inch, and based on a length of engagement of 1 inch.

1. FORM OF THREAD

The American National form of thread profile as specified in Section III shall be used.

» See U. S. Department of Commerce Simplified Practice Recommendation No. 51, "Die Head Chasers."
AMERICAN NATIONAL 12-PITCH THREAD SERIES 177

2. THREAD SERIES

The nominal sizes and basic dimensions of the "American National

12-pitch thread series' ' are specified in Table 87.

3. CLASSIFICATION AND TOLERANCES

The general specifications and classification of fits given in Section

IV, herein, are applicable to the American National 12-pitch thread

series. The dimensions and tolerances for four classes of fit, based on a length of engagement of 1 inch, and derived from Tables 27 to

31, are given in Table 88. Table 87.

American National 12-pitch thread series

Identification Basic diameters

_ . JVietric equiv- Major Pitch Minor alent of Sizes Threads diameter diameter diameter major

per inch diameter D E K

1 2 3 4 5 6

Inches Inches Inches mm H— - 12 0.5000 0. 4459 0. 3917 12. 700 H«» 12 .5625 .5084 .4542 14. 288 % 12 .6250 .5709 .5167 15. 875

J M6 12 .6875 .6334 .5792 17. 463 % 12 .7500 .6417 19. 050 ma 12 .8125 .7584 .7042 20. 638 n 12 .8750 .8209 .7667 22. 225 !Me 12 .9375 .8834 .8292 23. 813

1 12 1. 0000 .9459 .8917 25. 400 lHe 12 1. 0625 1. 0084 .9542 26. 988 1H* 12 1. 1250 1. 0709 1. 0167 28. 575 IMe— 12 1. 1875 1. 1334 1. 0792 30. 163 1H 2 12 1. 2500 1. 1959 1. 1417 31. 750 iMc~- -- 12 1. 3125 1. 2584 1.2042 33. 338 m 12 1. 3750 1. 3209 1. 2667 34. 925 m 2 12 1. 5000 1. 4459 1. 3917 38. 100 w 12 1. 7500 1. 6959 1. 6417 44. 450 2 12 2. 0000 1. 9459 1. 8917 50. 800 2H 12 2. 2500 2. 1959 2. 1417 57. 150

2Vi 12 2. 5000 2. 4459 2. 3917 63. 500 2% 12 2. 7500 2. 6959 2. 6417 69. 850

3 12 3. 0000 2. 9459 2. 8917 76. 200

1 Standard size of the American National coarse-thread series.

1 Standard size of the American National fine-thread series,
178 NATIONAL SCREW THREAD COMMISSION
AMERICAN NATIONAL 12-PITCH THREAD SERIES

OOOS co^t<

OS rH CN) id t— t—

i

os o rH

01 CO 00 OS

r-l IN CN CO

rH TJH 00

lO rH lO O Tfl O O

CN 00

Ttl 00 88

>o 100

1 o oo

:S 8?

CN CO

CM CO O O

OS O OS O

CO lO

CN O CO o

1.

2584

1.

1.

2663

1.

.0079

.

1.

2640

1.

.0056

.

1.

2624

1.

.0040

.

1.

2604

1.

.0020

.

1.

1959 1.

2038

.0079 1.

2015

.0056 1.

1999

.0040 1.

1979

.0020

1.

1334 1.

1413

.0079 1.

1390

.0056 1.

1374

.0040 1.

1354

.0020

1.

0709 1.

0788

.

0079 1.

0765

.0056 1.

0749

.0040 1.

0729

.0020

1.

0084 1.

0163

.0079 1.

0140

.0056 1.

0124

.0040 1.

0104

.0020

.9459 .9538 .0079 .9515 .0056 .9499 .0040 .9479 .0020

.8834 .8913 .0079 .8890 .0056 .8874 .0040 .8854 .0020

.8209 .8288 .0079 .8265 .0056 .8249 .0040 .8229 .0020

.7584 .7663 .0079 .7640 .0056 .7624 .0040 .7604 .0020

.6959 .7038 .0079 .7015 .0056 .6999 .0040 .6979 .0020

.6334 .6413 .0079 .6390 .0056 .6374 .0040 .6354 .0020

.5709 .5788 .0079 .5765 .0056 .5749 .0040 .5729 .0020

.5084 .5163 .0079 .5140 .0056 .5124 .0040 .5104 .0020

.4459 .4538 .0079 .4515 .0056 .4499 .0040 .4479 .0020

S ' S_! £ o So So iSo §e §H

do 5

hSS 73 VH'

.2 5 Sft & cd a

w >h CD .•"S'S.S 5 s "Steal

TJ .s ^ .a .» -a
180 NATIONAL SCREW THREAD COMMISSION

4. GAGES

The specifications for gages given in Section IV are applicable.

Tolerances on diameter, lead, and angle for classes X, Y, and Z gages

are given in Table 89. Table 89.

Tolerances for thread gages, American National 12-pitch thread series

Class of gage

Tolerance on pitch diameter 1 Tolerance on lead 2 Tolerance on half angle of thread

Tolerance on major

or minor diameters i From— To— From— To-

» 3 I 5 6

Class X and all " not go "

Class Y

Class Z.

Inch

0.0000 .0002

.0004

Inch

0. 0003

.0006

.0011

Inch ±

0. 0003

.0003

.0004

Deg. Min. ±

10

10

10

Inch

0.0000

.0000 .0000

Inch

0. 0006

.0006

.0006

1 On "go" plugs the tolerance is plus, and on "go" rings the tolerance is minus. On "not go" plugs the

tolerance is minus, and on "not go" rings the tolerance is plus.

2 Allowable variation in lead between any 2 threads not farther apart than the length of engagement.
APPENDIX 1. DERIVATION OF TOLERANCES

1. PITCH DIAMETER TOLERANCES

(a) Tolerances for Fastening Screws.—The tolerances for fastening screws specified in Section III were arrived at by combining two factors, known

as the net pitch diameter tolerance and the gage tolerance. The theoretical net tolerances for all screws and nuts of a given class of fit bear a definite mathematical relationship to each other, and it was intended that these should in no way be reduced by permissible manufacturing tolerances for master gages; that is, gages within class X tolerances. Consequently the net tolerances were

increased by the equivalent diametrical space required to provide for the class X

tolerances on diameter, lead, and angle, to produce the extreme tolerances

specified for the product. In practice, the actual net tolerances will depend

upon the method of gaging and upon the accuracy of the gages used.

1. Basis of net tolerances. —The net pitch diameter tolerances for the various

classes of fit are based on the following series for a pitch of Ho inch:

Inch Class 1, loose fit 0. 0045

Class 2, free fit . 0030

Class 3, medium fit . 0020

Class 4, close fit . 0010

Pitch diameter tolerances for pitches finer than ^ inch are to each other and to the tolerance for y2 o inch as the 0.6th power of their respective pitches. Pitch diameter tolerances for pitches coarser than }io inch are to each other and to the tolerance for %o inch as the 0.9th power of their respective pitches.

The exponent 0.6 was chosen for pitches finer than % inch because the result- ing tolerances, except in two instances, do not vary more than 0.0001 inch from

the pitch diameter tolerances specified in the A. S. M. E. Machine Screw

Standard.

2. Gage tolerance.—The gage tolerance to be added to the net tolerance to obtain the extreme tolerance, which determines the absolute limits within which

all variations of the work must be kept, is determined as follows: Add together the following: Pitch diameter tolerance of "go" gage. Diametrical equivalent of lead tolerance of "go-" gage. Diametrical equivalent of angle tolerance of "go" gage. Pitch diameter tolerance of "not go" gage. Then subtract the following from the above sum:

One-half diametrical equivalent of lead tolerance of "not go" gage. Diametrical equivalent of angle tolerance of "not go" gage.

3. Tolerances for extension of American National fine-thread series.—For greater

consistency among the tolerances specified in Sections III and IV it was found

necessary to depart from the above basis for the extension of the American

National fine-thread series above l}/2 inches, and to specify tolerances obtained

by adding increments as given in Table 90 according to the method given below

under "(&)." 181
182 NATIONAL SCREW THREAD COMMISSION

All dimensions in iNCHts

I

\*

V 007-

Ji0O14 I

ooai o

.4

.oo/a ^

00//

Z//v£-/ Fig. 53.

Chart for determining tolerances for various classes of fit of special threads

Directions for Using Chart.—To determine the tolerance for a special screw or nut, given the diameter, threads per inch, and length of engagement: Lay a straightedge across lines Nos. 1 and 6, intersecting line

1 at the point corresponding to the diameter and line 6 at the point corresponding to the length of engage- ment, and note the point at which it intersects line 2. Then lay the straightedge across lines 2 and 7, intersecting line 2 at the point previously noted and line 7 at the point corresponding to the number of threads per inch. If the tolerance for a class 1 fit is desired, note the point of intersection of the straight- edge on line 5; a class 2 fit, on line 4; and a class 3 or 4 fit, on line 3. The scale readings on these lines give the tolerances, but to determine the tolerance for a class 4 fit divide the scale reading on line 3 by 2. The allowance for a class 1 fit is given opposite the threads per inch, line 7,
LEAD AND ANGLE EBEOES 183

(6) Tolerances for Screw Threads op Special Diameters, Pitches,

and Lengths of Engagement.—As stated in Section IV, the pitch diameter

tolerances for special sizes of threads of American National form as given in Tables 28, 29, 30, and 31 were obtained by adding three values, or increments, one dependent upon the basic major diameter, another upon the length of en- gagement, and the third upon the pitch, except that pitch diameter tolerances

listed in Section III were inserted in the tables in the positions corresponding to standard sizes, pitches, and lengths of engagement of the American

National coarse and fine thread series, and values above and to the left of these

inserted values were reduced where necessary so that none should exceed these standard values. Likewise values below and to the right of these inserted values were increased where necessary so that none should be less than these standard

values. The formulas from which the increments are derived are given in Table

90. Also tolerances corresponding to the sum of the increments may be obtained

directly from the chart, Figure 53. Table 90.

Schedule of tolerance increments for special threads

Class of fit Diameter

increment Length of engagement

increment

Pitch in- crement

1 3 3

Class 1, loose fit 0.002V# .002V5

.002V-D

.col VI)

0.002Q .002Q

.002Q

.001Q

0.020 Vp

.010 Vp

.005 Vp

.0025-Vp

Class 2, free fit Class 3, medium fit . . ....

Class 4, close fit ... . .__

2. RELATION OF LEAD AND ANGLE ERRORS TO PITCH DIAMETER

TOLERANCES

It has been stated in various sections of the report that the tolerances specified

for pitch diameter include all errors of pitch diameter, lead, and angle. Also, there were tabulated the errors in lead and angle, each of which could be compensated for by one-half of the specified pitch diameter tolerances. These

equivalents were derived from definite mathematical relations, which are given

below. A rigorous mathematical analysis upon which these formulas are based

is presented in Appendix 3 of Letter Circular No. 23, issued by the Bureau of Standards.

(a) Diameter Equivalent of Lead Error.—The formula expressing the

relation between lead error between any two threads within the length of engage- ment and its diameter equivalent is as follows: E' = (±p') cot a, in which

E' =pitch diameter increment due to lead error

p' —the maximum lead error between any two of the threads engaged

a =half angle of thread The quantity E

r is always added to the measured pitch diameter in the case of an external thread, and it is always subtracted in the case of an internal thread,

regardless of the sign introduced by the lead error p'

.

For threads of American National form, the above formula reduces to

£' = 1.7321 p'
184 NATIONAL SCREW THREAD COMMISSION

(6) Diameter Equivalent op Angle Error.—The general formula express- ing the relation between error in the half angle of thread and its diameter equivalent—that is, the amount of the pitch diameter tolerance absorbed by such an

error—is: h

in which

COt oJ —"bT/7—: ±COt d E sin a cos a E"=pitch diameter increment due to error in half angle

h=basic thread depth

a — basic half angle of thread

a' — error in half angle of thread The sign of cot a is plus when the half angle of thread is less than basic, and

minus when the half angle is greater than basic. By omitting ± cot a from

the formula an approximate mean value for a' or E" is obtained which differs very little from either extreme value. The commission has, therefore, adopted

for general use the formula:

cot a — —• E sin a cos a For threads of American National form this formula reduces to: cot a'=2§^

or $"=§P tan a' For the form of thread recommended for pipe-thread gages the formula becomes:

1.53812?

or cot a'— E

„

fl//^ 1-53812tftn , APPENDIX 2. WIRE METHODS OF MEASUREMENT OF

PITCH DIAMETER

Throughout this report emphasis has been placed on pitch diameter tolerances and limits, as upon these the fit of a screw thread largely depends. The maintenance of these tolerances and limits requires the use of limit thread gages, and

these, in turn, depend upon the absolute values or measurements of master

gages. The measurement of pitch diameter presents certain difficulties which

may result in an uncertainty as to its true value. The adoption of a uniform

practice in making such measurement is, therefore, desirable. The so-called "three-wire method" of measuring pitch diameter, as here outlined, has been

found to be the most accurate and satisfactory when properly carried out, and

is recommended for universal use in the direct measurement of thread-plug gages.

1. SIZE OF WIRES

In the three-wire method of measuring pitch diameter small hardened steel cylinders or wires of correct size are placed in the thread groove, two on one

side of the screw and one on the opposite side, as shown in Figure 54. The

contact face of the micrometer anvil or spindle over the two wires must be

sufficiently large in diameter to touch both wires; that is, it must be equal to

or greater than the pitch of the thread. It is best to select wires of such a size that they touch the sides of the thread at the mid slope, for the reason that the measurement of pitch diameter is least affected by any error in thread angle

which may be present when such size is used. The size of wire which touches

exactly at the mid slope of a perfect thread of a given pitch is termed the "bestsize" wire for that pitch. Any size, however, may be used which will permit
WIRE METHODS OF MEASUREMENT 185

the wires to rest on the sides of the thread and also project above the top of the thread. The depth at which a wire of given diameter will rest in a thread groove de- pends primarily on the pitch and included angle of the thread; and secondarily, on the angle made by the helix, at the point of contact of the wire and the

thread, with a plane perpendicular to the axis of the screw. Inasmuch as varia- tion in the helix angle has a very small effect in determining the diameter of the wire which touches at the mid slope of the thread, and as it is desirable to use one size of wire to measure all threads of a given pitch and included angle, the best size wire is taken as that size which will touch at the mid slope of a

groove cut around a cylinder perpendicular to the axis of the cylinder, and of

Fig. 54.

Three-wire method of measuring pitch diameter of thread plug gages the same angle and depth as the thread of the given pitch. This is equivalent to a thread of zero helix angle. The size of wire touching at the mid slope, or "best-size" wire, is given by the formula: G=P-sec a

in which

G—diameter of wire p—pitch a included angle of thread

This formula reduces to: 0.57735X2?, for 60° threads

It is frequently desirable, as, for example, when a best-size wire is not avail- able, to measure pitch diameter by means of wires of other than the best size. The minimum size which may be used is limited to that permitting the wire to
186 NATIONAL SCREW THREAD COMMISSION

project above the crest of the thread, and the maximum to that permitting the

wire to rest on the sides of the thread just below the crest, and not ride on the

crest of the thread. The diameters of the best size, maximum, and minimum

wires for American National coarse and fine threads are given in Tables 91 and 92.

2. SPECIFICATION FOR WIRES

A suitable specification for wires is as follows:

1. The wires should be cylinders of steel with working surfaces glass hard

and accurately finished.

2. The working surface should be about 1 inch in length, and the wire may

have a suitable handle which is provided at one end with an eye or other suitable means of suspension. One side of the handle, which should be flattened, should be marked with the pitch for which the wire is the best size, and with the diameter of the working part of the wire.

3. A suitable container should be provided for each set of wires, and if wires

are furnished without handles the pitch for which the wires are the best size and the diameter of the working part of the wires should be marked on the

container.

4. The wire should be round within 0.00002 inch and should be straight to 0.00002 inch over any quarter-inch interval.

5. One set of wires should consist of three wires which should have the same

diameter within 0.00003 inch, and this common diameter should be within

0.0001 inch of that corresponding to the best size for the pitch for which the wire

is to be used.

3. METHODS OF MEASURING AND USING WIRES

In order to measure the pitch diameter of a screw-thread gage to an accuracy

of 0.0001 inch by means of wires, it is necessary to know the wire diameters to 0.00002 inch. The micrometer to be used for measuring wires should be one which is graduated to ten-thousandths of an inch and upon which hundredthousandths of an inch can be estimated. Such micrometers are available in various forms of precision bench micrometers, and measuring machines. Care

should be taken to make sure that the measuring faces of the micrometer are

flat and parallel to within 0.00002 inch. The taper of wires can best be deter- mined by measuring between a flat micrometer contact and a cylindrical anvil. Any pits or worn spots on the wires can be detected with the same arrangement.

Variations in roundness and straightness are usually determined by rotating the

wire between flat contacts one-fourth inch in diameter. However, one form of variation in roundness can only be detected by rotating the wire in a V groove

against a flat micrometer contact. The V groove may be the thread space in a hardened and well-finished thread plug gage. The contact pressure used in making measurements is also an important

factor, since the wires, when in use, rest on the sides of the thread, and a given

pressure exerted on the top of the thread has a magnified effect in distorting the

wire and causing the measurement of the pitch diameter to be slightly less than

it should be. In making measurements over the wires inserted in the thread

groove, it has been common shop practice to hold the wires down into the thread by means of elastic bands. This has a tendency to prevent the wires from

adjusting themselves to the proper position in the thread grooves; thus a false measurement is obtained. In some cases it has also been the practice to support

the screw being measured on two wires, which are in turn supported on a hori- zontal surface, and measuring from this surface to the top of a wire placed in a

thread over the gage. If the screw is of large diameter, its weight causes a

distortion of the wires and an inaccurate reading is obtained. For these reasons
WIRE METHODS OF MEASUREMENT 187

these practices should be avoided and subsidiary apparatus for supporting the

wires and micrometer should be used. For consistent results a standard practice as to contact pressure in making

wire measurements of hardened screw thread gages is necessary. The computed value for the pitch diameter of a screw thread gage obtained from readings over wires will depend upon the accuracy of the measuring instrument

used, the contact pressure, and the value of the diameter of the wires used in the computations. The use of different contact pressures will cause a difference

| in the readings over the wires, and such errors can only be compensated by

the use of a value for the diameter of the wires depending on the contact pres- sure used. The effect of variation in contact pressure in measuring threads

of fine pitches is indicated by the difference in readings obtained with 2 and

5 pounds pressure on a 24-pitch thread plug gage. The reading over the wires with 5 pounds pressure was 0.00013 inch less than with 2 pounds pressure. A wire presses on the sides of a 60° thread with the pressure that is applied

to the wire by the measuring instrument. This fact would indicate that the diameter of the wire should be determined by readings made on the wire over

a hardened and lapped cylinder having a radius equal to the radius of curvature

of the helical surface of the thread at the point of contact, using the pressure

to be used in determining the pitch diameter of the gage. However, it is not

practical to employ such a variety of cylinders as would be required, and it is recommended for standard practice that wires be measured between a flat contact and a 0.750-inch hardened and accurately ground and lapped steel cylinder with the pressure used in measuring the pitch diameter of the gage. Furthermore, to avoid a permanent deformation of the material of the wires and gages it is necessary to limit the contact pressure. For pitches finer than

20 threads per inch a pressure of 8 ounces is recommended. For pitches of 20

threads per inch and coarser a pressure not exceeding 3 pounds is recommended.

Measurements of a thread plug gage made in accordance with these instructions, with wires which conform to the above specifications, should be accurate

to 0.0001 inch. If the diameters of the wires are known only to an accuracy of 0.0001 inch, an accuracy better than 0.0003 inch in the measurement of pitch

diameter can not be expected.

4. MEASUREMENT OF PITCH DIAMETER OF AMERICAN NATIONAL

STRAIGHT THREADS

The general formula for determining the pitch diameter .of any thread whose

sides are symmetrical with respect to a line drawn through the vertex and per- pendicular to the axis of the thread, in which the very slight effect of helix angle

is not taken into account, is

:

1 E=M->r~^-G (1 +cosec a)

i The general formula, in which the helix angle is taken into account, is: E=M-k~^—Q (1+cosec a-t-y cos a cot a) in which S= tangent of the helix angle. The value of S, the tangent of the helix angle, is given by the formula o, L 1 3.1416 E Z.imNE

in which T , , Z=lead N=number of turns per inch .E=nominal pitch diameter

In commercial practice the term cos a cot is neglected, as its value is small, being in all cases less than 0.00015 inch for standard fastening screws when the best-size wire is used, and the above formula takes the simplified form given above. This practice is permissible provided that it is uniformly followed, and in order to maintain uniformity of practice, and thus avoid confusion, the Bureau of Standards uses the latter —2~ cos a cot a ) exceeds 0.00015 inch, as in the case of Acme

and multiple threads, or other threads having exceptionally large helix angles. 18415°—29 13
188 NATIONAL SCREW THREAD COMMISSION

in which

E=pitch diameter

M=measurement over wires a =one-half included angle of thread n=number of threads per inch G=diameter of wires This formula differs from those given in most engineering handbooks in that the

latter, as generally given, yield a result which should check with the major

diameter of the screw measured, while the pitch diameter itself is not mentioned. For a 60° thread of correct angle and thread form this formula simplifies to

B=M+O 86603_3(? n

For a given set of best-size wires E=M-X

when * cot a X=G (1 + cosec a) 2n

The quantity X is a constant for a given thread angle, and, when the wires are used for measuring threads of the pitch and angle for which they are the best size, the pitch diameter is obtained by the simple operation of subtracting this constant

or factor from the measurement taken over the wires. In fact, when best-size wires are used, this factor is changed very little by a moderate variation or error

in the angle of the thread. Consequently, the factors for the various sets of wires

in use may be tabulated, thus saving a considerable amount of time in the inspec- tion of gages. However, when wires of other than the best size are used, this factor changes quite appreciably with a variation in the angle of the thread.

It has been shown that, with the exception of coarse pitch screws, variation in angle from the basic value causes no appreciable change in the quantity X for the

best-size wires. On the other hand, when a wire near the maximum or minimum

allowable size is used, a considerable change occurs, and the values of the cotangent

and cosecant of the actual measured half angle are to be used. It is apparent,

therefore, that there is a great advantage in using wires very closely approximating the best size. For convenience in carrying out computations, the values of

C

°2n

a

f°r standard pitches are given in Table 91.

5. MEASUREMENT OF PITCH DIAMETER OF AMERICAN NATIONAL

TAPER THREADS

The pitch diameter of a taper thread plug gage is measured in much the same manner as that of a straight thread gage, except that a definite position at which

the measurement is to be made must be located. A point at a known distance L from the end of the gage is located by means of a combination of precision gage blocks and the cone point furnished as an accessory with these blocks, as shown in Figure 55 at A. The gage is set vertically on a surface plate, the cone

point is placed with its axis horizontal at the desired height, and the plug is turned until the point fits accurately into the thread. The position of this point

is marked by placing a bit of Prussian blue or wax immediately above it. Measurement is made over the wires in the usual manner, but care must be

taken that the contact surfaces of the micrometer make contact with all three

wires, since the micrometer is not perpendicular to the axis of the screw when

there is proper contact. (See fig. 55.) On account of this inclination, the measurement over the wires must be multiplied by the secant of the half angle

of the taper of the thread. The formula for the pitch diameter of any taper
WIRE METHODS OP MEASUREMENT 189

thread plug gage, the threads of which are symmetrical with respect to a line perpendicular to the axis, then has the form: 2 E=M sec y+^~—G (1+cosec a) in which

E=pitch diameter

M—measurement over wires y

half angle of taper of thread n= number of threads per inch=l/p

a=half angle of thread G—diameter of wires

Fig. 55.

Measurement of pitch diameter of taper thread gages by the three-wire method Thus the pitch diameter of an American National standard pipe thread gage having correct angle (60°) and taper {% inch per foot) is then given by the formula: #=1.00048 M+0.86603 p-ZG

a See footnotes 16 and l, pp. 106, 187. In the above formula for the value of E, the term is an approximationifor the value of H. The exact value of His used when the value of the term

tan y^lia

- exceeds

0.00004 inch, which ordinarily occurs only on special taper threads of coarse pitch or steep taper.
190 NATIONAL SCREW THREAD COMMISSION

The pitch diameter at any other point along the thread, as at the gaging

notch, is obtained by multiplying the distance parallel to the axis of the thread,

between this point and the point at which the measurement was taken, by the taper per inch, then adding the product to or subtracting it from the measured

pitch diameter according to the direction in which the second point is located with respect to the first. The following method, illustrated in Figure 56, has a theoretical advantage

over the first method in that it is independent of the taper of the thread, and,

therefore, requires less computation; or if the taper is not measured but assumed

L

Til oc*S

U2JS//77

Fig. 56.

Measurement of pitch diameter of taper thread gages by the two-wire method

to be correct, it is more accurate. The axis of the gage and the line of meas- urement are constrained perpendicular to each other. This is easily done on a measuring machine if the gage is supported on centers mounted on a slide whose ways are perpendicular to the line of measurement. If a micrometer

caliper is used, its spindle is constrained perpendicular to the axis of the screw. One method is to place the gage on a surface plate with its axis vertical, and

support the micrometer in a horizontal position with its anvil and spindle resting on two equal combinations of gage blocks as shown in Figure 56 at A. A single wire is inserted in the thread at the point located as in the previous method, and

one other wire is placed in the upper thread on the opposite side. A measure- ment is taken over the two wires: the second wire is then moved to the thread
WIRE METHODS OF MEASUREMENT 191

immediately below, and a second reading is taken. The mean of these two

readings is substituted in any of the above formulas in the place of M sec y, or 1.00048 M.

6. MEASUREMENT OF PITCH DIAMETER OF THREAD RING GAGES

The application of direct methods of measurement to determining the pitch

diameter of thread ring gages presents serious difficulties, particularly in securing

I proper contact pressure when a high degree of precision is required. The usual

practice is to fit the ring gage to a master setting plug. When the thread ring gage is of correct lead, angle, and thread form, within close limits, this method is quite satisfactory and represents standard American practice. It is the only

method available for small sizes of threads. For the larger sizes, various more

or less satisfactory methods have been devised, but none of these have found

wide application.

Table 91.

Wire sizes and constants, American National coarse, fine, and pipe

threads

Wire sizes 1 Threads

per inch

71

Pitch Pitch Depth of V thread Best

0.577350p Maximum

1.010363p Minimum

0.505182p n

2 o 1 2~2n

cot 30° 2n

1 2 3 4 5 6 7

Inch

0.00722

.00802

.00902

. 01031

. 01203

Inch

0. 01263

. 01403

. 01579

.01804

. 02105

Inch

0. 00631 .00702 .00789

.00902

. 01052

80

72

64

5648

Inch

0. 01250

. 01389

. 01562

. 01786

. 02083

Inch

0. 00625

.00694

.00781

. 00893

.01042

0. 01083

. 01203

. 01353

. 01546 .01804

. 01312

. 01443 .01604

.01804

.02062

.02296

. 02526

.02807

. 03157

.03608

. 01148

. 01263

. 01403

. 01579 .01804

4440

36

3228

. 02273

.02500

. 02778

. 03125

. 03571

. 01136

.01250

. 01389

.01562 .01786

.01968

. 02165

. 02406 .02706

. 03093

. 02138

.02406

.02887

. 03208

. 03608

.03742

.04210

.05052

*. 05613

.06315

. 01871

. 02105

. 02526

.02807

. 03157

27

24

20

1816

. 03704

.04167 .05000

. 05556 .06250

. 01852

. 02083

.02500

.02778

. 03125

. 03208

. 03608 .04330

.04811 .05413

.04124

.04441

.04811 .05020

. 05249

. 07217

. 07772 .08420

. 08786

.09185

.03608

.03886 .04210

.04393 .04593

14

13

1211.5

11

. 07143

. 07692

.08333

. 08696

.09091

. 03571 .03846

.04167

.04348 .04545

.06186

. 06662

. 07217

. 07531

. 07873

. 05773 .06415

. 07217

. 08248 .09623

.10104

. 11226

. 12630

. 14434 .16839

. 05052

. 05613

.06315

. 07217 .08420

109

8

76

.10000

. 11111 .12500 .14286

. 16667

.05000 .05556

.06250

. 07143

.08333

. 08660

.09623

. 10825 .12372

. 14434 .11547

. 12830

. 14434 .16496

. 20207

.22453

. 25259 .28868

. 10104

. 11226 .12630

. 14434

5

4.5

43.5

.20000

.22222 .25000

.28571

.10000

. 11111 .12500

. 14286

. 17321

. 19245

. 21651 .24744

1 These wire sizes are based on zero helix angle. Also maximum and minimum sizes are based on a width of flat at the crest equal to HXp. The width of flat of American National pipe thread gages is slightly less than this, so that the minimum size listed is slightly too small for such gages. In any case, the use of wires of either extreme size is to be avoided.
192 NATIONAL SCREW THREAD COMMISSION

CO

i

i ix®

x®x

|

—

J

j X0XX

i

i ®xxx

<c

i 1 ® XXXX

i i <g>x xx i

00 X®XX X

—

X0XXX

o

— ! X 0XXXX

-4- XX® XXXX

11.5 XX<8>X XXXX

CM

I i X0XX XXXX

CO X®XXX XXX

^ 0XXXX XX

X® XXXXX X

00

r-l - -

;X0X XXXXX

;®XX XXXX

X&XXX X

CM X ®xxxx

$ xxxx

CO X®X XXX

CO X0XX XX

1 © X0XXX XX

X ®XXXX X

® XXXXX ;

<8>X XXX

X0XX XX

CM

t>. X0XXX X

o00 oxxxx

inches)

).00722 .00802 .00902 .01031 .01203 .01312 .01443

1

.01604

1

.01804.. .02062 .02138 .02887

I

.03208...

.03608....

J

.04124 .04441 .04811 .05020 .05249 .05773 .06415 .07217 .08248 .09623 .11547 .12830

1

.14434.... 3

!s
WIRE METHODS OF MEASUREMENT 193

7. WIRE METHODS OF MEASUREMENT OF THREAD THICKNESS OF

ACME THREADED PLUG GAGES

For threads having a thread angle less than 45° the quality of fit can be more

accurately controlled by checking the element of thread thickness, in relation to the basic major diameter (that is, the thread thickness at the nominal pitch

diameter), than by checking pitch diameter. For this purpose the three-wire method may be applied in the same manner as for measuring pitch diameter, but

the method of computation is slightly different. On account of the small thread

angle, the cotangent of which is large, it is always necessary to take the helix angle into account in measuring thread thickness by the three-wire method.

The general formula to be applied in determining thread thickness is as follows: S2 t=p—tan a [D—2B—M+G(l + cosec a+^cos a cot a)] in which

D== basic major diameter of screw Af= measurement over wires G= diameter of wires a= half angle of thread S= tangent of helix angle at pitch line P= pitch

B= depth at which thread thickness is measured

t= thread thickness at depth B

On Acme screw threads and the thread angle being 29°, the above formula reduces to

*=1.12931p+0.25862(M-D)-(?(1.29152 + 0.48407£2) The same formula applies to taps for Acme threads, although the major diameter

is larger than basic, since the formula is based on the basic major diameter. The diameters of the best size, maximum, and minimum wires for standard

pitches of Acme threads are listed in Table 93. Also, for convenience in carrying out computations, the values of 1.12931p and of 1. 29152 + 0.48407/S2 for various diameters and pitches of single, double, triple, and quadruple threads are given

in Tables 94, 95, 96, and 97. Table 93.

Wire sizes and constants, American National Acme threads {29°)

Threads per inch Pitch

1 Wire sizes '

Best

0.516450p Maximum0.650013© Minimum

0.487263p

1 2 3 4 5

1 Inch

1. 00000

.75000

. 66667 .50000 .40000

. 33333 .25000

.20000

. 16667 .12500 .10000

. 08333

Inch

0. 51645

. 38734

. 34430

. 25822

.20658

. 17215 .12911

. 10329

. 08608

.06456

.05164 .04304

Inch

0. 65001

. 48751 .43334

. 32501 .26001

. 21667

. 16250 .13000

. 10834

. 08125

.06500

.05417

Inch

0. 48726

.36545

.32484

. 24363

.19491 .16242

. 12182

. 09745

. 08121

.06091

. 04873

.04061

1H

VA - 22V2 - 34

56..

8.10

12

1 Based on zero helix angle,
194 NATIONAL SCREW THREAD COMMISSION

Table 94.—Values of 1.12981? and 1.29152+0. 48407S2 for various diameters and

pitches, Acme threads SINGLE THREADS

0. 09411 jo. 11293 0. 14116|'o. 18822|o. 22586|o. 28233jo. 37644|o. 45172|o. 56465|o. 7528?|o. 8469s|l. 12931

Threads per inch, n=l/p2V2 1.1293L?

1.291518+0.484074S2

1. 29458

1. 29478 314 394

277 252

233 220

209

201 194

189

181

175

171

168

165

163 162

161 160

159 158

157

157 156

156

156 155

155

155

155

154 154

154

154

154

154 154

154

153

153

153 153

153 153

153

153

153

153

153 152 152

152

152

152

152

152

152

152 152

152

152

1. 29152

165

163 162

161 160

159

159 158

157

157 157

156

156

156 155

155

155

155

155 154

154 154

154

154 154

154 153

153

153 153

153

153

153

153

153

153 153 153

152

152

152 152

152

152

1. 29152

L 29552

458

394 348

314

288 268

252

239 220

206

196

189

183

179 175 172

170

168

163 162

161

161 160

159

159 158

158

157 157

157 156

156 156

156

155

155

155 155 155

154

154

154 154 154

154

153

153

153

153 153

153

153

153

153

153

153

153 29153

369 1. 29478

339 314

277 252

233 220 209

201

194 189

184

181 178

175

173

171 169

165

164! 163

1631 162

161

161 160

160 159 159

158

158

1.58 157 157

156

156

156

155

155 155 155

154

154

154 154

154

154

154 154

153

153 153

1. 29153

159 158

157

157

157 156

156

156 155

155

155 155 155

154

154

154 154 154 29154

1. 29458

394 348

314

201

167 166

165

165

163 162

161

161

160

159 159

158

158

157

157 157 156

156

156

156

155

155 155

1. 29155

1. 29458 408

369

339

314

294

27264 252

242

233

226 220

214 209

205

201 19

194

191 189

187 184

183

181 179

178 176

175

173

171 169

168

167 165 164

163

163

162

161

161 160 160

159 159

158 158

158

1. 2915V

1. 29478

431

394

364' 339 1. 29458 318 423

165

164

163

163 162

161 161 160

1. 29160

1. 29458

431

3871 369 1. 29434 1 353 413

339j 394

326

1 377

314 362! 303 348

294 336

285j r 277' 270

264

257

165 29165 1

220

216

212

209 29175 1. 29182 1. 29206
WIRE METHODS OF MEASUREMENT 195

Table 95.— Values of 1.12931p and 1. 29152 +048407S2 for various diameters and

pitches, Acme threads DOUBLE THREADS

Threads per inch, n=l/p

Bssic m£ijor

HioTTipfpr UlaJ-LIC LCI (inches) »

1

8 • 1 ' 1 3 |

| ' 1 IV2 1 1.12931p

0. 0941l|o. 11293jo. 141ie|o. 18822 0. 22586|o. 28233j 0. 37644|o. 45172|o. 56465 0. 75287jo. 84698 1. 12931 1.291518+0.484074.S2 u

Me

1. 32291 1. 34056! 1. 37871

1. 31009 1. 31999:1. 34056 % 1. 30378 1.31009|1. 32291 1. 35558

7/ „ 1. 30021 1. 304581.313321. 33496 1. 36041 J4 6 tA 1 29800 1.30121 1. 30753 1 !. 32291 1. 34056 1. 37871 He 654 1. 29899' 1. 30378 1. 31525 1. 32820 1. 35558

5/i 552 745 1. 3012lll. 31009

1. 2993711. 30645

800! 1. 30378

1. 31999 1. 34056

114 ^^16* 478 635 1. 31425 1. 33027 1. 37188

423 552

489

1. 31009 1. 32291 1. 35558

13< <• 381 697 1. 30177 1. 30698 1. 31746 1. 34378 1. 37519 % :__ 348 440 616 1. 30021 1. 30458 1. 31332 1. 33496 1. 36041

lo/\6. - - - 322 401 369

552 1. 29899 1. 30271 1. 31009 1. 32820 1. 34923 300 501 800 1. 30121 1. 30753 1. 32291 1. 34056 1. 37871

1lys1A 268 322

288

423 369

654 1. 29899 1. 30378 1. 31525 1. 32820 1. 35558

1 Va 245 552 745 1. 30121 1. 31009 1. 31999 1. 34056 m 228 264 330 478 635 1. 29937 1. 30645 1. 31425 1. 33027 1. 37188 m 216 245 300 423 552 800 1. 30378 1. 31009 1. 32291 1. 35558 1. 37871

1 54 206 231 277 381 489 697 1. 30177 1. 30698 1. 31746 1. 34378 1. 36215

Lyi 198 220 259 348 440 616 1. 30021 1. 30458 1. 31332 1. 33496 1. 34989

1 76 L'/& 192 211 245 322 401 552 1. 29899 1. 30271 1. 31009 1. 32821 1. 34057 2 187 203 234 300 369 501 800 1. 30121 1. 30? 53 1. 32291 1. 33331 1. 37871 2H 183 197 224 283 343 458 720 1. 29999 1. 3054V 1. 31868 1. 32? 55 1. 36581

zy4 91/ 180 192 216 268 322 423 654 899 1. 30378 1. 31525 1. 32291 1. 35558

zy% 177 188 209 256 303 394 599 815 1. 30238 1. 31244 1. 31911 1. 34732 2U 174 184 203 245 288 369 552 745 1. 30121 1. 31009 1. 31596 1. 34056 251 172 181 198 236 275 348 513 686 1. 30021 1. 30812 1. 31332 1. 33496 2% 170

169

179 194 228 264 330 478 635 1. 29937 1. 30645 1. 31108 1. 33027

97,6 i5/8 176 191 222 254 314 449 590 864 1. 30502 1. 30917 1. 32630

3 167 174 187 216 245 300 423 552 800 1. 30378 1. 30753 1. 32291 *M 1 ftft 1DD 173 184 211 238 288 401 519 745 1. 30271 1. 30611 1. 31999

3*4 165 171 182 206 231 277 381 489 697 1. 30177 1. 3048? 1. 31746 3H-— — 164 170 180 202 225 268 364 463 654 1. 30094 1. 30378 1. 31525

163 168 178 198 220 259 348 440 616 1. 30021 1. 30282 1. 31332 078 162 167 176 195 215 252 334 419 582 1. 29957 1. 30197 1. 31161

162 166 174 192 211 245 322 401 552 899 1. 30121 1. 31009 3% 161 165 173 190 207 239 310 384 525 847 1. 30053 1. 30874 4 160 164 172 187 203 234 300 369 501 800 1. 29992 1. 30753

414 4ys 160 164 170 185 200 228 291 356 478 ?58 937 1. 30645 4U3/4 159 163 169 183 197 224 283 343 458 720 887 1. 30547

436 162 168 181 195 220 275 332 440 686 842 1. 30458 4^ 159 162 167 180 192 216 268 322 423 654 800 1. 30378 m 158 161 167 166

178 190 212 261 312 408 625 763 1. 30305

43/ 158 161 177 188 209 256 303 394 599 728 1. 30238

47/6 158 160 165 176 186 206 250 295 381 575 1. 30177

c 157 160 164 174 184 203 245 288 36S 552 668 1 30121

5j4 157 159 163 172 181 198 236 275 348 513 616 1. 30021 5H 156 158 162 170 179 194 228 264 330 478 572 1. 29937

156 158 161

160

169 176 191 222 254 314 449 534 864

g 156 15? 167 174 187 216 245 300 423 501 800

0/4 155 157 160 166 173 184 211 238 288 401 472 745 m 155 157 165 171 182 206 231 277 381 446 697 6% 155 156 I5i 164 170 180 202 225 268 364 423 654

1 155 156 158 163 168 178 198 220 259 348 403 616 fe—- - 154 156 158 162 167 176 195 215 252 334 385 582

7^2 - 154 155 157 162 166 174 192 211 245 322 369 552 7% 154 155 157 161 165 173 190 207 239 310 355 525

8 154 155 157 160 164 172 187 203 234 300 342 501 8K 154 155 156 16C 164 170 185 200 228 291 330 478 m 154 155 156 15S 163 169 183 197 224 283 319 458 8% 154 154 156 15S 162 168 181 195 220 275 309 440

9 152 154 156 156 162 167 180 192 216 268 30C 423 QH 152 154 15£ 15« 161 167 178 190 212 261 292 408 m .— 15S 154 15£ 158 161 166 177 188 209 256 284 394 9% 155 154 15£ 158 16C 165 176 186 206 25C 277 381

10 1. 2915C 1. 29154 1. 2915£ 1. 2915? 1. 2916C 1. 29164 1. 29174 1. 29184 1. 29203 1. 29245 1. 29271 1. 29369

1
196 NATIONAL SCREW THREAD COMMISSION

Table 96—Values of 1.12931p and 1. 29152 +0484.07S2 for various diameters and

pitches, Acme threads TRIPLE THREADS

Threads per inch, n=l/p

12 ,0 8 6 « 1 • 1 • 2Y2 iy2 IX. 1 Basic major

diameter 1.12931p

(inches)

0. 09411 0. 11293|0. 14116 0. l8822|o. 22586 0. 28233 0. 37644 0.45172 0. 56465|o.75287|o. 84698 1. 12931 1.291518+0.484074S2

1. 36215 1. 40187 1. 48771 Me - l! 33331 l! 35558 l! 40187 n 1. 31911 1. 33331 L, 36215 1. 43565

1. 31108 l! 32092 1. 34057 l! 38927 1. 44653

Yi L 30611 1. 31332 L 32755 1. 36215 L 40187 L 48771

1. 30282 1 30832 h 31911 1. 34492 1. 37406 L 43566 *A l! 30053 L 30487 1. 31332 L 33331 L 35558 L 40187 ma 1 29887 1. 30238 l! 30918 L 32511 L 34267 L 37871 L 47233

94 763

668

l! 30053 1. 30611 L 31911 L 33331 1. 36215 1. 43566 Wia 1. 29911 1. 30378 t 31458 L 32630 1. 34989 L 40911 1. 47978

593 800 1. 30197 1. 31108 L 32092 1. 34057 1. 38927 1. 44653

15A6 534 712 l! 30053 l! 30832 l! 31669 1*. 33331 1. 37406 1. 42137

l 486 641 l! 29937 1 30611 1. 31332 L 32755 1. 36215 1. 40187 1. 48771 m 413 534 763 L 30282 L 30832 1. 31911 1. 34492 1. 37406 L 43566 m. 362 458

403

641 L 30053 h 30487 1. 31332 1. 33331 1. 35558 1. 40187 i% 324 552 L 29887 1. 30238 1. 30918 1. 32511 1. 34267 1. 37871 1. 47233 m - 296 362 486

434

763 668

l! 30053 l". 30611 1. 31911 L 33331 1. 36215 1j.. 4^^^ Ttomjo 1. 48771 m 274 330 L 29911 L 30378 1. 31458 1. 32630 L 34989 1 40911 1. 45043 in~- 257 305 394 593 800 1. 30197 1.' 31108 1.' 32092 1. 34057 1. 38927 1. 42285 m - 243 284 362 534 712 1. 30053 L 30832 1. 31669 1.33331 1. 37406 1. 40188

2 232 268 336 486 641 1. 29937 1. 30611 1. 31332 1. 32755 1 385 t

;

, X. tJOOUuS 1. 48771 2H 222 254 314 446 582 842 i. oyrroi. l! 31058 1. 32291 1. 35263 1. 37260 1. 45868 2H 215 243 296 413 534 763 1. 30282 1. 30832 1. 31911 l! 34492 1. 36214 1. 43566 2% 208 233 281 385 493 697 L 30158 1. 30645 1. 31596 1. 33858 1. 35359 1. 41708 m— —

-

203

198 225 268 362 458 641 1. 30053 1. 30487 1. 31332 1.33331 1.34650 1. 40187 2% 218 257 342 429 593 1. 29963 1. 30353 1. 31108 1. 32887 1. 34056 1. 38927 m~ —

-

194 212 247 324 403 552 887 1. 30238 X. OUC7XO 1. 32511 1. 33554 1. 37871 2% 190 207 239 309 381 517 820 1. 30139 1 30753 1. 32189 1 33125 1. 36977

3 187 203 199 232 296 362 486 763 1. 30053 1. 30611 l! 31911 L 32755 l! 36215 3H 184 225 284 345 458 712 1. 29977 1. 30487 1. 31669 L 32435 1. 35558 3H 182 195 220 274 330 434 668 911 X. o\jo 1 o 1. 31458 1. 32156 1. 34989 3% 179 192 215 26S 316 413 628 852 1. 30282 1. 31272 1. 31911 1. 34493 m 177 189 210 257 305 394 80C 1. 30197 1. 31108 1. 31694 1 34056 3H 176 186 206 250 294 377 562 754 l! 30121 1. 30962 1. 31502 L 33672

3?4 174 184 203

199

243 284 362 534 712 1. 30053 1. 30832 L 31332 1. 33331

3£6 173 182 237 276 348 508 675 1. 29992 1. 30716 1. 31179 1. 33027

4. 171 18C 196 232 268 336 486 641 937

887

1. 30611 1. 31041 1. 32755 m — 170 178 194 227 261 324 465 610 X. OwlU 1. 30917 1. 32511 4H 169 177 191 222 254 314 446 582 842 1. 30431 1. 30805 1. 32291 4%~- 168 175 189 218 248 305 429 557 800 1. 30353 1. 30704 1. 32091 4W 167 174 187 215 243 296

288

413

399

534 763 1.1 ^n9£9 OUZoZ 1. 30611 1. 31911 m 166 I/O 185 21] 238 513 738 1 30217 1. ovozv 1. 31746

4?4.. 166 172 183 208 233 281 385 493 697 L 30158 1. 30449 x. oxoyo m 165 171 182 205 229 274

268

373 475 458

668 1. 30103 1. 30378 1. 31458

5.... 164 170 180 203 225 362 641 1. 30053 1. 30313 L 31332

oyi 163 168 177 198 218 257 342 429 593 1. 29963 1. 30197 1. 31108 5H 162 167 175 194 212 247 324 403 552 887 1. 30097 1.30918 5% 161 165 173 190 207 239 309 381 517 820 1. 30011 1. 30753

6 160 164 171 187 203 232 296 362 486 763 1. 29937 1. 30611

6*4 160 163 170

168

184 199 225 284 345 458 712 871 1. 30487

159 162 182 195 • 220 274 330 434 668 814 1. 30378

694 159 162 167 179 192 215 265 316 413 628 763 1. 30282

7 158 161

160 166 177 189 210 257 305 394 593 717 1. 30197 7H 158 165 176 186 206 250 294 377 562 677 1. 30121

157 160 164 174 184 202

199 243 284 362 534509

641 1. 30053 7% 157 159 163 173 182 237 276 348 608 1. 29991

8 157 159 163 171 180 196 232 268 336 486 579 937

8*4 156 158 162 170

169 178 194 227 261 324 465 552 887 m~— 156 158 162 177 191 222 254 314 446 528 842 m 156 158 161 168 175 189 218 248 305 429 506 800 9 156 157 160 167

166 174 187 215 243 296 413 486 763 m~~ 155 157 160 173 185 211 238 288 399 467 728 m. 155 157 160 166 172 183 208 233 281 385 450 697 994— 155 156 159 165 171 182 205 229 274 373 434 668

10... 1. 29155 1. 29156 1. 29159 1. 29164 1. 29170 1. 29180 1. 29202 1. 29225 1. 29268 1. 29362 1.29420 1. 29641
WIRE METHODS OF MEASUREMENT 197

Table 97.—Values of 1.12931-p and 1. 29152+0484.07 for various diameters and

pitchesj Acme threads QUADRUPLE THREADS

Basic major

diameter

' (inches)

12 ) 10 • 5 | 4 3 | 2^ | 2

\ iy2 \ IX 1 1.12931p

0. 09411 [o. 11293 0.14116 0. 18822|o. 22586|o. 28233|o. 37644|o. 45172|o. 56465|o. 75287|o. 84698 1. 12931

Threads per inch, n=l/p

1.291518+0.484074&2

\i 1. 41708 1. 48771

1. 40540

1. 36581

1. 34378

1. 33027

1. 32139

1. 31525

1. 31083

1. 30753

1. 30502

1. 30305

1. 30148

1. 30021

1. 29831

697 599

525 468

423 387

1. 64030

1. 48771

1. 41708

1. 37871

1. 35558

1. 34056

1. 33027

1. 32291

1. 31746

1. 31332

1. 31009

1. 30753

1. 30547

1. 30238

1. 30021

1. 29864

745

654 582

525

Me 1. 36582

1. 34057

1. 32630

1. 31746

1. 31161

1. 30753

1. 30458

1. 30238

1. 30069

1. 29937

H 1. 54776

1. 46530

1. 41708

1. 38646

1. 36581

1. 35124

1. 34056

1. 33252

1. 32630

1. 32139

1. 31746

1.31161

1. 30753

1. 30458

1. 30238

1. 30069

1. 29937 831

Me 1. 56710

1. 48771

1. 43827

1. 40540

1. 38246

1. 36581

1. 35335

1. 34378

1. 33627

1. 33027

1. 32139

1. 31525

1. 31083

1. 30753

1. 30502

1. 30305

1. 30148

- 1. 64030

1. 54776

1. 48771

1. 44653

1. 41708

1. 39529

1. 37871

1. 36581

1. 35558

1. 34056

1. 33027

1. 32291

1. 31746

1. 31332

1. 31009

1. 30753

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2 294 358 478 745 1. 30021 1. 30547 1. 31746 1. 33027 1. 35558 1. 41708 1. 45868 1. 64030 2H 277 334 440 675 1. 29917 1 30378 1. 31425 1. 32540 1. 34732 1. 40017 1. 43566 1. 58870 2U 263 314 408 616 831 1. 30238 1.31161 1. 32139 1. 34056 1. 38646 1. 41708 1. 54776 m 252 297 381 567 758 1. 30121 1. 30940 1. 31806 1. 33496 1. 37519 1. 40187 1. 51473 2H— 242 283 358 525 697 1. 30021 1. 30753 1. 31525 1. 33027 1. 36581 1. 38927 1. 48771 2% 233 270 339 489 644 1. 29937 1. 30595 1. 31287 1. 32630 1. 35793 1. 37871 1. 46530 2% 226 259 322 458 599 864 1. 30458 1 31083 1. 32291 1. 35124 1. 36977 1. 44653 2% 220 250 307 431 559 800 1. 30341 1. 30907 1. 31999 1. 34551 1. 36215 1. 43064 3 214 242 294 408 525 745 1. 30238 1. 30753 1. 31746 1. 34056 1. 35558 1. 41708

209 235 283 387 495 697 1. 30148 1. 30619 1. 31525 1. 33627 1. 34989 1. 40540 2H 205 228 272 369 468 654 1. 30069 1. 30502 1. 31332 1. 33252 1. 34493 1. 39529

Z

3A 201 223 263 353 444 616 1 29999 1. 30397 1. 31161 1. 32922 1. 34056 1. 38647

197 218 256 339 423 582 937 1. 30305 1. 31009 1. 32630 1. 33672 1. 37871 m 194 213 248 326 404 552 881 1. 30222 1. 30874 1. 32371 1. 33331 1. 37188 3%. 191 209 242 314 387 525 831 1. 30148 1. 30753 1. 32139 1. 33027 1. 36581 Z% 189 205 236 303 372 501 786 1. 30081 1. 30645 1. 31932 1. 32755 1. 36041

4 187 202 231 294 358 478 745 1 30021 1. 30547 1. 31746 1. 32511 1. 35558 4^ 184 199 226 285 346 458 708 1. 29967 1. 30458 1. 31578 1. 32291 1. 35124 Wi 183 196 222 277 334 440 675 917 1. 30378 1. 31426 1. 32091 1. 34732 4H— 181 194 218 270 324 423 644 872 1. 30305 1. 31287 1. 31911 1. 34377 4H 179 191 214 264 314 408 616 831 1. 30238 1. 31161 1. 31746 1. 34056

178 189 211 257 305 394 591 793 1. 30177 1. 31045 1. 31595 1. 33764

43/4 176 187 208 252 297 381 567 758 1. 30121 1. 30940 1. 31458 1. 33495 m 175 186 205 247 289 369 545 726 1. 30069 1. 30843 1. 31331 1. 33251

5. 174 184 202 242 283 358 525 697 1. 30021 1. 30753 1. 31215 1. 33027

634- 172 181 197 233 270 339 489 644 1. 29937 1. 30595 1. 31009 1. 32630

170 178 193 226 259 322 458 599 864 1. 30458 1. 30832 1. 32291

6?4 6

169 176 190 220 250 307 431 559 800 1. 30340 1. 30680 1. 31999

167 174 187 214 242 294 408 525 745 1. 30238 1. 30547 1. 31746 6H 166 172 184 209 235 283 387 495 697 1. 30148 1. 30431 1. 31525 6H 165 171 181 205 228 272 369 468 654 1. 30069 1. 30329 1. 31332

164 169 179 201 223 263 353 444 616 1. 29999 1. 30238 1. 31161

163 168 177 197 218 256 339 423 582 937 1. 30157 1.31009 7H 162 167 175 194 213 248 326 404 552 881 1. 30086 1. 30874 7^ 162 166 174 191 209 242 314 387 525 831 1. 30021 1. 30753

734 161 165 173 189 205 236 303 372 501 786 1. 29963 1. 30644 8 160 164 171 187 202 231 294 358 478 745 911 1. 30547 m 160 163 170 184 199 226 285 346 458 708 863 1. 30458 m 159 163 169 183 196 222 277 334 440 675 821 1. 30378 8H_... - 159 162 168 181 194 218 270 324 423 644 781 1. 30305

9 _ 159 162 167 179 191 214 264 314 408 616 745 1. 30238

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9?4 158 160 165 175 186 205 247 289 369 545 654 1. 30069

10 1. 29157 1. 29160|1. 29164 1. 29174 1. 29184 1. 29202 1. 29242 1. 29283 1. 29358 1. 29525 1. 29629 1. 30021
198 NATIONAL SCEEW THREAD COMMISSION

APPENDIX 3. CONTROL OF ACCURACY OF THREAD ELEMENTS IN THE PRODUCTION OF THREADED PRODUCT

In order to maintain the dimensions of threaded product within the limiting

sizes specified, it is essential that the tools used and the processes applied be

suitable for the particular requirements. An analysis of the various factors controlling the accuracy of the individual thread elements is here presented. In

this analysis, the fundamental factors controlling the accuracy of the elements of a screw thread are stated, and are followed by a brief discussion of the relationship

of these factors to each of the prevailing commercial methods of producing screw

threads. It is recognized, however, that certain varying factors are involved,

such as lubrication, method of holding the work or tool, sharpness of cutting

edges, etc., so that it is not always possible to predetermine the exact sizes of the tools required to accomplish the desired results. Screw threads are usually produced either by cutting or rolling. Five general

methods of cutting, two of rolling, and two of finishing screw threads are in*com- mon use.

1. FUNDAMENTAL FACTORS

The accuracy of the individual elements of a thread is controlled mainly as follows

:

Angle by the angle between, and contour of the cutting edges of the tool used

for cutting, or of the sides of the grooves of the die used for rolling. Lead by the rate of the longitudinal motion of the tool with respect to the rate

of revolution of the part to be threaded. Major diameter of external thread by the outside diameter of the stock, or by

the forming tool. Minor diameter of internal thread by the diameter of the hole in the work before threading. In the case of a drilled hole, this depends on the diameter and accu- racy of grinding of the tap drill used.

Pitch diameter by the radial setting of the forming surface of the tool. Thread form by the form and position of the tool, and the conditions under which

it is used. Inspection of the angle and profile of the thread-forming tool is essential to control the accuracy of the thread produced. The same means and methods can

be applied to such inspection as are applied in the measurement of screw-thread

gages and threaded product. Attention is directed to the optical projection

apparatus for measuring angle and lead, and examining profile; the microscope,

which m&y be readily adapted to shop requirements; and indicating gages, which

may be designed to check the dimensions of threading tools. The sources of lead errors require special consideration and for this purpose the methods of producing screw threads may be considered under two headings,

namely, those in which relative longitudinal motion of the tool and product is controlled by means of a lead screw and those in which the tool is self-leading.

(a) Tool Controlled by Lead Screw.—In cutting a thread on a lathe or other machine embodying a lead screw, using a single point cutting tool or single

mining cutter, progressive lead errors are caused by (1) a progressive lead error

in the lead screw; (2) lack of parallelism of the motion of the cutting tool, the

axis of the lead screw, and the axis of the part to be threaded; and (3) incorrect

ratio of the rate of revolution of the spindle to that of the lead screw, due to an

incorrect or approximate combination of gears. Local lead errors are caused by (1) local lead errors in the lead screw; (2) lost motion in the action of the lead screw or connecting mechanism; (3) varying

frictional resistance in the mechanism; (4) when a live center is used, irregular
CONTROL OF ACCURACY IN PRODUCTION 199

play of its spindle in the bearings; and (5) variations in the amount of metal

removed by the cutting tool. Periodic lead errors are caused by (1> periodic lead errors in the lead screw;

(2) eccentricity of motion of the lead screw; (3) thrust bearings of spindle or

lead screw running out of true; (4) variations in the spacing of gear teeth, or

eccentric gears or mountings; (5) when a live center is used, eccentricity of motion

of its spindle; and (6) periodic variations in the amount of metal removed, due to

lack of uniformity of the material in diameter, straightness, or physical properties.

When a multiple-toothed threading tool is controlled by a lead screw, vari- ations from correct spacing of the teeth of the tool are superimposed on the lead

errors resulting from any of the above causes in that portion of the thread not

passed over by every tooth of the tool. In the portion of the thread completely

passed over by the tool, the effect of the difference in lead between the tool and

lead screw is to produce a thin thread. The simplest method of inspecting a machine tool to determine whether it will cut a screw thread within satisfactory limits is to cut carefully a sample

screw on the machine and measure the lead errors of the screw. The obvious

remedy for errors from such sources is the careful inspection of the various elements of the machine, and correction of the errors thus located, either by

improving the design or by carefully refinishing or remaking the parts to a greater

degree of accuracy.

(6) Self-Leading Threading Tool.—When a thread is cut by means of a

tap or die, which, as ordinarily used, are self-leading and not controlled by a lead

screw, lead errors may occur as the result of (1) incorrect lead of the tap or die;

(2) too much or too little relief at the throat of the die or on the chamfer at the end of the tap; (3) the setting of an adjustable die or tap chaser to cut a thread

considerably larger or smaller than that for which the tool was intended—that is, to cut a helix angle considerably different from the helix angle of the chaser;

(4) excessive resistance to longitudinal motion; (5) improper alinement of the

axis of the tap or die with that of the work, etc.; and (6) excessive angle relief. The control of accuracy of the lead of the tap or of the chasers in the die is the most difficult of these sources of error, and indeed presents serious difficulties. There is, first, the difficulty of cutting a tap or chaser which is free from lead

errors resulting from any of the causes outlined above; and second, the distortion which the steel composing the tap or die undergoes in hardening. In the inspection of such thread-forming tools practically the same means and

methods can be applied as in the measurement of screw-thread gages. For

checking the lead, indicating gages or some of the usual lead-measuring devices

for screw-thread gages may be used. To measure the lead of a die chaser, the

chaser must be held in a fixture in such a position that the direction of measure- ment corresponds to the direction of longitudinal motion of the chaser threads when cutting a thread.

2. CUTTING OF SCREW THREADS

(a) Single-Point Tool.—A screw thread may be produced by traversing a

single-point threading tool—shaped to correspond to the shape of the thread

space in an axial plane, and so placed as to cut an angle, equal to the angle of the top surface of the tool, in correct relation to the axis of the thread—along

the revolving part to be threaded at such a rate as to produce a thread of the

desired lead. This is the common method of cutting screws in an engine lathe, a lead screw driven by gearing being the usual means for imparting to the tool the longitudinal motion at the desired rate. This method is used commercially

only when special conditions make it necessary, as when the thread to be cut is not standard, or it is not practicable to apply other methods.
200 NATIONAL SCREW THREAD COMMISSION

Various forms of single-point cutting tools for cutting threads of American

National form are illustrated in Figure 57 at A, B, C, and D. The circular tool shown at C has the advantage that it can be reground indefinitely without

destroying its correct form. The diagram at D shows the method for calculating the angle X of the cutting tool, having a clearance angle V, in a plane perpendicular to the edge MN; and the formula for determining the clearance angle V,

of a tool for cutting a thread of helix angle s, is also given. Such tools usually

consist of hardened tool steel, ground to the correct form after hardening; special

alloys such as " stellite" are also used for this purpose.

(6) Thread Chaser.—A screw thread may be produced by successively

traversing a multiple-point thread tool, known as a chaser, along the part to be

tan JC = fa.n.CL See V

tan V -~ fa/rS CoTcl

D

Fig. 57.

Single -point and multiple point thread cutting tools threaded, each tooth following in the thread in the same manner as a single-point thread tool. Two forms of chasers are shown in Figure 57 at E and F, the one

at F being especially suitable for cutting fine threads. Chasers are well adapted

to roughing out threads, as they cut rapidly, and may be used for finishing threads accurately if the teeth are ground after hardening.

(c) Tap or Die.—A screw thread may be produced by using a tap for internal threads or die for external threads. These tools occur in considerable variety in

their commercial forms, but consist essentially of a number of multiple-point

cutters or chasers, usually four, arranged circumferentially. They may be

either solid or adjustable, and collapsible or self-opening, respectively, for with- drawing quickly from the work after threading. By their use a thread is generally

finished by one passage of the tool, although a second or finishing cut is some-
CONTROL OF ACCURACY IN PRODUCTION 201

times made to secure greater accuracy. Dies are applied, in general, to threading

screws, bolts, and studs; and taps to nuts or other internal threads within the

usual range of sizes. They are also applied to the threading of pipe and pipe

fittings. The rapidity with which threading operations may be performed by

the use of taps and dies, within the limits of accuracy suitable for a large per- centage of commercial work, makes them most efficient and widely used threading

tools. It is only in cutting large sizes or coarse pitches, or where a high degree

of accuracy is desired, that their use may be less economical than other means of cutting threads. Aside from lead errors, which have been previously considered, the accuracy

of the thread produced depends on the form of the cutting teeth, character of the

cutting edges, clearance or relief for cutting edges, construction of the tool, and

the conditions under which it is used.

(d) Milling Cutter.—A screw thread may be produced by feeding in to the depth of the thread and then traversing a rapidly revolving single milling cutter along the slower revolving part to be threaded at such a rate as to produce a

thread of the desired lead; the profile of the cutting edges of the cutter conforming approximately to the shape of the thread groove in an axial plane, and the axis

of the cutter being set at an angle to the axis of the thread, in a plane parallel to the axis of the thread, equal to the mean helix angle of the thread cut. The

single-cutter method of thread milling is especially applicable to the cutting of large threads of coarse pitch, multiple threads, and the heavier classes of work.

When the amount of metal to be removed is large, as compared with the size of the screw, this method is especially suitable because the torsional strain is much

smaller than that produced by a die, and consequently the accuracy of the screw produced is greater.3 (e) Threading Hob.—A screw thread may be produced by feeding in to the depth of the thread, and then traversing a rapidly revolving multiple milling cutter or thread hob, somewhat longer than the length of the thread to be cut

which consists of annular rows of teeth, whose centers lie in planes perpendicular

to the axis of the cutter (in effect a series of single cutters formed into one solid piece) , and the axis of which is parallel to the axis of the thread—along the slowly

revolving part to be threaded slightly more than either one or two complete

revolutions of the work, at a rate per revolution of the work equal to the pitch

of the thread. The multiple-cutter method of thread milling is used largely for cutting comparatively short threads, usually of fine or medium pitches, when

smoothness or a considerable degree of accuracy is desired, or when the thread must maintain a fixed relation with a point or surface on the work. The error introduced in the form of thread produced by cutter teeth having the same form as that of the intended form of thread, as the result of the axes of cutter and thread being parallel, is usually not serious except when the helix angle is large. 4 3. ROLLING OF SCREW THREADS

The second general process for forming screw threads—namely, that of rolling

is a cold-forging process. It may be defined as an impression or displacement

method whereby the threads are formed by means of a die or roll having threads

3 For refinements in connection with the determination of the profile of cutting edge of a thread milling

cutter, see The Milling of Screw Threads and Other Problems in the Theory of Screw Threads, by H. H.

Jeffcott. Proceedings of the Institution of Mechanical Engineers, 1922-1, pp. 515-528, and discussion pp.

529-562; or Engineering (London), 113, Apr. 7, 1922, pp. 441-442, and discussion pp. 412-414.

* For formulas which may be applied in such cases to determine and plot the exact contour of the cutting edges to produce, as nearly as possible, the thread form required, see Side-Cutting of Thread Milling Hobs, by Earle Buckingham. Transactions of thelAmerican Society of Mechanical Engineers, 43, 1920, pp.

569-593; also the reference cited in footnote^, p. 201, for thread milling cutter profile.
202 NATIONAL SCREW THREAD COMMISSION

or ridges, which are forced into the material to be threaded, and, by displacing

it, produce a thread of the required form and pitch. In this process no material

is removed, but the metal is displaced from the thread space and forced up on

each side above the original surface of the piece to be threaded. Thus, the major

diameter of a v-shaped 60° thread so produced is found in practice to be greater

than the original diameter of the blank by an amount varying from 65 per cent

of the single depth of thread for small screws to 85 per cent for large screws. An

approximate formula, based on geometrical considerations only, for the diameter

of a blank to be threaded to American National form is as follows: D1 =^D2 — l.SDp+ 0.63P3 in which

Di =diameter of blank

D «= major diameter of thread p =pitch of thread In case the thread required must be accurate within close limits, the exact value

of Di necessary in any given case must be determined experimentally, as its value is affected by the physical properties of the material.5 The thread-rolling process is the most rapid and economical method of forming

screw threads in quantity production, when the part to be threaded is of such

form as to permit its use. It is used only for external threads and is not regarded

as being feasible for internal threads, since the area of contact of the roll in an

internal thread is relatively much larger than on an external thread, and in order

to displace the metal a very heavy pressure is required. It is difficult to support

the work with the necessary rigidity to withstand the heavy pressure, and to provide a bearing for the roll which will withstand the strain. Screw threads may be rolled by either of two methods, as follows:

(a) Threading Roll.—By forcing a cylindrical disk or roll, having a threaded

periphery and being free to rotate on the pin or bolt on which it is mounted,

against the piece to be threaded while the latter is revolving. The cylindrical

roll is used when the work is in an automatic screw machine or turret lathe, and it

is impossible to cut the thread required by means of a thread cutting die, or when

an additional operation would be necessary before cutting the thread. The

thread on the roll corresponds in pitch, and approximately in form, to the thread

to be rolled. The roll may be presented to the work in either a tangential direc- tion as shown at A, Figure 58, or radially as shown at B; a satisfactory thread is formed in either case.

(6) Thread Rolling Dies.—By rolling the blank between dies, which may be

either flat or cylindrical in form, when performed by machines designed exclusively

for this work. When flat dies are used, as shown in Figure 58 at C, one die M

remains stationary and the other die, N, which is parallel or nearly parallel to M, has a reciprocating movement. The faces of the dies have parallel milled or planed grooves of approximately the same form as that of the required thread which are set at an angle to the line of motion of the blank equal to the helix angle

of the thread to be produced. The angles of the grooves and ridges in a plane

perpendicular to the direction of the grooves are given by the formula: Tan ai =tan a cos s in which

Oi =half angle of ridge of die a =half angle of thread to be rolled

s = helix angle of thread

* This formula is derived in Size of Stock for Bolts Having Rolled Threads, by F. Webster. American

Machinist, 30, Oct. 31, 1907, p. 630.
CONTROL OP ACCURACY IN PRODUCTION 203

The spacing of the ridges is determined by the formula:

Pi = p cos s in which =spacing of ridges of die p =pitch of thread to be rolled

s =helix angle of thread The blank is inserted at one end of the stationary die, and rolls between the

> die faces until it is ejected at the other, the thread being formed in one passage

of the blank. When cylindrical dies are used, one of the dies, which is a complete

cylinder, revolves continuously in one direction and the other is a stationary

cylindrical segment. This method is used extensively for threading almost all forms of small and medium sizes of screws and bolts, when required in suffi- ciently large quantities to warrant the use of a thread rolling machine.6 A

Fig. 58.

Methods of rolling screw threads

4. FINISHING OF SCREW THREADS

On account of the difficulty of producing an accurately finished thread by means

of a cutting tool, in ordinary gage-making practice the thread is ground, lapped,

or ground and lapped, in order to finish all elements of the thread to correct dimensions. The process of grinding is applied to hardened screws only, and is intended to correct any errors present as the result of distortion in the hardening

process, as well as those resulting from the cutting operation. Lapping is usually

applied to hardened screw threads, and may be either substituted for grinding,

or performed after grinding to remove the marks left by the grinding wheel and to produce a smooth and highly finished surface. These processes are used largely

in the production of screw-thread gages.

(a) Grinding.—The grinding of a thread is similar to the process of milling a thread by the single-cutter method. The profile of the periphery of the grinding wheel is " dressed" by means of a diamond to conform to the shape of the thread groove in an axial plane, with the axis of the wheel set at an angle to the

axis of the thread, in a plane parallel to the axis of the thread, equal to the helix

• The principles involved in determining the spacing and angle of ridges of flat dies, and position of the

dies, are considered in Principles of Thread Rolling and the Setting of Dies, by J. F. Springer, American

Machinist, 33, Apr. 21, 1910, pp. 739-741. 18415°—29 14
204 NATIONAL SCREW THREAD COMMISSION

angle. In order to produce a thread having straight sides and correct angle, the periphery of the wheel should be dressed to the required angle after the wheel

has been set to the helix angle, in the plane containing the axis of the thread and the center of the wheel. The same considerations as to the exact profile of the periphery of the grinding wheel, to produce a thread of exactly correct form,

apply as for the tooth profile of a single milling cutter set at the helix angle of the

thread. The principal differences between the thread milling and grinding processes are that a large diameter of grinding wheel is desirable, and several light cuts are taken, whereas, a small diameter of milling cutter is desirable and a

single cut is taken.

(6) Lapping.—The lapping of a screw thread may be defined as a process

of abrasion by successively traversing the thread, as it revolves, with a so-called

lap, which consists of an engaging screw thread of softer material, usually fine- LAP

THRS.AO

a a

Fig. 59.

Thread form of laps for lapping screw threads grained cast iron, brass, or cold-rolled steel, in which very fine abrasive material

is embedded in the thread surface. For removing considerable material, the

laps are charged with coarser abrasive, and for imparting fine finish, a finer abrasive; in either case the abrasive used is very fine, and the lap is thoroughly

lubricated. A number of laps may be necessary to finish either an internal or external thread to the required form and dimensions as illustrated in Figure 59. APPENDIX 4. SPECIFICATIONS FOR THREADING TOOLS

(RECOMMENDED PRACTICE)

The limiting sizes of the threaded product are always the essential requirements

of the manufacturer and user of threaded parts. To maintain these sizes, not

only the tools but also the processes employed must be suitable. So many varying factors are involved that it is not always possible to predetermine the exact

sizes Of the tools necessary to accomplish the required results. Variations in the nature of the material, the lubrication, the method of holding the product and

tool, the sharpness of the tool, etc., all have an effect on the final results.
FORM OF THREAD-CUTTING TOOLS 205

The effort has been made, in the following specifications, to establish sizes for various commonly used tools such that, when the tools are used with reasonable

care under normal conditions, a threaded product will be produced in conformity

with the product specifications.7 The commission is concerned primarily with

screw-thread products—that is, bolts, screws, and tapped holes—rather than

with threading tools or with methods of use. It should be understood, therefore, that any recommendations with reference to threading tools, or methods of use, are intended only as useful information and are in no way mandatory.

1. TOOLS FOR AMERICAN NATIONAL FORM OF THREAD (60°)

(a) FORM OF TOOLS FOR PRODUCING SCREWS

Screws or external threads are commonly produced by, lathe tools, solid or

adjustable dies, adjustable or opening die heads with removable chasers,thread

milling cutters, threading hobs, and roller dies. Of these, the dies, die-head chasers, and hobs are all multiple toothed, cutting

in several thread spaces simultaneously, and finishing the operation at one pass. Lathe tools are ordinarily single-pointed and operate in a single thread, which is finished by repeated passes; but multiple pointed chasers for use as lathe tools are sometimes made.

All rolled threads and many cut threads are produced with dies, chasers, or hobs made with master tools, such as hobs, taps, or milling cutters. These master

tools are frequently made with forming cutters or other tools, but the primary

tool is always made with a single-point tool. Angle and pitch errors tend to accumulate in a series of master tools and must be carefully considered in the

design and use of this single-point tool. The tables and charts given in this section apply only to the tool used to pro- duce the finished standard thread, and such a tool must be used on an axial section

of the work.

1. Inspection of Tooth Outlines.—All threading tools, whether for use in a lathe, die head, thread miller, or roller, and whether single or multiple pointed, must produce the proper tooth profile on an axial section of the work. In Figure

60, for instance, the lathe threading tool is shown tipped up to the helix angle of the thread to be cut. This is sometimes done for the sake of a better cutting

action, but necessitates a change in the tool shape, which must show an included

angle of less than 60°, when projected on line y—y of the illustration, if the

resulting thread as measured on the axial section x—x is to be exactly 60°. The

ordinary thread milling cutter, set at the helix angle, and roller dies must have

the same correction, if accurate results are desired. In brief,, the final test of accuracy in any threading tool is its ability to produce a thread of the proper

axial section as defined in the body of this report. Most cutting tools for standard threads have their Cutting edges in the axial plane of the work, so that the shape of those edges tends to reproduce itself on the screw thread. In forming and inspecting the cutting edges of these

tools, their forms may be directly compared with standard outlines. This can

be done by means of accurately formed templets, carefully applied under the

microscope. A more satisfactory and practical way is to draw the desired outline on a chart to a magnification of one hundred or two hundred times, and

then project on this chart the image of the cutting tool under inspection magnified to the corresponding degree. By this means the tool shape may be

quickly compared with the standard shape to a degree of accuracy much greater

than that required for commercial work. Care must be taken to use a lens

7 An analysis of the various factors which determine the accuracy of a screw thread in production is given

in Appendix 3, p. 198,
206 NATIONAL SCREW THREAD COMMISSION

Z

Fig. 60.

Effect on shape of tool or cutter of setting it at the helix angle

Fig. 61.

Shape for cutter or single point lathe tool not intended to trim crest of thread
FORM OF THREAD-CUTTING TOOLS 207

system free from distortion. Optical projection machines and comparators are

available for this work in commercial designs.

2. Outline for Single-Point Tool or Cutter.—In Figure 61 is shown

the form of outline, measured on an axial section of the work, required for a

single-point lathe tool or a milling cutter to produce directly a standard thread. Such a diagram, if drawn to a magnifi.cation of one hundred or two hundred

times, will serve as a chart for projection testing. Note the shaded area at the point of the tool, within which a tool point of any shape is permissible.

While sharp-cornered tools are easier to make, one with a permissible round

might be more durable.

3. Outline for Multiple-Tooth Chasers and Hobs.—In Figure 62 are given similar instructions for determining the outline of multiple-toothed chasers and hobs. The tolerance at the point or crest of the tool is the same as in Figure

61. At the roots of the teeth, however, the depth of the thread space is carried

far enough to clear the crests of the screw thread being cut. This is in accord- ance with modern practice in threading alloy steels, which tend to tear at the

crests. Relieving the chasers as shown minimizes this trouble.

It should be noted that this clearance at the crest of the screw is certain only on classes 2, 3, and 4 fits. If a class 1 screw is being cut to a minimum pitch

diameter from stock of maximum major diameter size, the crests will be trimmed

by the chaser. It is not possible to avoid this without carrying the grooves

in the chasers nearer to a sharp bottom than is desirable. When it is desired to follow the older practice which permits trimming of the crests, the outline shown in Figure 63 may be used. It is somewhat easier to make than the one shown in Figure 62. Note that the tolerance allowed on the shape of the points or crests is the same as in Figures 61 and 62. In both Figures 62 and 63 the shape of the bottom

to trim crest of thread
208 NATIONAL SCREW THREAD COMMISSION

of the thread spaces may be given any curved form which can be contained

within the shaded tolerance area and still produce screw threads which will agree with the standards set up in this report. In Table 98 are given the required dimensions for drawing the charts of Figures

61, 62, and 63 correctly for any standard pitch.

Table .

Dimensions for determining shape of cutter, chaser, hob, or tap teeth, American National coarse and fine threads

Threads

per inch, n

Pitch, V HXp HXp HtXp

Depth

of thread, h ViXh HXh H&Xh

Onehalf pitch diameter

toler- ance

for class 2

fit, MXT

10

72.

64_ 56.

48.

44.

40.

36.

32.

28.

24.

20.

18.

16.

14. 13.

12. 11.

10. 9..

8..

7_.

5... 4H4... 3^.

Inch

0. 01250

. 01389

. 01562

. 01786

.02083

.02273 .02500

. 02778

. 03125

. 03571

. 04167

.05000

. 05556

. 06250

. 07143

. 07692

. 08333

.09091 .10000

.11111 .12500

.14286

20000

22222

25000

28571

Inch Inch Inch

0. 00625 0. 00156 0. 00052

.001741 .00058

.001951 .00065

.00223 .00074

.00200 .00087

00781 01042

01136

01250

01389 01562 0178©

02083 02500

02778 03125

03571

04167 04545

05000

05556 06250

07143 08333

,10000

,11111 12500

,14286

.00284

,00312

,00347

,00391 ,00446

,00521 ,00625

,00694

,00781

,00962

,01042

, 01136

,01250

, 01389

, 01562

, 01786

, 02083

.02500

.02778

.03125

. 03571

00095

00104

00116

00130

00149 00174

00208

00231 00260 00298

00321

00347 00379

00417

,00463 00521

,00595

,00694

,00833 ,00926 01042

01190

Inch

0. 00812

.00902

. 01015

. 01160

. 01353

. 01476

.01624

. 01804

. 02030 .02320

. 02706

. 03248

04059

04639

04996

05413

05905

06495

07217 08119

09279

10825

12990

14434

16238 18558

Inch

0.00406

.00451 .00507

.00580

.00677

. 00738

.00812

. 00902

. 01015 .01160

. 01353

. 01624

.01804

. 02030

.02320

. 02498

. 02706

.02952

,04059

,04639

,05413

, 06495

, 07217

, 08119

, 09279

Inch

0. 00271

.00301 .00338

.00387

.00451 .00492

.00541

.00601 .00677 .00773

. 00902

.01083

. 01203

. 01353 .01546

. 01665

.01804 .01968

. 02165

. 02406

.02706

. 03093

04330

04811

05413

Inch

0. 00180

.00200 .00226

.00258

.00301 .00328

.00361

.00401 .00451

. 00515

.00601 .00722

.00802

.00902

. 01031 .01110

. 01203

. 01312

. 014.43 .01604

.01804 .02062

.02406

.02887

. 03208

Inch

0. 00135 .00150

.00193 .00226

.00246

.00271

.00301 .00338 .00387

.00451

.00541

.00601 .00677

.00773

,00902

,00984

,01083 01203

01353

,01546

,01804 02165

02406 02706

04124

Inch

0.00045 .00050

.00056

.00064

.00075

.00082

.00090 .00100

.00113 .00129

.00150

.00180

.00200

.00226 .00258

.00278

.00301 .00328

.00361

.00401 .00451 .00515

.00601 .00722

.00802

.00902

.01031

Inch

0.00085 .00090

.00095 .00100

.00110

.00115 .00120

.00125 .00135

.00155

.00165

. 00180

.00205

.00225 .00245 .00260

.00280

.00295 .00320

.00350

.00380

.00425

.00505 .00508

.00635 .00700

.00785

Inch

0. 00897 .00992 .01110

. 01260

. 01463

. 01591

. 01744

. 01929

. 02165

. 02475

. 02871 .03428

. 03813 .04284

.04884

. 05256

.06200

.06815 07567

09704

11330

13498

15069

19343

(b) TAPS

1. Tap Dimensions and Tolerances.—The dimensions and tolerances for cut and ground thread machine screw, hand, tapper, nut, and pulley taps given

in Tables 99 to 103, inclusive, were prepared with the cooperation of a com

mittee 8 of representative tap manufacturers and users, and represent present

practice for the production of tapped holes of the classes indicated below. These

standards may, therefore, be regarded as representing the best present commercial

practice. They should be regarded as suggestive only and in no way mandatory.

8 This committee, appointed in June, 1926, consisted of two members of the commission, two repre- sentatives of the Tap and Die Institute, one representative of the independent manufacturers of taps and dies, and two representatives of large users. The committee's report, as reprinted herewith, was

approved June 30, 1927.
TAP SPECIFICATIONS 209

The use, however, of taps that are in conformity with these tables should not be taken as a guarantee that the tapped holes produced thereby will necessarily

fall within any given class of fit. Figures 64 and 65 show the relations among

the maximum pitch diameters of the standard taps and the maximum pitch

diameters of the tapped holes for the four standard classes of fit. Taps may

cut oversize an amount depending on the cutting speed, condition of the tapping

machine, lubrication or cooling agent, relief and chamfer of tap, and other factors. In general, cut thread taps made to these specifications, when used under normal

conditions, should in the majority of cases produce holes within class 2, free-fit tolerances; ground thread taps, within class 3, medium-fit tolerances.

Fig. 63.Shape for teeth of chaser or hob intended

to trim crest of thread The general dimensions contained in these tables do not pertain to screw

threads, but are essential to the complete standardization of taps, and they

have for that reason been included. The point of measurement for the pitch diameter for all taps shall be at the

first full thread. The form of thread at the minor diameter is the American National form of thread, as specified in Section III, or sharper.

The maximum lead errors permitted are ±0.0030 inch in 1 inch of thread

for cut thread taps, and ±0.0005 inch in 1 inch of thread for ground thread

taps. All taps have center holes at both ends, with the exception that cut thread

taps up to and including five-sixteenths inch are pointed on the thread end. Clearance on a ground thread tap may be provided by a slight radial relief or a back taper of 0.0005 to 0.0010 inch per inch.
210 NATIONAL SCREW THREAD COMMISSION

Fig. 64.

Comparison of maximum pitch diameters of taps and nuts, American National coarse thread series

P/TCH • MCH

MAXIMUM P/TCH DIAMETERS OF TAPS

I -CUT THREAD MACHINE SCREW-TAPS Z-CUT THREAD HAND, NUT, AND TAPPER TAPS

i.- GROUND THREAD MACHINE SCREW TAPS

4- GROUND THREAD HAND. NUT,AND TAPPER TAPS

Fig. 65.

Comparison of maximum pitch diameters of taps and nuts, American National fine thread series
TAP SPECIFICATIONS 211

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212 NATIONAL SCREW THREAD COMMISSION

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TAP SPECIFICATIONS

to {£> oo «c g gg oooo oog ©°° 00 00 22 22 88 88 88 88 88 88 88 88 S3 3S

II Is IS II EE ££ §§ li IS SB

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214 NATIONAL SCREW THREAD COMMISSION

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12, 1512, 15

12, 1512, 15

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thread, cut thread -* a s g§ 2$ s§

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Sizes

and

threads

per

inch u ii U ii & ik U k ii
TAP SPECIFICATIONS

oooo or oo oooo oo oo 88 88 88 8 8

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0115 1.

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1375 1.1355 1.2630 1.2610 1.

5140 1.5120 1.7650 2.0155

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0070

1.0060 1.

1325 1.1310 1.

2580 1.2565 1.5090 1.5075 1.

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.

5625

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1.5000 1.

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1.1 .5676 .5902 .6866 .7107 .8050 .8305 .9212 .9555 .0347 .0729 .1597

.

1979

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216 national screw thread commission

1

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TAP SPECIFICATIONS 217

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TAP SPECIFICATIONS 219

2. Tolerances for Taps for Special Threads.—Tables of tolerances for two classes of taps for threads of special diameter and pitch are given, namely,

cut thread taps and ground thread taps. (See Tables 104 and 105.) The selection of the tap will depend upon the pitch diameter tolerance on

the tapped hole. A tap should be selected whose tolerance does not exceed

75 per cent of the pitch diameter tolerance on the tapped hole. Table 104.

Tolerances for cut thread taps, special diameters and pitches

Coarser pitches than American

National fine thread series Finer pitches than American National

fine thread series Major

diameter Pitch diameter Major

diameter Pitch diameter

From— ToMini- mum=

basic major

diameter

plus

Mini- mum=

minimum

pitch diameter

of hole plus

Tolerance, plus

Maxi- mum=

minimum

pitch diameter

of hole plus

Mini- mum=

basic major

diameter

plus

Mini- mum=

minimum

pitch diameter

of hole plus

Tolerance, plus

Maxi- mum=

minimum

pitch diameter

of hole plus

1 2 3 i 5 6 7 8 9 H

Me%m

H

H

Inch

0. 0030

.0040

.0055 .0070

Inch

0.0005

.0005 .0010 .0010

Inch

0.0020

.0025 .0030

.0035

Inch

0. 0025 .0030

.0040

.0045

Inch

0. 0020

.0025 .0025

.0035

Inch

0. 0005 .0005

.0005 .0010

Inch

0. 0015 .0020

.0025

.0030

Inch

0.0020

.0025 .0030 0040 m

m

m

22H

3

4

.0085 .0100

.0100 .0100

. 0015

.0015 .0020 .0020

.0040

.0045 .0050

.0055

.0055

.0060 .0070

.0075

.0035

.0045

.0045 .0055

.0010

.0010

.0010 .0010

.0030

.0035 .0035

. 0045

.0040

.0045

.0045

.0055 Note.—Maximum lead error =±0.003 inch in 1 inch of thread. Tolerance on half angle of thread

=

±40 minutes. Table 105.

Tolerances for ground thread taps, special diameters and pitches

Sizes

Coarser pitches than American

National fine thread series Finer pitches than American National

fine thread series

Major

diameter Pitch diameter Major

, diameter Pitch diameter

From— To—

Mini- mum=

basic major

diameter

plus

Mini- mum=

minimum

pitch diameter

of hole plus

Tolerance, plus

Maxi- mum=

minimum

pitch diameter

of hole plus

Mini- mum=

basic major

diameter

plus

Mini- mum=

minimum

pitch diameter

of hole plus

Tolerance, plus

Maxi- mum=

minimum

pitch diameter

of hole plus

2 3 i 5 6 7 8 9

H

Me

Viak

m

2H

H

H

lm

22H

3

4

Inch

0. 0025 .0030

.0035

.0040 .0050

.0065

.0080 .0080

.0080

Inch

0.0006

.0007

.0008 .0010

.0012

.0015 .0020

.0020 .0020

Inch

0. 0005

.0005

.0010

.0010 .0015 .0020

.0020 .0020

.0025

Inch

0. 0011 .0012

.0018

.0020

.0027

.0035 .0040

.0040

.0045

Inch

0. 0015 .0020

.0020

.0025

.0025 .0030

.0030

.0035

.0035

Inch

0.0005

.0005

.0006 .0007

.0008

.0010

.0010

.0015

.0015

Inch

0.0005

.0005 .0008

.0008 .0010

.0015

. 0015

.0015 .0020

Inch

0. 0010 .0010

.0014

.0015 .0018

.0025 .0025

. 0030

.0035 Note.—Maximum lead error =±0.0005 inch in 1 inch of thread. Tolerance of half angle of thread

=

±20 minutes. 18415°—29 15
220 NATIONAL SCREW THREAD COMMISSION

3. Shape of Cutting Edge for Taps (and Other Internal Threading

Tools).—In Figure 66 is shown the form of outline, measured on an axial section

of the work, required for a tap or other internal threading tool intended for cutting threads of American National form. These outlines are alike for all pitches and

classes of fit. Such a diagram, if drawn to a magnification of one hundred or two

hundred times, will serve as a chart for projection testing. Note the shaded area

at the point of the tool, within which a tool point of any shape is permissible. Also note the shaded area at the root of the thread which shows permissible variations in tooth outline at this point.

While sharp-cornered tools are easier to make, one with a permissible round

at the point might be more durable. In any event, the maker of the tap or other

tool should keep the outline well away from the lower part of the permissible

area, represented by the basic flat of KXp. The danger here is that after a few holes have been tapped the corners will be rounded over so that the tapped

hole rejects the "go" gage. Tables 98 to 103, inclusive, give the necessary dimensions for drawing the diagram shown in Figure 66 for any standard pitch.

4. Marking of Taps.—It is recommended that taps be marked to indicate the diameter, pitch, and thread series or thread form, as, for example (see Section

II, division 2, "Symbols"):

A 1-inch, 8-pitch cut thread tap will be marked l"-8-NC.

A 1-inch, 14-pitch ground thread tap will be marked 1"-14-NF-G.

A 1-inch tap, 16 threads per inch, American National form of thread, will be marked 1"-16-NS.

A 1-inch tap, 16 threads per inch, left hand, American National

form of thread, will be marked . 1"-1GL.H.-NS

for shafie of Jbo/nT

J>

Fig. 66.

Shape for teeth of top or internal thread-chasing tool
DIE-HEAD CHASERS 221

A multiple threaded tap will be marked as above, and also with

the number of starts. Where the size of the shank is large

^enough, the lead should also be given. Thus a double- threaded tap, 1 inch in diameter, 16 threads per inch, American

National form of thread, with a lead of 0.125 inch will be

marked 1"-16-NSDouble,Lead-

\ 0.125.

(c) DIE-HEAD CHASERS

There are given in Table 106 the simplified list of sizes and varieties, for threads

of American National form, of die-head chasers for self-opening and adjustable

die heads, as adopted December 4, 1925, at a general conference of representative

manufacturers, distributors, and users, and promulgated in United States Department of Commerce Simplified Practice Recommendation No. 51. Table 106.

Die-head chasers, stock sizes for threads of American National form

Sizes i

Threads per inch

Sizes 1

Threads per inch

American

National

coarse thread

seiies

American

National

fine thread

series

Fine

threads

for lighting-fix- ture tubing

American

National

12-pitch thread

series (railwaysizes)

American

National

coarse thread

series

American

National

fine thread

series

Fine

threads

for lighting-fix- ture tubing

American

National

12-pitch thread

series (railway

sizes)

1 2 3 4 5 1 2 3 4 5

5. 40

3232

24

2420

18

1614

1312

11

K 9 3 14(18) 27 12

1212

12

1212

12

12

12

1212

G8 36

32

28

28

24

2420

20

1818

1 8 14 27 10 lMe

12 m 7 12 H 2727

2727

2727

27

1Mb Mo m 7 12 % lMe Ms m

H - 121212

12

12

12

1H 6

54^2

12 m

H - 2 »M« % 10 16

2 (24) 27

1 Although self-opening die heads have a diameter adjustment, all chasers not stamped with these sizes will be regarded as specials.

2 Spark plug bushing, U inch—24.

a Spark plug shell, % inch—18. (d) TAP-DRILL SIZES

(Classes 1 to 4, inclusive) The essential requirement of a tap drill is that the hole produced by it shall be such that, when tapped with a screw thread, the minor diameter of the tapped

hole shall be within the specified limits shown in Tables 7 to 14, inclusive, of Section III. It should be noted that the minor diameters of the tapped holes

are the same for classes 1 to 4, inclusive. This condition results from the re- quirement on page 18, Section III, with reference to clearance on minor diameter:

"4. Clearance on Minor Diameter.—A clearance shall be provided at the minor diameter of the nut by removing from the crest of the basic thread form an amount such as to provide a depth of thread equal to not less than

62 to 75 per cent (depending on the size), and not more than 83}i per cent

of the basic thread depth. (See fig. 17.) "

If the drill is too large, the minor diameter of the tapped hole will also be too

large and the thread in the nut will be too shallow; that is, too small a percent-
222 NATIONAL SCREW THREAD COMMISSION

age of a full thread. As an extreme case the threads in the nut will engage only

the tops of the threads on a bolt of correct size, and under stress the threads of the screw will strip and the full strength of the fastening will not be developed.

If, on the other hand, the tap drill is too small, the tap will be forced to cut a thread of full depth, and in the extreme case to act as a reamer also. This will result in excessive power consumption and tap breakage, and will also make the minor diameter of the tapped hole dependent upon the minor diameter of the

tap. This is undesirable, since the minor diameter of the tap is not, in general, held to the same close limits as the other tap elements, and as a result the minor

diameter of a hole tapped under these conditions may be in error even though the tap is otherwise correct. It is a well-known fact that the size of the hole produced by a tap drill depends

to some extent upon the method of grinding the drill, the material drilled, the

lubricant used, and the speed and feed of operation. This being true, it is ap- parent that fixing the diameter of the tap drill does not completely fix the diameter of the drilled hole. The most that can be accomplished is to fix the drill diameters between certain limits and to depend upon correct grinding, lubri- cation, and operation to keep the diameter of the holes within prescribed limits. There are given in Tables 107, 108, and 109 all drills regularly carried in stock, both English and metric, which fall between the limiting dimensions of the minor diameter of the threaded hole for the American National coarse, fine, and

12-pitch thread series. A drill near the larger limits may be selected when it is desired to minimize tapping difficulties or provide for considerable wear of the

drill; thus the drill may be allowed to wear undersize until the holes produced

reach the lower limit on minor diameter, but the unworn drill can be allowed

to cut only a very small amount oversize. On the other hand, a drill near the

smaller limit may be selected when conditions of lubrication, operation, physical

properties of material, etc., cause the drill to cut oversize, but such selection permits less wear of the drill. Table 107.

Sizes of tap drills, American National coarse-thread series Minor diameter of nut Stock drills within limits on minor diameter of nut

Size of thread Threads

per

inch

Numbered and fractional inch sizes Metric sizes

Basic Maxi- mum

Mini- mum

Nominal size Diameter

Per

cent of depth

of basic thread

Nominal

size Diameter

Per

cent of depth

of basic thread

1 2 3 4 5 6 7 8 9 10 11

1- 64 Inch

0. 0527 Inch

0.0604 Inch

0.0561 No. 53 Inch

0. 0595 67 mm1.5 Inch

0. 0591 .066968 [No. 51 .0670 82

69

1.7 82 9 56 .0628 .0715 .0667 INo. 50 .0700 L 75 .0689 74

1.8 .0709 65

48 .0719 .0764

( 5Ai inch iNo. 47. .0781

. 0785

7776 2.0 .0787 75

3 .0820 INo. 46 .0810

.0820

67 iNo. 45 63 (No. 44 .0860

.0890

80 2.2 .0866

.0886

78

4. 40 .0795 .0913 0849 jNo. 43 71 2. 25 72

2.3 .0906 66

5... 40 .0925 .1043 .0979 fNo. 40

J No. 39 .0980

.0995

83

79 2.52.6 .0984 .1024

82

70 INo. 38- . 1015 72 No. 37 . 1040 65
TAP-DBILL SIZES 223

Table 107.

Sizes of tap drills, American National coarse-thread series—Contd.

Size of thread Threads

per

inch

Minor diameter of nut

Basic Maxi- mum

Mini- mum

Stock drills within limits on minor diameter of nut Numbered and fractional inch sizes

Nominal size Diameter

Per

cent of depth

of basic thread

Metric sizes

Nominal

size

32

32

20

Inches

0. 0974

.1234

.1359

.1619

.1850

.2403

.2938

.3447

.4001 .4542

.5069

.6201 .7307

.8376

.9394

1. 0644

1. 2835

1. 4902

1. 7113

1. 9613

2. 1752

2. 4252

2. 6752

2. 6288

Inches

0. 1118

.1378

.1541

.1801

.2060

. 2630

.3184

.3721

4290

4850

5397

6553

1. 1108

1. 3376

1. 5551

1. 7835

2. 0335

2. 2564

2. 5064

2. 7564

2. 7216

Inches

0. 1042

.1302

.1449

.1709

.1959

.2524

.3073

.3602

4167

4723 5266

6417

7547

. 8795 . 8647

.9704

1. 0954

1. 3196

1. 5335

1. 7594

2.0094

2. 2294

2. 4794

2. 7294

2. 6907

No. 36—

%4 inch. No. 35... No. 34... No. 29.

Inches

0. 1065 .1094 .1100

. 1110 .1360 No. 26. No. 25. No. 24- No. 23.

l Hi inch. No. 17-.. No. 16.... No. 15.... No. 9 No. 8 No. 7

J %4 inch. No. 6 No. 5

Ha inch. 0._

1470

1495

1520 1540

1719

1730

1770

1800 1960

1990 2010

2031 2040

2055 2570

2610

,3125 ,3160 3680

2%4 inch .4219 78

3 lM inch .4844 72

17/s2 inch . 5312 79 inch .7656 76 % inch .8750 77

6 %4 inch .9844 76 V/ii inches.. 1. 1094 76

1

2 }^4 inches . 1. 3281 79

|1

3 %4 inches. 1.5469 78

fl 4 %4 inches . 1. 7656 81

\l 25/i2 inches

-

1. 7812 76 (2^4 inches.

-

2. 0156 81 \2H2 inches.. 2. 0312 76 /2!%4 inches. 2. 2344 82 \2H inhces... 2. 2500 77

(231/s4 inches

.

2. 4844 82

XlYi inches... 2. 5000 77

f24 %4 inches. 2. 7344 82 [2H inches..

.

2. 7500 77

/24 %4 inches. 2. 7031 80 \22%2 inches. 2. 7188 76

mm

2.7

2.75

2.8

3.4

3.5

3.7

3. 75 3.8

4.4

4.5

5.0

5. 1 5.2

7.9 8.0

9.2

9. 25 9.3

9.4

12.0

13.5

16.5 19.5 22.0

25.0

28.0

39.0

39.5

45.0

67.0

63.0

63.5

69.5 70.0
224 NATIONAL SCREW THREAD COMMISSION

Table 108.Sizes of tap drills, American National fine-thread series

Size of thread Threads

per inch

Minor diameter of nut

Basic

Inches

0. 0438 .0550

.0657

.0758

.0955

.1055

.1279

.1494

.1696

.2036

.2584

.3209

,3725

4350

4903 5528

.7822

.9072

1. 0167

1. 1417

1. 3917

1. 6201

1. 8701

2. 0876

2. 3376

2. 5876

2. 8376

Maxi- mum

Inches

0. 0492 .0610

.0724

.0834

.0937

.1049

.1158

.1391

.1618

.1833

.2173

.2739

.3364

.3906

.4.531 .5100

.5725

.8062

.9312

1. 0438

1. 1688

1. 4188

1. 6525

1. 9025

2. 1282

2. 3782

2. 6282 2.8/82

Mini- mum

Inches

0.0465 .0580

.0691 .0797

.0894

.1004

.1109

.1339

.1562

.1773

.2113

.2647

.3299

.3834

. 5024 .5649

.6823 .7977

.9227

1. 0348

1. 1598 1.4098

1. 6417

1. 8917

2. 1147

2. 3647

2. 6147

2. 8647

Stock drills within limits on minor diameter of nut Numbered and fractional inch sizes

Nominal size

No. 56.. jHUinch. No. 53. No. 50. No. 46. No. 45. H2 inch. No. 42. _ No. 38. No. 37. No. 34. No. 33. No. 29.

No. 3.

W

inch. 2%4 inch...

J H6 inch.

0)

0)

0)2H inches.. 2H inches..

2?4 inches..

2

7A inches..

Diameter

Inches

0. 0465

.0595

.0700 0810

0820

1015 1O10

1110

1130 1360

1562

1570

1590

1610 1800

1820

2130

,2720

,3320

,3860

,3906

4531 5062

. 6875 P)

0)(0

2. 1250

2. 3750

2. 6250

2. 8750

Per

cent of depth

of basic thread

78

0)

Metric sizes

Nominal

size

mm

1.2 1.25

1.5

1.8

2.1

2.3

3.4

3.5 4.0

4.1

5.4

5.5

8.4 8.5

14.5 17.5

0) 23.5

26.5

29.5 36.0 0)

0)

54.0

66.5 73.0

Diameter

Inches

0. 0472

.0492

.0709

.0827

1024

1142

1339 1378

1575

1614

1811

2126

2165

,2677

,2717 ,3307 3346 .3839 .3858

4528

.5709 .6890 0)

.9252

1.0433 L 1614 L 4173 V)

03

2. 1260

2. 6181 2.8740

» No standard size.
FIRE-HOSE RETHREADING TOOLS 225

Table 109.

Sizes of tap drills, American National 12-pitch thread series

of thread Threads

per inch

Minor diameter of nut

Basic Maxi- mum

Mini- mum

Stock drills within limits on minor diameter of nut Numbered and fi actional inch sizes

Nominal size Diameter

Per

cent of depth

of basic thread

Metric sizes

Nominal

size Diameter

Inches

0. 3917 .4542

.5167 .5792

.6417 .7042

.7667 .8292

.8917 .9542

1. 0167

1. 0792

1. 1417 1.2042

1. 2667

1. 3917

1. 6417

1. 8917

2. 1417

2. 3917

2. 6417

2. 8917

Inches

0. 4221 .4850

.5438

.7313 .7938

.8563

.9188

.9813

1.0438

1. 1063

1. 1688

1. 2313 % 2938

1. 4188

1. 6688

1. 9188

2. 1688

2. 4188

2. 6688

2. 9188

Inches 0.4098

.4723

.5348

.5973

.7223

.7848

.8473

.9098 .9723

1. 0348

1. 0973

1. 1598

1. 2223

1.2848

1. 4098

1. 6598

1.9098

2. 1598

2. 4098

2. 6598

2. 9098

,2%4'inch"

3 Yei inch.

(i) 0)

0) —

Inch

0. 4130 80

.4219 72 .4844 72

0) 0)

0) 0)

0) 0)

mm

10.5 Inches

0. 4134

12.0

0)

0)0)

18.5 20.0

(!) 0)

0)26.5 28.0

29.5

0)0)36.0

0)

0)55.0

(») w

74.0

.4724

0)

0)

0)

.7283 .7874

0)0)

0)

1. 0433

1. 1024

1. 1614 0)

GJ

1. 4173

0)0)

2. 1654 0)0)

2. 9134

1 No standard size.

2. RETHREADING TOOLS FOR AMERICAN NATIONAL FIRE-HOSE

THREADS

In the interest of the universal adoption of the American National fire-hose threads throughout the United States, attention is directed to the fact that sets

of tools for rethreading existing hydrants and hose couplings are commercially

available. Such sets comprise roughing and finishing taps, roughing and finish- ing dies, expanders for expanding undersize externally threaded fittings preparatory to rethreading, gages, and various accessories. The tools are applicable

where existing threaded fittings do not differ so widely from the American

National standards as to leave insufficient stock for the new thread. By the

use of such tools a considerable number of municipalities have at small expense

converted their existing equipment, and thus availed themselves of the important

advantages which standardization affords.

3. TOOLS FOR AMERICAN NATIONAL PIPE THREADS (60°)

(a) TAPS

, "Recommended dimensions of standard taps for American National taper pipe

threads are given in Table 110.

.
226 NATIONAL SCREW THREAD COMMISSION

Table 110.

Dimensions of standard taps for American National taper pipe

threads

Length over

Nominal Toler- ance

Length of thread

Nominal Toler- ance

Diameter of shank

Nominal (maxi- mum)

Toler- ance

Size of square

Nominal (maxi- mum)

Toler- ance

Projection of small end

through taper gage

Nominal

Inches 2^6

314

4m

m

m6

3A

Inch

±1/32 ±^2

±Me

±M6

±H6

±He

±Ha

±Hb

±Me

Inches U

lHe

lHe Wi

1%

1%

Wi

13/4 m

2H

2iMe 2%

Inch ±3/6 4 ±%4

±%4

±%4

±3

/<54 ±%4

±%4

±%4

±3/64

Inches

0. 4375 .5625 .7000

.8650

1. 0750

1. 1250

1. 3125

1. 5000

1. 8750

2.2500

2. 6250

2.8125 3.0000

Inch

-0. 007 -.007

-.007

-.007

-.009

-.009 -.009

-.009

009

Inches

0. 328

.421

.531 .640 .812

.984

1. 125

1. 406

1. 687

1. 968

2. 108

2. 250

Inch -0.006 -.006

-.006

-.006

-. 010 -.010

-. 010 -. 010 -.010

-.010

-.010 -.010

-.010

Inch

0. 312

.459 .454

.579

.565 .678

.925

.925

.938 .950

(b) DIE-HEAD CHASERS

There is given in Table 111 the simplified list of sizes and varieties, for American National straight and taper pipe threads, of die-head chasers for self-opening

and adjustable die heads, as adopted December 4, 1925, at a general conference

of representative manufacturers, distributers, and users, and promulgated in United States Department of Commerce Simplified Practice Recommendation

No. 51. Table 111.

Die-head chasers, stock sizes for American National straight and

taper pipe threads

Size Threads per inch Size Threads per

inch

1 % 2

VsH

H

V2%

27

18

18

1414

1IK

22>A

11H uy2 8

(c) TAP DRILL SIZES

Sizes of tap drills recommended for American National taper pipe threads are given in Table 112.

Sizes of tap drills recommended for American National straight pipe threads

are given in Table 113.
Table 112 PIPE-THREADING TOOLS 227

.

Sizes of tap drills, American National taper pipe threads

Nominal sizes, in inches Threads

per inch

Minor

diameter

at small end of pipe Tap drill Nominal sizes, in inches Threads

per inch

Minor

diameter

at small end of pipe Tap drill

3 3 4 I 2 3 4 H —

-

27

1818

14

141H/2 im

Inches

0. 33388

. 43294

. 56757

. 70129

. 91054

1. 14407

1. 48757

1. 72652

Inches

2

J/64 7A*Me

45/64

2 %2

1%4

I*J*S

1

2 %2

2.... im

8

88

88

8

8

Inches

2. 19946

2. 61953

3. 24063

3. 73750

4. 23438

4. 73125

5. 29073

6. 34609

Jjichcs 2H6 2H

334

414 4%

5%2

6*J*a

n 2H % 3

Yi 3H n 4

i 41/2 m 5 m 6 Table 113.

Sizes of tap drills, American National straight pipe threads

Nominal sizes, in inches Threads

per inch Minor

diameter,

basic Tap drill Nominal sizes, in inches Threads

per inch Minor

diameter,

basic Tap drill

2 3 4 2 3 4 U 27

18

18

1414

11 J4 im

ny2

Inches

0. 34513

. 44544

. 58257

. 72129

. 93172

1. 16907

1. 51382

1. 75277

Inches3%4 2%2 15/16

l

5/32 13%4 in

2.-

88

88

8

8

8

Inches

2. 22671

2'. 66216

3. 28850

3. 78881

4. 28713

4. 78594

5. 34929

6. 40597

Inches 2%2

221^2 3%2

32H2

49/32 42542

51 H2

61%2

H 2H % 3 H - H - 4

l 4H W— 5 m— 6.

4. TOOLS FOR AMERICAN NATIONAL ACME SCREW THREADS

The methods of producing Acme threads are subject to greater limitations than those for fastening screws on account of the larger amount of metal to be removed, the small thread angle, and the usually larger helix angles, the last two being conducive to side-cutting. Further limiting conditions are the necessity for accurate control of the minor diameter of the screw and for rounding or beveling the corners at the minor diameter of the nut. Consequently the matters

of clearances on cutting tools and of proper tooth outlines require careful consideration. The tool specifications here given are intended as an aid in meeting the specifi- cations laid down for the threaded product, and in practical application may be

modified as variations in the nature of the material threaded, the lubrication, the methods involved, and other varying factors may require; the essential requirement being that the specified limiting dimensions of the threaded product be

maintained.

(a) FORM OF TOOLS FOR PRODUCING SCREW

All threading tools, whether for use in a lathe, die head, or thread miller, and

whether single or multiple pointed, must produce the standard 29° thread profile on an axial section of the work when the helix angle is less than 5°. Most cutting

tools for standard 60° fastening screw threads have their cutting edges in an axial plane of the work, and the shape of those edges is practically reproduced on the work for the reason that the helix angle of a 60° thread is seldom over 5°, In
228 NATIONAL SCREW THREAD COMMISSION

producing Acme threads, however, particularly if the helix angle is larger than 5°,

it is necessary that the tool be set at an angle corresponding to the helix angle

of the thread at a diameter less than the diameter at the pitch line. This necessi- tates a modification of the tool shape, such that its included angle is less than

29°, in order to produce in the work a thread angle of 29° in an axial plane. On

threads having a small thread angle, such as Acme threads, a distortion of the thread profile becomes pronounced when the helix angle is large, and which is greater at the minor diameter of the screw than at the major diameter because

of the greater rate of increase of the helix angle as the center of the work is approached. In order to reduce such distortion to a minimum, when the helix angle at the minor diameter is greater than 5°, the tool should be set at an angle

corresponding to the helix angle at a diameter less than the diameter at the pitch

line.In Figure 67 is shown, for example, the modification of shape required for a

single-point lathe tool to be set to a helix angle s. The tool has an included angle 2 a', which is less than 29°, a radial clearance V, and a side clearances'.

Fig. 67.

Clearances for single point cutting tool s=helix angle of screw.

a

=

half angle of thread. Tan F=tan s cot a. Tan a'=tan a sec. V. h'=h cos V. Tan s'=tan s cos V.

1. Outline for Single-Point Tool or Cutter.—In Figure 68 is shown the form of outline required for a single-point lathe tool or a milling cutter to produce

directly a standard thread. Such a diagram, if drawn to a magnification of 50

or 100 diameters, will serve as a chart for projection testing. The shaded area

at the point shows the permissible variation in outline at this point, but straight- ness of the cutting edge of the point, except for rounding at the corners, should be maintained.

2. Outline for Multiple-Tooth Chasers and Hobs.—In Figure 69 is shown a similar outline for multiple-toothed chasers or hobs. The tolerance at the point or crest of the tool is the same as in Figure 68. At the roots of the

teeth, however, the depth of the thread space is carried far enough to clear the
TOOL FORMS FOR ACME SCREW THREADS 229

JS£eCoL .9. TABLEU4- ph$pe ofpoint

Fig. 68.

Shape for cutter or single point lathe tool, Acme threads Note.—In cutting screws of classes 2, 3, or 4 Acme, with the permissible variation in width of point here shown, only a part of the thread thickness tolerance can be used when the width is a minimum, and all or most of it must be used when the width is a maximum, in order to produce the minor diameter of the screw

within the specified limits.

Rootmay have

7s//

:

Fig. 69.

Shape for teeth of chaser or hob Note.—In cutting screws of classes 2, 3, or 4 Acme, with the permissible variation in width of point here shown, only a part of the thread thickness tolerance can be used when the width is a minimum, and all or most of it must be used when the width is a maximum, in order to produce the minor diameter of the screw

within the specified limits.
230 NATIONAL SCEEW THREAD COMMISSION

crests of the screw thread being cut. This is necessary, as it is practically impossible to trim the crests with the chaser or hob and maintain the tolerances on major and minor diameters and thread thickness, particularly when producing

screws of classes 2, 3, or 4 fits. The shaded area at the point shows the permissible

variation in outline at this point, but the straightness of the cutting edge of the

point, except for rounding at the corners, should be maintained. In Table 114 are given the required dimensions for drawing the charts of Figures 68 and 69.

(b) TAPS

1. Tap Dimensions.—Tap dimensions are given in Table 115, which are suit- able for taps intended for producing Acme threads to specifications for classes 1, 2, 3, or 4, the nut dimensions of Acme threads being the same for all classes of

fit with the exception of the maximum minor diameter. The values tabulated Shadedarea z>how& tolerance for ^hape of pp/nt

minimum

i offi/Zete ar

diameter

/e i/s, co/. //

Fig. 70.Shape for teeth of tap or internal thread chasing tool, Acme

threads

for the maximum minor diameter of the tap correspond to the maximum minor

diameter of the nut, classes 2, 3, or 4 Acme. As it is necessary for the tap to produce a radius or bevel at the minor diameter of the nut at the corners of the

thread, this radius is also tabulated, and in order to insure that such a radius or

bevel will be produced, the minimum minor diameter of the tap is also specified.

This is taken to correspond to the maximum minor diameter of the screw,

classes 2, 3, or 4 Acme.

2. Design of Taps.—On account of the large amount of metal to be removed

in tapping an Acme thread, at least two taps are required, a roughing tap and a

finishing tap. In fact, a common practice has been to furnish Acme thread taps

in sets containing from two to five taps to produce a thread of a given size, but if properly designed and made, two taps should be sufficient except when the nut

to be tapped is unusually long.
TAPS FOR ACME SCREW THREADS 231

Spiral flutes are an essential feature of a properly designed Acme thread tap, the helix angle of which is such that the cutting faces are at 90° to the helix of the

thread. Chip clearances on both the top and sides of the thread are also neces- sary for satisfactory cutting action. The roughing tap is so made that the thread space cut is narrow, leaving suffi- cient metal to be removed by the finishing tap to assure efficient action of the

latter, and that the major diameter be slightly small. The finishing tap is provided

with a leader section having threads of the same thickness as the roughing tap.

> Behind the leader section the thickness of the threads gradually increases at such

a rate as to cause the tap to produce chips of thicknesses which will assure good

cutting action. Behind this second section the thread profile of the straight

portion of the tap is such as to produce threads in the nut within the specified tolerances—that is, as specified below under "shape of cutting edge." The

finishing tap is preferably a ground-thread tap, especially when a smooth finish

is desired.

3. Shape op Cutting Edge for Finishing Taps (and Other Internal

Threading Tools).—In Figure 70 is shown the form of outline, measured in an

axial section of the work, required for a tap or other internal threading tool in- tended for cutting threads of Acme form. These outlines are alike for all classes

of fit. Such a diagram, if drawn to a magnification of 50 or 100 diameters, will serve as a chart for projection testing. The shaded areas in Figure 70 at the major

and minor diameters show the permissible variations in tooth outlines at these

points; the fillets at the minor diameter and straightness of the cutting edge on

the minor diameter should be maintained.

Table 114.

Dimensions for determining shape of cutter, chaser, or hob teeth, American National Acme threads

Number of threads per inch Pitch, p

Basic width

of flat, 0.37069p

Width of point of single-point

tool, chaser, or hob, all fits (see figs. 68 and 69)

Mini- mum

Toler- Maxiance mum

m.

2... 2H

3... 4...

5...

6...

8...

10..

12..

Inch

1. 00000

. 75000

. 66667 .50000

. 40000

. 33333 .25000 .20000

. 16667

. 12500 .10000

. 08333

Inch

0. 50000

. 37500

. 33333 .25000

. 20000

. 16667

. 12500

. 10000

. 08333

. 06250 .05000

. 04167

Inch

0. 33333

. 25000

. 22222

. 16667

. 13333

. 11111

. 08333

. 06667

. 05556

. 04167

.03333

. 02778

Inch

0. 250C0

. 18750

. 16667 .12500

. 10000

. 08333

. 06250

. 05000

.04167

.03125

. 02500

. 02083

Inch

0. 37069

. 27802

. 24713

. 18534

. 14828

. 12356

. 09267

. 07414

. 06178

. 04634

. 03707

Inch

0. 3707 .2780

. 2471 .1853 .1483

. 1236 .0927

.0741 .0618

.0463

.0371

. 0309

Inch

0. 0040

.0034

.0032

.0028 .0025

.0023 .0020

.0018 .0016

.0014 .0012

.0011

Inch

0. 3747

.2814 .2503

.1881

. 1508

. 1259 .0947 .0759

.0634 .0477

. 0383

. 0320
232 NATIONAL SCREW THREAD COMMISSION

Table 115.

Dimensions and tolerances for taps for American National Acme

screw threads

Number of tb rebels per inch

Major diameter Width of thread space

at basic pitch line Minor diameter Radius

of fillet at minor

diameter, mini- mum

Depth

of thresd

mini- mum

Mini- mum

equals

basic major

diameter plus

Tolerance, plus

Maxi- mum

equals

basic major

diameter plus

Maxi- mum

Tolerance, minus

Mini- mum

Maxi- mum

equals

basic major

diameter minus

Tolerance, minus

Mini- mum

equals

basic major

diameter minus

1 3 1

_ g g 9 10 11 12

Inch Inch Inch Inch Inch Inch Inch Inch Inch Inch Inch

1 0. 020 0. 048 0. 068 0. 4980 0. 0040 4940 9900 0. 0150 L 0050 0. 02 0. 5100

1X4 i020 !o40 !060 !3733 !(X)34 !3699 [7413 !0130 ^7543 .02 .3850 iy2 .020 .037 .057 .3317 .0032 .3285 .6.585 .0123 .6708 .02 . 3433

2 .020 .030 .050 .2486 .0028 .2158 .4929 .0106 .5035 .02 .2600 .020 .026 .046 .1988 .0025 .1963 .3937 .0095 .4032 .02 .2100 .020 .023 .043 .1655 .0023 . 1632 .3275 .0087 .3362 .01 .1767 .020 .020 .040 . 1240 .0020 . 1220 .2450 .0075 .2525 .01 .13.50 6 .020 .017 .037 .0991 .0018 .0973 . 1955 .0067 .2022 .01 .1100

6 .020 .015 .035 .0825 .0016 .0809 .1626 .0061 .1687 .01 .0933 8 .020 .013 .033 .0618 .0014 .0604 .1215 .0053 . 1268 .01 .0725 10 .020 .011 .031 .0494 .0012 .04S2 .0968 .0048 .1016 .01 .0600 12 .020 .010 .030 .0411 .0011 .0400 .0804 .0044 .0848 .01 .0517 APPENDIX 5. CLASS 5, WRENCH FIT FOR THREADED

STUDS (TENTATIVE SPECIFICATIONS)

The tentative specifications embodied herein for class 5, wrench fit for threaded

studs, are based partly upon experimental data obtained in an investigation

conducted by the Bureau of Standards and partly upon data obtained from manufacturers relative to existing practice. The specifications are complete only for studs set in hard materials (cast iron, steel, bronze, etc.), and are not complete

for studs set in aluminum for which larger interference of metal is permissible.

They are presented for the information of those who may have use for them but

are in no way mandatory.

1. FORM OF THREAD

The American National form of thread profile, as specified in Section III, shall be used. The thread form of the tapped hole is modified, however, by truncating

the crest of the thread a greater amount than that specified for threads of strictly

American National form. This truncation is such that the minimum depth of thread engagement is one-half of the basic thread depth. The maximum depth

of engagement is governed by the tolerances specified for the major diameter of the stud and the minor diameter of the tapped hole.

2. THREAD SERIES

The range of sizes from 34 inch to 13^ inches, inclusive, of the American

National coarse-thread series and the American National fine-thread series of

sizes and pitches, as given in Section III, are recommended for general use for

class 5, wrench fit for threaded studs.
WRENCH FIT FOR THREADED STUDS 233

3. CLASSIFICATION AND TOLERANCES

The accompanying specifications are intended for use in the production and

assembly of threaded studs and tapped holes on an interchangeable basis.

(a) GENERAL SPECIFICATIONS The following general specifications apply for all materials to class 5, wrench

fit for threaded studs, American National coarse-thread series and American

National fine-thread series.

1. Definition.—The wrench fit class is intended to cover the manufacture

of threaded studs and holes which are to be assembled permanently by the

application of power.

2. Minimum Tapped Hole.—The pitch diameter of the minimum threaded

hole corresponds to the basic size, the tolerances being applied above the basic

size.3. Maximum and Minimum Stud Above Basic.—The pitch diameter of both

the maximum and minimum studs of a given size and pitch are above the basic dimensions, which are computed from the basic major diameter of the thread. The maximum major diameter of the stud is basic.

4. Length of Engagement.—A length of engagement equal to one and onehalf times the basic major diameter for studs set in hard materials, and two times

the basic major diameter for studs set in soft materials, is the basis of the toler- ances and allowances specified herein. The length of engagement of two diameters is especially desirable for studs set in soft materials when subject to alter- nating stresses or to vibration.

5. Minimum Interferences.—The minimum interferences specified are such

that a wrench-tight fit will result in all cases. If the thread surfaces are smooth

and thread form is maintained, these interferences will permit disassembly and

reassembly of the same stud and hole as many as four times and still produce a satisfactory wrench-tight fit. 6. Maximum Interferences.—The maximum interferences specified are such

that all conditions necessary for a good wrench fit are fulfilled. If threads are

well lubricated with a suitable lute no galling or seizing of the threads will result. Also, mild-steel studs, even of the smaller sizes, will not break if the rate of as- sembly is not excessive. When a mixture of white lead and oil is used as a lute it is important that it be of a thick fluid consistency in order to prevent galling or seizing, particularly

when fine threads in hard materials are concerned, and that it be applied liberally.

If a lute consisting of 40 per cent zinc dust, which has passed through a 200-mesh

sieve, and 60 per cent petrolatum is used, the tendency for the threads to gall or seize with maximum interference is materially reduced.

7. Tolerances.—(a) The tolerances specified represent the extreme variations permitted on the product.

(6) The tolerance on the tapped hole is plus, and is applied from the basic

size to above basic size.

(c) The tolerance on the screw is minus, and is applied from the maximum

screw size to below the maximum screw size.

(d) The pitch diameter tolerances for the tapped hole are the same as for the

class 4, close-fit nut, except on the ^-inch size, as noted in Table 116. These

tolerances necessitate the use of ground-thread taps.

(e) The pitch diameter tolerances for the stud are as given in Table 116. They

are the maximum variations permissible for each individual size of stud, as determined by the maximum and minimum interferences.

(J) Pitch diameter tolerances include angle variations but do not include lead

variations.
234 NATIONAL SCREW THREAD COMMISSION

(g) The tolerances on the major diameters of class 5, wrench-fit studs are the same as for class 2, free-fit finished screws.

(h) The minimum minor diameter of a stud of a given pitch is such as to result in a basic flat (YsXp) at the root. It is equal to the measured pitch diameter of the stud minus the basic thread depth.

(i) The maximum minor diameter of a screw of a given pitch may be such as

results from the use of a worn or rounded threading tool, when the pitch diameter

is at its maximum value. In no case, however, should the form of the thread, as results from tool wear, be such as to cause the screw to be rejected on the maximum minor diameter by a "go" ring gage, the minor diameter of which

is equal to the minimum minor diameter of the nut.

Fig. 71.Illustration of tolerances, allowance, and crest clearances for class 5, wrench fit for threaded studs

(j) The maximum major diameter of the tapped hole of a given pitch is such

as to result in a flat equal to one-third of the basic flat (K^Xp). When the minimum hole is basic, its maximum major diameter will be above the basic major diameter by the amount of the specified pitch diameter tolerance plus

two-ninths of the basic thread depth.

(k) The minimum major diameter of a tapped hole is the basic major diameter. In no case, however, should the minimum major diameter of the hole, as results from a worn tap or cutting tool, be such as to cause it to be rejected on the mini- mum major diameter by a "go" plug gage made to the standard form at the

crest.
WRENCH FIT FOR THREADED STUDS 235

(I) The tolerance on the minor diameter of a tapped hole of a given piteh is one-sixth of the basic thread depth.

8. Illustbation.—The relations of the maximum and minimum major,

pitch, and minor diameters of stud and tapped hole specified herein are shown in Figures 71, 72, and 73.

STUO TAPPED

Fig. 72.

Illustration of loosest condition for class 5, wrench fit for threaded studs, one-half inch, 13 threads, set in hard materials

(b) CLASSIFICATION

1. Allowance and Tolerance Values.—Allowances and tolerances are

specified in Tables 116 and 117, inclusive, for coarse-threaded and fine-threaded studs set in hard materials—namely, cast iron, steel, and bronze. These are based upon data obtained in an experimental investigation and fulfill the conditions outlined in the above specifications.

4. TABLES OF DIMENSIONS

Tables 118 and 119 give recommended thread dimensions of studs and tapped

holes which meet the above specifications for coarse-threaded and fine-threaded studs set in hard materials. Also the limiting values of the torques at full engage- ment (lever-arm times force) which may be expected in the assembly of studs and tapped holes made to these dimensions are given.

18415°—29 16
NATIONAL SCREW THREAD COMMISSION

STUD TAPPED

HOLE

Fig. 73.

Illustration of tightest condition for class 5, wrench

fit for threaded studs, one-half inch, 13 threads, set in hard

materials
WRENCH FIT FOR THREADED STUDS 237

Table 116.Class 5, wrench fit for threaded studs, allowances and tolerances for

studs and tapped holes, coarse threaded studs in hard materials

Sizes Threads

}JX2l. JLJU.',l_l

Interference on

pitch diameter

Pitch diameter

tolerances 1 Errors in half angle consuming one-half

of pitch diameter

tolerances

Mini- mum

Maxi- mum oiuci Tapped

hole 2 Stud Tapped

hole

1 % 3 4 5 6 7 8

Inch Inch Inch Inch Deg. Min. Deg. Min.

I/a y± 20 0. 0003 0. 0018 0. 0007 0. 0008 16 25 Me 18 .0005 .0040 .0020 .0015 41 31 % 16 .0005 .0045 .0024 ' .0016 44 29 yl6 14 .0006 .0050 .0026 .0018 42 29

Yi 13 .0007 .0055 .0029 .0019 44 28

•M6 12 .0008 .0060 .0032 .0020 44 28 n 11 .0008 .0060 .0031 .0021 39 26

3/4... 10 .0009 .0065 . 0033 .0023 38 26 % 9 .0010 .0065 .0031 .0024 32 25

1 8 .0011 .0065 .0027 - . 0027 25 25 m 7 .0011 .0065 .0024 .0030 19 24

lYi 7 .0012 .0065 .0023 .0030 18 24 m 6 .0013 .0070 .0021 .0036 14 25

1 Inasmuch as a moderate difference in lead between stud and tapped hole (about 0.005 inch per inch) has been shown to improve the quality of a stud fit having minimum pitch diameter interference, no lead

tolerance is specified. Therefore, the tolerances specified for pitch diameter include all errors of pitch di- ameter and angle but not of lead. (See "6. Gages and gaging" herein.) Excessive lead errors, however,

should be avoided, as they increase the tendency of the stud to loosen when subjected to load. Columns

7 and 8 give, for information, the errors in angle which can be compensated for by half the tolerance on

pitch diameter given in columns 5 and 6.

2 The tolerances on the tapped hole given in column 6 are the same as those specified for class 4, close fit screws and nuts, with the exception of the M-inch size. Table 117.

Class 5, wrench fit for threaded studs, allowances and tolerances for

studs and tapped holes, fine-threaded studs in hard materials

Sizes Threads

per inch

Interference on

pitch diameter

Pitch diameter

tolerances 1 Errors in half angle consuming one-half

of pitch diameter

tolerances

Mini- mum

Maxi- mum Stud Tapped

hole 2 Stud Tapped

hole

1 2 3 4 5 6 7 8

Inch Inch Inch Inch Deg. Min. Deg. Min. H 28 0. 0005 0. 0034 0. 0018 0. 0011 58 35 Me 24 .0005 .0037 .0020 .0012 55 33 % 24 .0006 .0044 .0026 .0012 1 11 33 Me 20 .0008 .0044 . 0025 .0013 57 P0

Yi 20 .0007 .0050 .0030 .0013 1 9 30 Me 18 .0007 .0050 .0028 .0015 58 31 % 18 .0008 .0055 .0032 .0015 1 6 31

16 .0008 .0059 .0035 .0016 1 4 29

7A- 14 .0008 .0061 .0035 .0018 56 29

I. 14 .0009 .0069 .0042 .0018 1 7 29 m—- 12 .0009 .0067 .0038 .0020 52 28

12 .0011 .0060 .0029 .0020 40 28

ltt . 12 .0012 .0050 .0018 .0020 25 28

1 Inasmuch as a moderate difference in lead between stud and tapped hole (about 0.005 inch per inch) has been shown to improve the quality of a stud fit having minimum pitch diameter interference, no lead

tolerance is specified. Therefore, the tolerances specified for pitch diameter include all errors of pitch diameter and angle but not of bad. (See "6. Gages and gaging" herein.) Excessive lead errors, however,

should be avoided, as they increase the tendency of the stud to loosen when subjected to load. Columns

7 and 8 give, for information, the errors in angle which can be compensated lor by half the tolerance on

pitch diameter given in columns 5 and 6.

1 The tolerances on the tapped hole given in column 6 are the same as those specified for class 4, close-fit screws and nuts.
238 NATIONAL SCREW THREAD COMMISSION

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240 NATIONAL SCREW THREAD COMMISSION

5. SPECIFICATIONS FOR THREADING TOOLS

(a) FORM OF TOOLS FOR PRODUCING STUDS

The specifications given in Appendix 4 for tolerances on chasers, thread

milling cutters, roller dies, threading hobs, etc., are also applicable to tools used

for the production of threaded studs to the above specifications.

(b) TAPS

In order to produce tapped holes within the tolerances specified herein for class

5, wrench fit for threaded studs, the use of ground thread taps, for which specifi- cations are given in Appendix 4, is necessary.

(c) TAP DRILLS The essential requirement of a tap drill is that the hole produced by it shall be such that, after tapping, the minor diameter of the tapped hole shall be within the specified limits shown in Tables 118 and 119. Inasmuch as these limiting

dimensions for the minor diameter of the tapped hole are greater than those

specified in Section III for fits of classes 1 to 4, inclusive, the tap drills specified in Appendix 4 can not be used for class 5, wrench fit for threaded studs. In columns 13 and 14 of Tables 118 and 119 are given recommended sizes of tap

drills which lie within the specified limits on minor diameter; wherever possible these consist of existing stock sizes of drills. However, the size of hole produced

by a tap drill depends somewhat upon the method of grinding the drill, the

material drilled, the lubricant used, and the speed and feed of operation, so that the fixing of the tap drill size does not completely determine the diameter of the

drilled hole, and careful attention to these other factors is necessary.

6. GAGES AND GAGING

The fundamentals of this subject, as it relates to screw threads, are laid down

in Section III. The relatively close limits on pitch diameter specified for class

5, wrench fit for threaded studs, necessitate careful and accurate gaging of both the stud and tapped hole, particularly since the actual measurements

obtained depend somewhat upon the methods of gaging used. Considering first the case of minimum interference: The minimum stud and

maximum hole are selected by means of "not go" gages. With the usual or recommended forms of "not go" gages, the presence of lead errors does not

affect the gaging. It has been shown by the experimental data obtained that

this is a desirable condition, as the presence of a slight difference in lead between

stud and hole is an advantage, especially with minimum pitch diameter inter- ference. It is important, however, as with the other classes of fit, that the "not go" gage should check the pitch diameter only, for upon this the mini- mum tightness of a stud fit depends, assuming that the correct thread form and

smoothness of thread surface are maintained. In the case of maximum interference the maximum stud and minimum hole are selected by means of "go" gages, and these may or may not be the usual types of threaded plugs and rings. Plug and ring gages control pitch diameter,

lead, thread angle, maximum minor diameter of stud, and minimum major

diameter of hole. The minimum minor diameter of the hole being considerably

above basic, it is not controlled by the "go" threaded plug gage, and as it has been shown that a certain minimum clearance at minor diameter must be maintained, it is very important that the hole should be gaged further by means of a "go" plain plug gage. Gaging the tapped hole by means of a "not go" plain

plug gage is also desirable, but not strictly necessary. Gaging of the major diameter of the stud thread is not essential; this element may be controlled by the size of stock. Some means of controlling the minimum

minor diameter of the stud is, however, very desirable, particularly on studs of
COMMON SCREW THREAD PRACTICE 241

the smaller sizes, because the shearing strength of the stud depends upon this element. For this purpose the projection comparator is very useful, but

inspection of the cutting tool to assure a width of flat at the root of the thread

not less than J^Xp is sufficient. The use of thread micrometers or "go" cone-pointed snap gages for checking

the pitch diameter of the stud is good practice provided that the thread form is ascertained by optical inspection. Gaging for lead errors is not essential 'provided that the lead of the threading tools is maintained within the usual

limits of good commercial practice.

If the tap (ground thread tap) is a close fit in the hole after tapping—that is,

if the tap can not be screwed easily (without the use of a wrench) through the

hole after tapping—it may be assumed that the pitch diameter of the hole is very nearly the same as that of the tap. APPENDIX 6. COMMON PRACTICE AS TO THREAD SERIES

AND CLASS OF FIT FOR SCREWS, BOLTS, AND NUTS

The usual commercial practice as to application of thread series and class of

fit to screws, bolts, and nuts is indicated in Table 120. Table 120.

Common practice as to thread series and class of fit for screws, bolts, and nuts

Product Thread series Class of fit

2 3 Rough machine bolts Coarse Class 1, loose fit. Class 2, free fit. Class 3, medium fit. Do.

Do.

Do.

Class 2, free fit. Class 1, loose fit. Class 2, free fit. Do.

Class 1, loose fit. Class 2, free fit. Do. Do.

Class 3, medium fit. Class 2, free fit. Class 3, medium fit. Class 5, wrench fit. Class 2, free fit. Class 3, medium fit.

Semifinished machine bolts: General applications do Automotive vehicles Fine

Finished machine bolts: General applications Coarse.. Automotive vehicles _ . ... Fine

Aircraft do Machine screws Coarse or fine Machine-screw nuts: Numbered sizes .. _. ... . .. . do

Fractional sizes . do Cap screws ... . . .. do

Stove bolts Coarse..

Carriage bolts do

Step bolts do

Button-head machine bolts do

Set screws do Threaded studs: Nut end _ f....do : Stud end

\Fine

Coarse or fine ... . Tap bolts Coarse. . .. ...... Tap rivets . do APPENDIX 7. (1) DESIGN OF GAGES AND (2) GAGING

PRACTICES

1. REPORT OF THE AMERICAN GAGE DESIGN COMMITTEE 8 (ABRIDGED)

(a) HISTORY OF THE AMERICAN GAGE DESIGN COMMITTEE

The American Gage Design Committee was formed in December, 1926, to

consolidate for the benefit of industry at large the independent efforts which were

already in progress on the part of a number of large industrial concerns, repre9 For complete specifications see American Gage Design Committee report published as Commercial

Standard No. CS8-29 of the Department of Commerce.
242 NATIONAL SCREW THREAD COMMISSION

sentatives of United States Government bureaus and several of the leading gage manufacturers to simplify gaging practice through the adoption of standard

designs for gage blanks and component parts. The designs developed by the American Gage Design Committee are now available to everyone and will minimize the necessity for the manufacture of special gages of the simpler types. The committee was given full support and recognition by engineering societies, the American Standards Association, the Bureau of Standards, the War and

Navy Departments, and this commission. It should be pointed out, however,

that the major work of the committee was contributed by industry itself, many of the country's large industrial units in widely diversified fields being

represented by active membership on the committee. Joint meetings were

held with the commission throughout 1927 and 1928. Rapid progress was made in these meetings, and formal design standards were completed and adopted

for plain and thread-plug gages of all sizes up to 43^ inches diameter, and for plain and thread-ring gages of all sizes up to 4J^ inches diameter. The meetings of the committee were open, and ideas and suggestions from all branches of industry were welcomed and given careful consideration, it being the

earnest endeavor of the committee to crystallize the best design and construction

of gage blanks, handles, and component parts for plain and thread gages. The fullest cooperation was extended by all, proprietary patent rights being

waived by individual gage manufacturers for the general benefit of industry. In promulgating the new standards the committee has not intended to obsolete

existing stocks of gages in the hands of manufacturers or users; rather, it has been its intention to provide a standard which could be gradually adopted through

replacement of existing stocks. Representing the best ideas of industry at large, including gage makers and gage users, the American Gage Design Standards

should have whole-hearted support and be accepted and used by gage purchasers,

and should render obsolete the wasteful and costly practice of requisitioning gages to individual design standards, which has existed in many cases heretofore. Tool supervisors and standards departments of large industrial concerns are

particularly urged to adopt, as soon as practicable, the American Gage Design

Standards as a substitute for airy individual standards which may now be employed. The result will inevitablj- be the elimination of confusion in gage departments, and advancement in the direction of economy and quality of product.

The following, among others, have participated in the work of the American

Gage Design Committee:

Erik Aldeborgh, the Standard Gage

Co., Poughkeepsie, N. Y.

J. Chester Bath, John Bath & Co., Worcester, Mass. H. W. Bearce, secretary, Bureau of Standards, Washington, D. C. *fF. S. Blackall, jr., chairman of editorial subcommittee, vice president

and general manager, The TaftPeirce Manufacturing Co., Woonsocket, R. I. *JE. J. Bryant, Greenfield Tap and Die

Corporation, Greenfield, Mass.

*C. R. Burt, vice president, Pratt &

Whitney Co., Hartford, Conn.

* Member of standing committee,

t Member of editorial committee,

t Member of technical subcommittee.

Fred Colvin, editor American Machinist, Tenth Avenue and Thirty-sixth

Street, New York, N. Y.

{A. C. Danekind, manager's office, Building 44, General Electric Co., Schenectady, N. Y.

A. H. d'Arcambal, Pratt & Whitney

Co., Hartford, Conn.

C. F. Dreyer, Western Electric Co., Department 6871-1, Hawthorne Station, Chicago, I1L George M. Foster, Northern Electric Co., Montreal, Canada.

John Gaillard, mechanical engineer, A. S. A., 29 West Thirty-ninth Street, New York, N. Y.
AMERICAN GAGE DESIGN COMMITTEE 243

tJW. H. Gourlie, gage division, Pratt &

Whitney Co., Hartford, Conn.

A. Grieve, Chevrolet Motor Co., Detroit, Mich.

E. D. Hall, Western Electric Co., Hawthorne Station, Chicago, 111. E. A. Hanson, president, The Hanson- Whitney Machine Co., Hartford,

s Conn.

P. M. Herrick, Cadillac division, General Motors Corporation, Detroit,

Mich. H. D. Hiatt, Nash Motors Co., Racine,

Wis. W. L. Hindman, Dodge Bros. (Inc.), Detroit, Mich.

Commander H. B. Hird, Bureau of Engineering, Navy Department,

Washington, D. C. *Col- J. O. Johnson, chairman, chief, gage section, Ordnance Department,

3737 Munitions Building, Washington, D. C. C. V. Johnson, sales engineer, the John-Sons Gage Works, Hartford, Conn. JH. S. Kartsher, 3211 Sycamore Road,

Cleveland Heights, Ohio. *C. B. LePage, assistant secretary, A. S. M. E., 29 West Thirty-ninth

Street, New York, N. Y. JH. B. Lewis, Brown & Sharpe Manufacturing Co., Providence, R. I. A. M. Lord, Taylor Instrument Cos., Rochester, N. Y.

tL. M. McPharlin, the Studebaker

Corporation, South Bend, Ind.

J Paul V. Miller, manager, small tool department, the Taft-Peirce Manufacturing Co., Woonsocket, R. I. C. H. Moen, Muncie Products Co., Muncie, Ind. R. S. Newton, the New York Air Brake Co., Watertown, N. Y. W. J. Outcalt, standards section, General Motors Corporation, Detroit,

Mich.

*JD. W. Ovaitt, chairman of technical subcommittee, General Motors Corporation, c/o Buick Motor Co., Flint, Mich.

C. J. Oxford, chief engineer, National

Twist Drill & Tool Co., Detroit,

Mich.

Lieut. Col. E. C. Peck, Room 305, Lake Erie Bank Building, 1612 Euclid Avenue, Cleveland, Ohio. Louis E. Peck, general manager the ThreadweU Tool Co., Greenfield, Mass.

Charles M. Pond, manager small tool and gage division, Pratt & Whitney

Co., Hartford, Conn.

C. H. Reynolds, The Sheffield Machine

& Tool Co., Dayton, Ohio.

P. D. Ritchey, the Standard Gage Co., Poughkeepsie, N. Y. C. E. Rundorff, research department,

Buick Motor Co., Flint, Mich.

JA. W. Schoof, department 6871-2, Western Electric Co., Hawthorne

Station, Chicago, 111. A. J. Schwartz, United States Naval

Gun Factory, Navy Yard, Washington, D. C.

J. A. Siegel, Packard Motor Car Co., Detroit, Mich.

O. J. Snider, Cadillac Motor Car Co.,

Detroit, Mich. H. B. Stringer, Winter Bros., Wrentham, Mass. H. L. Van Keuren, the Van Keuren

Co., 12 Copeland Street, Watertown, Boston, Mass.

tC. E. Watterson, The Sheffield Machine & Tool Co., Dayton, Ohio.

+.W. H. Weingar, 88 Maplewood Avenue, West Hartford, Conn. K. D. Williams, Bureau of Engineering, Room 2326, Navy Department,

Washington, D. C. George R. Worner, Taylor Instrument

Cos., Rochester, N. Y.

Details of the American Gage Design Standards are explained by definitions,

cuts, line drawings, and dimensional tables in the pages that follow.

• Member of standing committee,

t Member of editorial committee.

X Member of technical subcommittee.
244 NATIONAL SCREW THREAD COMMISSION

(b) TERMINOLOGY

The following glossary is intended to clarify the meaning of certain technical terms employed in this report. The definitions are not intended to be general; rather they are specific as to their application to the American Gage Design

Standards. American Gage Design Standard: The caption "American Gage Design

Standard" has been adopted to designate gages made to the design specifi- cations promulgated by the American Gage Design Committee.

1. A plain cylindrical plug gage is a complete unthreaded internal gage of

single or double ended type for the size control of holes. It consists of handle and gaging member or members, with suitable locking means.

2. A progressive cylindrical plug gage is a complete unthreaded internal gage consisting of handle and gaging member in which the "go" and "not go"

gaging sections are combined in a single unit secured to one end of the handle.

3. A thread plug gage is a complete internal thread gage of either single or double ended type, comprising handle and threaded gaging member or members,

with suitable locking means.

4. The gaging member is that integral unit of a plug gage which is accurately

finished to size and is employed for size control of the work. In taper-lock gages, the gaging member consists of a shank and a gaging section.

5. The gaging section is that portion of the gage which comes into physical contact with the work. In the 1.510 to 4.510 inch plug range, the gaging section

is identical with the gaging member.

6. The shank (applied to taper-lock gages only) is that portion of the gaging

member which is employed for fixing the gaging member to the handle.

7. The term "taper-lock" designates that construction in which the gaging

member has a taper shank, which is forced into a taper hole in the handle. This

design is standard for plug gages in the range above 0.059 inch to and including

1.510 inches, is optional for plain cylindrical and thread plug gages in the range above 1.510 inches to and including 2.510 inches, and is standard for pipe thread

plug gages up to and including 2-inch nominal pipe size.

8. Lightening holes are unfinished drilled holes provided in the heavier sizes of gaging members for the sole purpose of reducing the weight of the gage.

9. The handle is that portion of a plug gage which is employed as supporting means for the gaging member or members.

10. The drift hole or drift slot is a small hole or slot provided in the side of a

taper-lock gage handle near the "go" end through which a pin or drift may

be inserted for the purpose of driving the gaging member out of the handle.

11. A plain ring gage is an unthreaded external gage employed for the

size control of external diameters. In the smaller sizes it consists of a gage body into which is pressed a bushing, the latter being accurately finished to size for gaging purposes.

12. A thread ring gage is an external thread gage employed for the size control of threaded work, means of adjustment being provided integral with the gage body.

13. The flange is that external portion of a large ring gage which is reduced in section for the purpose of lightening the gage.

14. The hub is the mid-section of a flanged ring gage. It determines the length of the gaging section.

15. The thread ring gage locking device is a means of expanding and contracting the thread ring gage during the manufacturing or resizing process. It also provides an effectual lock. It comprises an adjusting screw, a locking screw, and

a sleeve. For detailed description and illustration see pages 249 to 250.
AMERICAN GAGE DESIGN STANDARDS 245

16. Adjusting slots are radial slots provided in thread ring gages in order to

facilitate expansion and contraction of gage size by means of the adjusting

device. Adjusting slots always terminate in an adjusting slot terminal hole. 17. The locking slot is that slot which passes entirely through the wall of a

thread ring gage. In conjunction with the thread ring gage locking device it permits expansion and contraction of gage size.

(c) AMERICAN GAGE DESIGN STANDARD SPECIFICATIONS

* 1. Plain Cylindrical Plug Gage Blanks and Handles.—Two separate

designs have been adopted for plain cylindrical plug gages—a taper-lock design

for the range from 0.059 to 1.510 inches, and the reversible type for the range from above 1.510 to 4.510 inches. Use of the taper-lock design is optional for the size range from above 1.510 to 2.510 inches.

STANDARD Fig. 74.

Plug gage handles, Nos. 000 to 0, inclusive The groove in the "not-go" end of the handle is to distinguish it from the "go" end. The dimension Mis left to the discretion of the manufacturer.

(a) Taper-lock design.—It was felt that the taper-lock design was particularly well suited for the smaller sizes of plain plug gages. This type of gage is simple and economical of production. Gaging members are readily removable

from the handle when replacement is necessary. Complete dimensional toler- ances have been established for the mating parts of gaging members and handles,

insuring absolute interchangeability of gaging members and handles wherever

manufactured. General details of construction are shown in Figures 74 to 78, inclusive, and dimensions are giver; in Tables 121 and 122.

(6) Reversible design.—Consideration of simplicity and economy of manufacture and use will likewise dictate the choice of the reversible design in the larger

size ranges. At this time this design is not completely developed.

(c) Handles.—Handles for both taper-lock and reversible gages are the hex- agonal type. However, the use of round medium-knurled handles, while not recommended, is made optional in all sizes.
246 NATIONAL SCREW THREAD COMMISSION

MEDIUM KNURLoptional

TWO FLATS

•E—

1

EH

C-DRILL SIZE-\ h-A — 1 i

6

is

PIN REAMER, TAPER .25" IN 12" STANDARD

Fig. 75.

Plug gage handles, Nos. 1 to 5, inclusive

-A- - A—

—B— *c-*» B[- it,

3

-4 ^

\ * 1 —E Z/

60° INC. CHAMFER- TAPER .25* IN 12"

Fig. 76.Plain cylindrical plug gages, above 0.059 to 0.150 inch, inclusive — D A

h-c-H-H B

D

TAPER .25" IN I2,,J Fig. 77.

Plain cylindrical plug gages, above 0.150 to 0.240 inch, inclusive
AMERICAN GAGE DESIGN STANDARDS 247

I6

r

BREAK ALL CORNERS ^ALL TAPERS .25" IN 12' NOT GO —c- BPROGRESSIVE Fig. 78.

Plain cylindrical plug gages, above 0.240 to 1.510 inches, inclusive {optional above 1.510 to 2.510 inches)

60c

B h~l—-C—

60°INC. CHAMFERS LTAPER .25" IN 12" Fig. 79.

Thread plug gages, No, to No. 6 sizes, inclusive

B

D —-C-

<—EB —

-

60° CHAMFER ^TAPER .25" IN 12"

Fig. 80.Thread plug gages, No. 8 to No. 12 sizes, inclusive
248 NATIONAL SCREW THREAD COMMISSION

2. Thread Plug Gage Blanks and Handles.—The taper-lock and reversible designs have been adopted for thread plug gage blanks and handles and follow the plain plug gage standards with the exception that the length of thread- gaging members is slightly different in some instances. General details of conCONVOLUTION, BOTH ENDS. NOT LESS

THAN THREE FULL THREADS MUST

REMAIN ON "NOT GO" PLUG.

Fig. 81.

Thread plug gages, 34 t° Wi inches, inclusive (optional to 2}/2 inches) struction will be apparent from Figures 74, 75, 79, 80, and 81, and dimensions

are given in Tables 121 and 123.

3. Plain Ring Gage Blanks.—The use of the solid ring gage design for external size control, being fairly well established, the committee's work on GO NOT GO

4- MEDIUM KNUSL, gBEAK ALL CORKERS

ABOVE -SIP TO 1.510 tWCL. Fig. 82.

Plain ring gages, above 0.059 to 1.510 inches, inclusive plain ring gages was concerned chiefly with matters of proportion. In the

smaller sizes of plain ring gages it was felt desirable to employ a hardened

bushing pressed into a soft gage body, in place of the one-piece ring gage, and

this design has been adopted in the range from 0.059 to 0.510 inch. The single
AMERICAN GAGE DESIGN STANDARDS 249

piece gage is employed in all cases above 0.510, but gages in diameters above

1.510 inches are flanged, in order to eliminate unnecessary weight and facilitate handling. No dimensional difference exists between "go" and "not go" blanks

of identical size range, but an annular groove is provided in the periphery of "not go" blanks as a means of identification. General details of construction

are shown in Figures 82 and 83, and dimensions are given in Tables 124 and 125.

4. Thread Ring Gage Blanks.—The committee found universal accord as

to the superiority of the adjustable thread ring gage over the solid type, with the

result that all American Gage Design Standard thread ring gage blanks are equipped with an effective device for adjusting and locking the gage in the manufacturing or resizing processes. Of the many locking devices considered the

single-unit locking device was finally adopted as standard, as it permits a minimum

diameter of blank for a given size range, and provides a simple adjustment and

positive lock without introducing any mechanical stresses into the gage body

which might tend to create distortion after setting. Referring to Figure 84, the

construction and operation of this device is as follows: The adjusting screw is

JaP NOT 60

Fig. 83.Flanged plain ring gages, above 1.510 to 4-510 inches, inclusive threaded externally and internally and split longitudinally. Turning this screw

to the right exerts pressure on the sleeve against the shoulder in the left-hand

side of the gage here shown, thus spreading the ring. Once the ring has been

properly adjusted by means of the adjusting screw, the adjustment is locked by

tightening the locking screw. The tightening of the locking screw exerts a pull

between the shoulder immediately under its head and the internal threads of the

adjusting screw, which causes it to expand into the threads in the wall of the gage without exerting any extra pressure on the sleeve. Therefore, the clamping

is accomplished by expansion of the adjusting screw equally in all directions and not by the application of any eccentric forces that tend to distort the gage

or upset the adjustment. The locking pressure, it is seen, is taken up centrally

in the locking screw itself, as the reacting support is directly under the head

of the locking screw in the form of a shoulder in the gage. The sleeve, being

accurately fitted, serves as a large dowel to maintain the alinement of the gage. Three types of thread ring gage blanks have been provided, as illustrated in Figure 84: A thin flat disk type with one adjusting slot for all pitches and sizes, both "go" and "not go," up to and including 5/i & inch; a thin flat disk type with two adjusting slots for all sizes and pitches of both "go" and "not go" gages
250 NATIONAL SCREW THREAD COMMISSION

above %6 inch up to and including % inch, all fine pitches of both ''go" and "not go" gages above Y% inch up to and including 4% inches, and all coarse pitch "not

go " gages above Y% inch up to and including 4^ inches; and a thick flanged type

for all coarse pitch "go" gages above y2 inch up to and including 4^ inches. Dimensions for thread ring gage blanks covering the range from No. to 4>£ inches, inclusive, are given in Tables 126 and 127.
AMERICAN GAGE DESIGN STANDARDS 251

Table 121.

Dimensions of taper-lock plug gage handles

[For notation see figs. 74 and 75]

Handle

size A B

DrDl C D E (? ^4' J K L

No.

2 3 4 5 6 7 8 9 10 11 12

00000

12

InchesMeH

Me

3A

A

Inches

1%

22M

3

f No. 34

I (o.iii) / No. 29

I (0. 136) / No. 20

\ (0. 161)

i L

\ (0. 290)

Inches

} «.

}

5/i

J ^6

2 ^2

^ 25^2

J

Inch Hi by H

M2 by M6

34 by %

34 by A

Inch

/ 0.125

I .126

f . 155

I .156

/ . 180

I • 181

f .239

\ .240

f .309

\ 310

iVb. } 000

}

°

}

2

} 4

}

6

Inches A

Me%

' Me

56

Inch%2Me

Me

%2

5i

InchA

A

A

"AA

Inch A2

A2

A2He

He

3 m* 2 %2 J .409

\ .410 }

* *Me Me A %2

4 A 3H 37Ai %

/ .609

I .610 } » lHe Me Me 3A2

5 1A 4 25^2 Me J .809

I . 810 | } " lMe 34 % A

15 m 4 2^2 13^ Me / .809

\ .810 1 } » We 34 5A A

1 Optional range. Table 122.

Dimensions of taper-lock plain cylindrical plug gages

[For notation see figs. 76, 77, and 78]

Range

Handle

size No.

Go All Not go Progressive

Above In- cluding A B C E A A B F G

1 2 3 4 5 6 8 9 10 11 12 13 14

Inches

0.059

.105 .150

.240

.365

.510

.825

1. 135 U. 510

1 2. 010

Inches

0. 105 .150 .240

.365 .510

.825

1. 135 1.510

2. 010 2.510

00000

12

3

4

5

5

5

Inches IA2

1M

22H

2Me 2A

3H&A .

Inches %

Me

!%2 %

1IHm

1A

1A

2

InchA

Me

5A

%

%

A

1

l

1

Inch Inch

/ 0. 125

I .126

/ .155

Inches

} 3^2

InchMe

%2

Me%

A

5A

U

A

A

Inches Inches Inch Inches

A

A

H

A

Me

3A

l

. I06 ij

(. . 1S1 J .239

\ .240

/ .309

i .310

f .408

\ .410

/ .608

\ .610

/ .808

\ .810

f .808

t .810

/ .808

\ -810

} lMe

} m

}

} l^Me

} 2A

} m

} D4

2Me 2H2A

3Me 3M

4Hm

lMe

134 1%

2J4

23/^ 2%

2%

Me%

345*M

A

A

%

1

134 134

134 m

2

1 Optional range. 18415°—29 17
NATIONAL SCREW THREAD COMMISSION

Table 123.

Dimensions of taper-lock thread plug gages 1 [For notation see figs. 79, 80, and 81]

Thread sizes, inclusive Handle

size No.

Go Both Not go B D E A

1 3 4 g 7 9

Inches Inches Inch Inch Inch Inches Inch Nos. to 3 000 H H

f 0. 125

} 3^2 Me I !l26 Nos. 4 to 6 00 i%2 Me Me / .155

\ .156 ) Hi

J %a

Nos. 8 to 12... 1%2 1%2 A

f .180

I .181 | 1^2 %2 H to 5Ae 1 1V4 72 7* Va

f .239

\ .240

\f 1Mb J- 710 716 A to A- 2 1% % H H

/ . 309

I

'• 310 } m %

?16 10 Y4 3 1%

2^6

2§6

J4Me%

J .408

\ .410

f .608

} 1H

} HMb

} 2^

72 a to m 4 M

1H-7 5 1M 1

I .610

f .808

\ .810

/ .808

\ .810 u

5 2% i$ 1

} 2H %

1H-12 2?4 To

f .808

} 1^-12 }

i \ .810 2>o H

The reversible type of design is recommended for thread plug gages in all sizes above VA inches diameter. Table 124.

Dimensions of plain ring gages 1 [For notation see fig. 82] Range A Ring

size No. B C D hole 2 E F3

Length

of bushing Above Including

1 2 3 i 5 6 1 8 9 Inches

0. 059 .150 .240

.365

.510

.825 L 135

Inches

0. 150 .240

.365 .510

.825

1. 135

1. 510

00

12

3

45

Inches

15A&±0. 010 !Me± .010 m ± . 010 m =fc • 010 1% ± . 010 2A ± . 010

2^2 d= • 010

Inches Me±0. 010 H± • 010 Me± . 010 M± • oio *Me± .010 ia ± .oio lMe± . 010

34+0.000 - .005 Me+ .000 - .005 Me+ .000 - .005 M+ .000 - .005

Inch A*

A2Me

He

3A2%a

%2

Inch

732 He

3^2 732 %2

732

732

Inch H

Men

1 Material: To 0.510 inch, inclusive: Shell, cold rolled steel ; bushing, tool steel, hardened. Above 0.510 to 1.510: Tool steel, hardened.

» Bushing is +0.020 inch for fitting.

* Depth of groove to be A of width. Table 125.

Dimensions of plain ring gages (flanged)

[For notation see fig. 83] Range A Ring

B A+ D

Above Including

size No.

2 3 i 5 6 Inches Inches Inches Inches Inch

1.510 2. 010 6 A A

2. 010 2. 510 7 m A A

2. 510 3. 010 8 5A 1 Me

3. 010 3. 510 9 6 1 Me

3. 510 4. 010 10 m 1A H

4. 010 4. 510 11 7A 1A H
AMERICAN GAGE DESIGN STANDARDS

| X X X XX XX XX XX XX

3 |le

x x x x x x xx xx xx

P a iimii nil mm mm mm mm

1

5 1 S 11 11 11 11 11

III " s ^ h glllllit 1111 ilil ii» 1118 881

Drill R

3 xfxixi

b s s xixt

se mss mss

'*!

ss #ies

Drill P i miii m®m

H a | X X X XX XX XX XX XX

a |* *.* x # # x xx xx xx

|xx# x# i?x x# ## _

N s

a» | £ £ £ ^ & & £ & & 3? X

ao 1 * * . .* - * M I * J s|

fc. i ^ ^ ^ ^ ^ & j£ ^ ^ n &

* x ? iff x f . i

* x

5 55 H H H

O

•*

Thread

sizes,

inclusive

! s s il i 1

I | \.\

it II il i! il
254 NATIONAL SCKEW THREAD COMMISSION

Table 127.

Dimensions of thread ring gage locking device

[For notation see fig. 84]

Adjusting screw A K

Minor

diam. B C

E

F H J

Size P. D. Size P. D. Drill

1 2 3 i 5 6 7 8 9 10 11

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No. 12-28.—

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2. GAGING PRACTICES AND TYPES OF GAGES

The production of accurate parts is primarily a matter of constant vigilance

and of training of workmen. The smaller the tolerances which are to be maintained, the more complete the inspection or gaging system must be. In order

to secure satisfactory results, the manufacturing tools provided must be suffi- ciently accurate, and the manufacturing methods must be sufficiently reliable, to produce the required results. After tools and methods of proved reliability are provided, it is necessary to watch the wear on the tools or changes in their set-up

to insure that the required conditions are maintained. This is accomplished by
GAGING PRACTICES 255

periodical tests of the tools, by periodical gaging of the product, and sometimes

by both. A screw thread comprises several elements: First, the major diameter; second, the pitch diameter; third, the minor diameter; fourth, the angle of the thread; and fifth, the lead. The most difficult element of a screw thread to gage is the

lead. Lead-testing devices for checking tools and gages are available, but, in general, their operation is too slow for use as production inspection equipment.

In addition, the lead is the most important element of a screw thread as regards the nature of the contact between the surfaces of the mating parts. Further-

* more, the result of an error in lead is almost double that of an equal error in diameter as regards interchangeability. For exacting threaded work, if the method of inspection of the product does not effectively detect lead errors, the

tools used must be carefully inspected for lead. In order to reduce the possibilities of disagreement to a minimum, the manufacturer should strive to produce

parts well within the specified limits rather than close to the limiting sizes.

(a) Thread Micrometers.—Thread micrometers are sometimes used to measure the pitch diameter of taps and screws. Thread micrometers should be

calibrated periodically against a master gage, to avoid errors due to wear on the

anvils of the instrument. As thread micrometers give no indication of lead and

angle errors, the results of tests made with thread micrometers alone can not be

taken as conclusive.

(6) Thread Snap Gages.—Thread snap gages are generally adjustable and

have contact points consisting of cone-pointed anvils, wedge-shaped prisms with

rounded edges, serrated or grooved plates, or grooved or threaded cylinders adjustably mounted and suitably spaced in a U-shaped frame. These gages are used to some extent in gaging external threads and have the advantages that work may be inspected with great rapidity by the single motion of passing it between the anvils of the gage and given a visual examination for clearance as well as a tactile inspection. The positions of the anvils are set to a setting gage, and the anvils are then clamped in position and sealed. The usual form of cone-pointed snap gage has a single point on each side of the frame, and is an effective "not go" gage. It does not, however, fully meet

the requirements for a "go" gage, as it does not check the lead, and, therefore,

i must be supplemented with some type of, indicating gage to check the lead when used for checking pitch diameter, angle, and thread form. Also, as it

j checks only a single diameter at a time, the "go" snap gage must be tried at a

I series of points to determine whether the maximum diameter of an external thread

[ is within the tolerance. When provided with three contact points, two on one

! side spaced an integral number of threads apart and one on the other, such a gage

i checks the lead for progressive, but not always for local or periodic lead errors,

I and, thus, it more nearly fulfills the requirements for a "go" thread gage. Thread snap gages having multiple toothed contact points, that is, toothed

f blades, serrated or grooved plates, or grooved or threaded cylinders, are made in a

t variety of forms, either as separate or combined "go" and "not go" gages,

i The fit of a screw in such a gage is affected by variations in pitch diameter, lead,

) and angle of the screw, and the gage accordingly may be used as a "go" gage.

, Such gages have been found suitable only for the less accurate classes of work,

j such as the loose and free fit classes. Thread micrometers and thread snap gages are used for testing the product

; as it is produced. As these instruments do not test all elements of the screw thread, a " go " gage should always be used as a supplementary test. Thread micrometers are very effective means of checking against the change in [set-up due to

i wear on tools, etc.
256 9 NATIONAL SCREW THREAD COMMISSION

(c) Thread Ring Gages.—Thread ring gages are extensively used to measure

the threads on screws. These are usually adjustable to suitable setting gages. When the product is to be within specified limits, "go" and "not go" gages

are required. The use of such gages gives some information as to lead and

angle errors as well as pitch diameter errors.

(d) Thread Comparators.—A recent development in the art of measuring

threaded parts is the optical thread comparator, which embodies the principle of gaging in an optical projection system. In addition to giving a rapid indication

of whether the elements of the screw thread he within the limiting dimensions

specified, such instruments furnish more detailed information as to the errors in screw threads than is usually obtained by means of mechanical gages, particularly as to irregularities in thread form, lead, and diameter. These instruments can be adapted to measure taps and other threading tools. The available forms of projection comparators differ somewhat in design and

principle, but each consists primarily of a source of parallel fight, such as an

electric arc or concentrated filament lamp with condensing lens system, a projection lens system, a screen upon which the magnified shadow image of the work

is projected, and a device for holding the work in position in front of the projection lenses. The screen consists of a tolerance chart on which two outlines

of the correct thread form at the magnification used are spaced one above the other a distance equal to the tolerance multiplied by the magnification. The

chart and gage holder are adjusted to position by projecting the shadow image

of a setting gage and adjusting to bring the outline of the shadow image and

certain lines of the chart into coincidence, after which the system may be used

as a gaging device. The above types of optical thread comparators are applicable to external threads. Two types of optical thread comparators for internal threads are being developed by the Bureau of Standards, one known as an "optical coin- cidence thread gage," and the other as a "stereoscopic thread gage." 10 (e) Indicating Gages.—An indicating thread gage has movable contact

points, which are set to a setting gage, and is intended to give an exact indi- cation of the variations of the dimensions of a screw thread within the specified

limits, rather than to show merely that the thread is within, or outside of, the

specified limits, as is the case with limit gages. In such gages the movable

contact points actuate a multiplying lever system, or other means for magnifying

their motion, and the amount of the motion is registered on a graduated dial or

scale. Indicating gages are made according to a variety of designs, some to indicate progressive lead error only, some to indicate pitch diameter only, some

to indicate both separately but on the same gage, others to indicate the major

and minor diameters as well, and still others to indicate the apparent size. They

have been applied almost exclusively to external threads. Those which indicate the apparent size may be considered as most nearly fulfilling the requirements of a gaging system. However, those indicating lead errors are very useful in controlling lead errors in threading tools and screw-thread products. Also

certain types can be used to indicate the variation in roundness on pitch or major diameters.

(f) Thread Plug Gages.—At the present time the most practical means of gaging threaded holes or nuts is by the use of thread plug gages. When the product is to be within specified limits, "go" and "not go" gages are required.

The use of such gages gives some information as to lead and angle errors as well as pitch diameter errors. A correct "go" plug gage will reject any parts which exceed the minimum dimensions specified.

10 Described in N. S. T. C. Communication No. 132, pp. 20-23; Mar. 6, 1928.
GAGING PRACTICES 257

One practice of inspecting tapped holes is first to inspect the tap, and then to

test the tapped holes periodically with "go" and "not go" gages. The tap can be watched for wear by testing the tapped holes with a "go" thread gage. One widely used practice consists of using a "go" thread plug gage, and a

"not go" plain plug gage for the minor diameter. One practice of inspecting taps is to measure the several elements, such as

pitch diameter, angle, and lead. Another practice consists of tapping a hole with

each tap before it is issued from the tool crib and testing these tapped holes with

"go" and "not go" thread plug gages. Sometimes the tap is tested after it is returned to the tool crib. If it is correct,

it is replaced in its proper compartment. If it has worn below the limits, it is discarded and work produced by it is checked and corrected when necessary.

(g) Plain Gages.—"Go" and "not go" plain cylindrical plug gages are used for inspecting the minor diameter of the tapped hple. Plain ring or snap

gages are used for inspecting the major diameter of the screw. When used,

it is recommended that the "go" inspection gage be a ring gage and the "not go" inspection gage be a snap gage. The working gages may be a combined

"go" and "not go" snap gage.

(h) Gear-Tooth Caliper for Thread Thickness.—A device which is particularly useful in the measurement of thread thickness of Acme screw threads,

or of tools for producing them, is the gear-tooth caliper. With this device the depth at which the measurement is made is controlled by means of a vernier or micrometer and the thickness is determined by means of another.

(i) Testing of Gages.—Gages should be tested periodically for wear and

to insure that the gages are properly distributed. When successive inspections

in the same plant are involved, it is good practice to inspect all gages of the same nominal size against each other periodically, and to distribute these gages

so that the earlier inspections are made with those which are the greatest amount

inside of the component limits, while the later inspections are made with those gages closest in size to the component limits. The original testing of a thread gage should include measurements of diameters, lead, and angle. If these elements test satisfactorily, the later inspection

need be only measurements of pitch diameter.11 h Methods of measuring pitch diameter of screw thread gages are described in Appendix 2, p. 184.

INDEX

Page

Accuracy, control of..., 198-204 Acme screw threads 149-166

historical.. 149 Allowance (definition) 17 (numerical values) 30, 38, 103, 157, 161, 237 American Gage Design Standards 241-254 American National Acme form of thread 150 Acme screw threads 149-166 coarse-thread series 23 fine-thread series . 24

fire-hose coupling threads 100 form of thread 20-21, 79, 176, 232 hose-coupling threads 99 lock-nut threads 113 standard hose connections 167-173

straight pipe threads 110 taper pipe threads 107 threads for electric sockets and bases... 174-176

12-pitch thread series 176-180 Angle errors, diameter equivalent of 30,

33, 34, 38, 103, 123-124, 184, 237 Angle of helix (see Helix angle) 17 Angle of thread (definition) 17 Arrangement of report 15 Authorization by Congress 8 Axis of screw (definition) _ 17 Base of thread (definition) _ 17 Basic size (definition) 18 Bolt and nut proportions 133-149 Bolt and screw lengths 134, 139 Bolt-body diameters 134, 138 Bolts and nuts, screw threads for 20-59

carriage. 148 countersunk 148 fin-neck 148 ribbed.... 148 square-neck 148 machine... 134 button-head 148 finished. 135 rough 135 semifinished. 135 plow 148 round unslotted head 148 step 148 tap 135 wrench head... 133 Cable drilling tool joints... 167 Cap screws (see Screws, cap) 137, 147, 149 Carriage bolts (see Bolts, carriage) 148 Chaser, thread... 200, 207, 221, 226 Chasers, die-head 221, 226 Class 1, loose fit 25, 28, 42, 46, 81, 85, 86 Acme 153 Class 2, free fit. 25, 30, 43, 47, 81, 85, 88 Acme 157 Class 3, medium fit 25,33,

44, 48, 82, 85, 90 Acme 161

Page

Class 4, close fit 25,37, 45,49,82,85, 92 Acme 162 Class 5, wrench fit for threaded studs 232-241

Classification of fits... 25,28,81,153 Clearance, crest 18

at major diameter. . 21,150

at minor diameter 21,150,235 Close fit, class 4 ._ 25, 37, 45, 49, 82, 85, 92 Committees, sub 11-13,208,242

Cnmnfl.rat.nrs. thread Core diameter (see Minor diameter) 16 Crest (definition) 17 Crest clearance (definition) 18 Cutter, thread milling 201,207 Cutting of screw threads- 199-201, 204-221, 240 Cutting torch hose connections 167-173 Definitions _ _ 1fi-1 8. 244-245 Depth of engagement (definition) 17 thread (definition). 17 Diameter, major 16 minor 16 pitch 16 Diameters, body — 134,138 Die-head chasers 221,226 Dimensions (tables of thread) — .— 23-24, 42-59, 85-93, 100, 103, 108-109, 111, 113, 130,

139, 152, 157, 161, 175-179, 237-239. Direction of tolerances on—

gages 61 hose couplings - 100 pipe threads 107 screw and nut 26,80

Electric socket threads. 174 Engagement, depth of 17 length of 17,28,78,107

Errors, control of lead . 198 Error, diameter equivalents of lead and angle 183 European trip 13 External thread (definition) 16

Fillets in Acme threads.. — 150,164,230 Finish (definition) — 18

Fit, close, class 4 25, 37, 45, 49, 82,85,92

(definition) — 18

free, class 2 _ 25, 30, 43, 47, 81, 85, 88

loose, class 1.. _. 25, 28, 42, 46, 81, 85, 86 medium, class 3__ 25, 33, 44, 48, 82, 85, 90

Fits, Acme threads — 153 common practice 241 Form of Acme threads 150 American National coarse and fine threads 21 fire-hose coupling threads 99 hose-coupling threads 99 pipe threads 106 threadsofspecial diametersand pitches 79 Free fit, class 2 25, 30, 43, 47, 81, 85, 88 259
260 INDEX

Page

Gage adjusting slots (definition) 245 Gage classification. 61, 63, 94, 116, 180 design standards 241-254

drift hole (definition) 244

drift slot (definition) _ 244 flange (definition) 244 handle (definition) _ 244 hub (definition) 244 lightening holes (definition) __. 244 Jocking slot (definition) _ 245 plain cylindrical plug (definition) 244 plain ring (definition) 244 plug, reversible design 245 taper-lock design 245 practice recommended 64 progressive cylindrical plug (definition).. 244 shank (definition) 244 thread plug (definition) 244 ring (definition) 244 thread ring locking device (definition).,. 244 thickness 257 Gages, American standard 254-265 American National Acme screw threads. 163-166 American National coarse and fine threads 60-77 American National fire-hose coupling

threads 104-105 American National pipe threads 116-126 check.... _ _. 61, 117, 119 Class X 63,94,180 Class Y 63, 94, 180 Class Z 63,94,180

classification as to accuracy 63 design and construction of_ 241-254 dimensions of 68-77,

105, 108-109, 165-166, 169-173 direction of tolerances on 61

electric socket 175

for wrench fit 240 "go" and "not go" 60,250-252 hose connection 169 indicating 198,199,256 inspection.. 61, 105, 117, 121, 163, 169, 175 lamp base... 175 marking of... 19,66,95 master 61,116,119 measurement of 184, 197 mechanical 61 optical 61 plain... 64,244-252,257

setting or check 61, 117, 119 specifications for 62-77, 94-96, 104-105, 119-

126, 163-166, 169-173, 175, 180, 240-241, 245-254

testing of... 65,119-122,257 thread plug 62, 244-252, 256 thread ring 62, 244-254, 256 thread snap. 255 threads of special diameters and pitches. 94-96 tolerances on 61,63-

67, 94-96, 104, 119-123, 163-164, 169-173, 175, 180 wear on 63,122 working.. 61, 118, 121-122, 163, 169, 175 Gaging 60-62, 118-119, 163, 240-241, 254-257 fundamentals of.. 60-62,116,163 member (definition) _ 244

Page

Gaging, object of. 60 practices 118-119,254-257

section (definition) _ 244 Grinding thread 203 Hearings, public. 14 Helix angle (definition).. _ 17 Historical 7, 149 Hob, threading 201 Hobs, tooth outlines of. 207, 228 Hose-connection gages 169-173 Hose connections for torches 167-169 Interchangeability 8,25,60 Internal thread (definition). 16 International standardization 15 Lamp-base threads 174-176 Lapping of screw threads 204 Lead (definition) 17

errors, control of 198-199 diameter equivalent of. 30, 33, 34, 38, 103, 124, 183 Lead screw, Acme thread 161-163 commercial (definition).. 161 precision (definition) _. 162 Length of engagement (definition) 17 pipe thread _ 107 Lengths, bolt and screw 134 tolerances on.. 134 Limits (definition) 18 Line pipe 167 Lock-nut threads _ 113 Long screw joints. 112 Loose fit, class 1 25, 28, 42, 46, 81, 85, 86 Machine bolts (see Bolts, machine) 134 Machine-screw nuts 136, 146 proportions 149 Major diameter (definition) 16 Manual on pipe threads 105, 114 Marking of gages 19, 66, 95

tools 19,220 Measurement of pitch diameter 184, 192 thread gages 184, 197 thread thickness 193-197, 257 wire methods of 184-197 Measuring pressure. 62, 186 Medium fit, class 3... 25, 33, 44, 48, 82, 85, 90 Members of commission. 10, 14 Micrometers, thread 255 Minor diameter (definition)... 16 uniform, of nut _ 26, 152 Net tolerances, basis of 181 Neutral zone (definition) 18 Nomenclature (see Terminology) 16-20, 244-245 Notation 20,21,106,110-112,151 Number of threads (definition) ._ 17 Nut 16 proportions 133, 135-136, 142-146 Nuts 133-149 castellated- 136,144 jam, finished 136, 145 jam, semifinished 136, 145

fight. 136,145 machine screw 136, 146 regular finished 136,143 regular rough. _ 136, 142 regular semifinished 136, 142 stove bolt 136,146
INDEX 261

Page

Oil-well casing threads 167

drilling equipment ---- 167 Organization of commission 10-14 Outside diameter (see Major diameter) 16 Pipe dimensions, tables of 114-116

specifications.. ._. 167 thread gages 119-126 manual 105,114 threads, straight - H°

taper 107 Pitch (definition) 17 diameter (definition) 16 measurement of 184-192 uniform, of minimum nut 26, 152 Plow bolts 148 Practice for fits and thread series 241 Pressure, measuring 62, 186 Procedure of commission 14 Proportions, screw, bolt, and nut 133-149 Public hearings 14 Report, arrangement of 15 Rethreading tools — 225 Rivets, tap 148

Roll, threading 202 Roller dies 202 Rolling of screw threads 201-203 Root (definition) 17 Rotary drilling taper joints 167 Screw 16 axis .- 17 lengths 134 proportions 133-149 thread (definition) 16 plug gage (definition)— 244 ring gage (definition) 244 threads, American National Acme 149-166 cutting of 199-201, 204-221, 240

finishing of 203

for oil-drilling equipment 167 miscellaneous special 167-180 on tubing 221 regular 20-77

rolling of 201-203

special 78-96,167-180

special 12-pitch._ 176-180

tools for cutting 199-201, 204-221, 240 Screws, cap 137, 147, 149 hexagon head _ . 137,147 machine 149

set 148 headed 148 headless slotted 148 wood.. _.. 127-133 Set screws (see Screws, set) 148 Side of thread (definition) 17 Standard temperature 62 Stove bolt nuts.. 136, 146 proportions 149 Straight pipe threads __ 110 Sucker rod specifications 167 Symbols 18-20,107 Tap bolts 135

drill sizes 221-227,238,240

rivets 148

Page

Taper, effect on thread depth 106 threads, measurement of. 188-191 Taps 200,208-221 Acme thread 230-232 American National form of thread 208-221 dimensions and tolerances 208-219, 230-232 marking of 220 shape of cutting edge for 220, 231 Temperature, standard 62 Terminology. 16-20, 244-245 Thread (see Screw thread). 16 angle... 17 depth (see Depth of thread)... 17 ring gage locking device (definition) 244

series (see American National)... 22, 79,99,107,130,151,174,177 common practice 241 Threads, internal and external 16 Threading tools, specifications. 204-232, 240 Tolerance (definition) 18 increments, Acme thread thickness 153, 154, 158 pitch diameter 80, 183 Tolerances: Acme thread 152-163 derivation of.. 181-184

direction on gages. 61 gage - - 63-67, 95-96, 104, 119-123 hose couplings 100-103 Numerical values

Class 1, loose fit 30, 86 Class 2, free fit.... 33,88 Class 3, medium fit 34, 90

Class 4, close fit. 38,92 on length of screws, etc 134 pipe threads 107,110 (product specifications) - . 25-41, 83-93, 100-103,

107, 110, 127-131, 134, 152-163 screw and nut 26 wood screws 127,130-131 wrench openings— 148 Tool, single point 207, 228 Tools for Acme screw threads.. 227-232 form of 205-208, 227-230 marking of 19,220 rethreading for fire-hose threads 225 tooth outlines.. 205-208, 228-232 Torques, wrench fit, for studs 235, 238-239 Tubing, screw threads on 221 Uniform minimum nut 25, 80, 152

Utility of report 15 Welding torch hose connections 167-173 Wire methods of measurement 184-197 Wires, measurement of. 186

sizes of— 191-193

specifications for 186 Wood screws.. 127-133

specifications 127 standard sizes 132 thread series. 130 tolerances 127,130-131 Working-barrels .— 167 Wrench fit, class 5, for threaded studs 232-241 Wrench head bolts 133-141 Wrench openings 137, 148 O