U.S. DEPARTMENT OF COMMERCE

BUREAU OF STANDARDS

REPORT OF THE

NATIONAL SCREW THREAD

COMMISSION

(REVISED 1933)

MISCELLANEOUS PUBLICATION NO. 141

May 28, I93U

SHrtATA

||fXOML BUKSAXJ OF SfAHDAEDS MISCfflLLAJSBOUS PUBLICATION 1JO. iHl

1933 BEPOBT OF KiE K&DIOHAL SCREW THREAD COMMISSION

Page 68, last line (above footnote) change "thread"

to "threaded".

Page 75? Table 32 > in column headed "3/^"» change

".6993" to ",6903"

Page 87, running head, change "ECIAL" to "SPECIAL".

Page SI 3 Table UU, add to title, "and American

IJational fire-hose coupling threads".

Add "(max.)" to heading "Inside diameter of

nipple, C".

Ada the following to the table:

l/2j

JJL/2

U 1/2

f'7 1/2 jl il5/l6 S 11/16 11 A , [2 l7/32,h l/k

Fire nose J 16 1 i/8 ji 1/16 ji 3/16 [5/16 5 1/12 IS

S|6~ 1 1/S II l/l6 j n/l6 5 A

6" 13 17/321.5

iiU ll 1 /Uil ',/! 6 1 15/16 7/i6 !U 17/32.3 3

A

Page 92 > Table U5, footnote 2, last line, change "nipplee"

to "nipple".

Page ikk, first line, change "15" to "I50".

Page 151, line 35, change "know" to "hnov.ii".

Page 162, line 2, change "0.010" to "0.020".

line 3, change "0*005" to "0.010".

lines 5~S > change to read as follows:

"5. CLEARANCE AT MATCH DIAMETER.- A clearance shall

be provided at the major diameter by making the major

diameter of the nut or threaded hole 0.020 inch larger

than basic for 10 or less threads per inch, and 0.010 inch

larger than basic for more than 10 threads per inch.

Fig. 53 , change "ALLOWANCE Oil MAJOR DIAMETER m

0.01 INCH" to "ALLOWANCE CfS MAJOR DIAMETER15 . Page l66, column S, change ".2Sl6" to ".2716".

column 9, change ".277U" to ".267^".

column 12, change ".28^7" to ".28^3".

MTIOEAL BUREAU 0? STANDARDS

U.S. DEPARTMENT OF COMMERCE

DANIEL C. ROPER, Secretary BUREAU OF STANDARDS

LYMAN J. BRIGGS, Director REPORT OF THE

NATIONAL SCREW THREAD

COMMISSION

(FOURTH EDITION, REVISED 1933)

AS APPROVED APRIL 10, 1933

Miscellaneous Publication No. 141

UNITED STATES

GOVERNMENT PRINTING OFFICE

WASHINGTON : 1933

For sale by the Superintendent of Documents, Washington, D. Ci Price 15 cents
PREFACE

Progress in commercial screw thread practice, which is based very

extensively on the standards established by the National Screw Thread

Commission, has been such as to require several revisions and some

additions to the standards promulgated in the Commission's 1928

report. This report, the fourth to be published, embodies necessary

changes. The experience of the Commission demonstrates that technical standards, to be useful, cannot be static, but must be revised

and adapted to meet changing requirements.

Major revisions of the previously published standards consist in: The addition of the 1%-, ?>}{-, 3%-, and 4-inch sizes to the coarse- thread series ; the addition of the 1 %-inch size to the fine-thread series

;

the elimination of all sizes above 1 % inches from the fine-thread series; the elimination of the small machine screw sizes from class 4, close

fit ; the addition of four sizes and pitches to the hose-coupling threads

;

the revision of tolerances for pipe thread gages; and the revision of

the specifications for Acme threads, including a new recommended

series of diameters and pitches. The volume of the report has been

reduced by the elimination of standards for body dimensions of bolts,

nuts, and screws, and standards for the design of gage blanks, except

by reference to the latest revisions of other published standards for

these products.

New material added to the body of the report includes specifications

for an 8-pitch and a 16-pitch thread series for special applications,

which, together with the previously published 12-pitch series, are presented as a separate section. These series, demanded by industry,

constitute in effect an amplification of the fine-thread series, and are a substitute for the sizes above 1% inches in that series which have

been deleted. A new table of tolerances for gages used in the inspection of class 4, close fit product is also included.

In the appendixes the recommended practice for threading tools

has been deleted. The Commission's purpose to stimulate muchneeded activity in the standardization of taps, die-head chasers, and

other threading tools has been fulfilled. Published standards for such

tools, which have received general recognition, are referred to in the

report.

The assistance and cooperation of many individuals, manufacturers,

and users of screw-thread products, tools, and gages, and of the

American Society of Mechanical Engineers, the Society of Automotive Engineers, the American Standards Association, and several of

the sectional committees organized under its procedure, the Federal

Specifications Board, the United States Army, the United States

Navy, the Bureau of Standards, the National Board of Fire Underwriters, the American Petroleum Institute, the International Acetylene Association, the Gas Products Association, and the American Gage

Design Committee, are gratefully acknowledged by the Commission.

ii
CONTENTS

Page Preface n

Approval by the Commission and transmittal to the Secretaries of War,

Navy, and Commerce vii Approval by the Secretaries of War, Navy, and Commerce viii Section I. Introduction 1

1. Historical 1 2. Need for definite specifications 2

3. Authorization of Commission by Congress 2

4. Organization of the Commission 3

(a) Preliminary meeting 3

(&) Members 3

(c) Officers 4

(d) Personnel on European trip 4

(e) Present organization 5

(J) General procedure 5

5. Arrangement of report 6 Section II. Terminology 7

1. Definitions 7

(a) Terms relating to screw threads 7

(&) Terms relating to classification and toler- ances 8

2. Illustrations showing terminology 9

3. Symbols 9 Section III. Screw threads for bolts, machine screws, nuts, tapped

holes, etc 11

1. American National form of thread 11

(a) Specifications 11

(6) Illustration 12

2. Thread series 12

(a) American National coarse-thread series 14

(&) American National fine-thread series 15

3. Classification and tolerances 16

(a) General specifications 16

(6) Classification of fits 19

4. Tables of limiting dimensions 31

5. Gages 50

(a) Fundamentals 50

(&) Specifications for gages 52

Section IV. Uniform pitch screw thread series for high-pressure fastenings, railroad applications, machinery components, etc__ 68

1. Form of thread 68

2. Thread series 1 68

(a) American National 8-pitch thread series 68

(&) American National 12-pitch thread series__ 68

(c) American National 16-pitch thread series. _ 68

3. Classification, tolerances, and limiting dimensions- 69

4. Gages 75

Section V. Screw threads of special diameters, pitches, and lengths

of engagement 76

1. Form of thread 76

2. Thread series 76

3. Classification and tolerances 77

(a) General specifications 77

(b) Classification of fits 79

4. Tables of dimensions 80

(a) Arrangement of tables 80

(&) Rules for use of tables 81

(c) Examples 81

5. Gages 82

* Partially new material not included in report revised June 22, 1928. Ill
IV CONTENTS

Page

Section VI. American National hose-coupling and fire-hose coupling threads 91

1. Form of thread 92

2. Thread series 92

(a) American National hose-coupling threads. _ 92

(6) American National fire-hose coupling threads 94

3. Allowances and tolerances 94

4. Tables of limiting dimensions 96

5. Gages 98

(a) Gages for American National fire-hose coupling threads 98

Section VII. American National pipe threads 99

1. Form of thread 100

(a) Specifications 100

(6) Illustration 100

2. Symbols 101

3. Thread series 101

(a) American National taper pipe threads 101

(6) American National straight pipe threads. _ 104

(c) American National locknut threads 106

4. Tables of pipe dimensions 107

5. Gages 109

(a) Fundamentals 109

(b) Specifications for gages 109

(c) Gaging practices 111

Section VIII. American National screw, bolt, and nut proportions 1 116

Section IX. Miscellaneous special threads 117

Section IX A. Screw threads for oil-well drilling equipment 117

Section IX B. American National standard hose connections for welding

and cutting torches 117

1. Standard dimensions 118

2. Optional features 118

3. Gages 118

Section IX C. American National rolled threads for screw shells of electric sockets and lamp bases 123

1. Form of thread 123

2. Thread series 124

3. Gages 125

(a) Gaging of lamp base screw shells 125

(6) Gaging of socket screw shells 125

(c) Tolerances on gages 125 Appendix 1. Derivation of tolerances 127

1. Pitch diameter tolerances 127

(a) Tolerances for fastening screws 127

(6) Tolerances for screw threads of special diameters, pitches, and lengths of engagement- 127

2. Relation of ]ead and angle errors to pitch diameter

tolerances 128

(a) Diameter equivalent of lead error 128

(6) Diameter equivalent of angle error 128 Appendix 2. Wire methods of measurement of pitch diameter 129

1. Size of wires 129

2. Specification for wires 130

3. Methods of measuring and using wires 131

4. Measurement of pitch diameter of American National

straight threads 132

5. Measurement of pitch diameter of American National

taper threads 133

6. Measurement of pitch diameter of thread ring gages. 135

7. Wire methods of measurement of thread thickness of Acme threaded plug gages 138

i Partially new material not included in report revised June 22, 1928.
CONTENTS V

Page

Appendix 3. Control of accuracy of thread elements in the production of threaded product 143

1. Introduction 143

2. Fundamental factors 143

(a) Control of tooth outlines 143

(6) Control of lead errors 144

3. Cutting of screw threads 145

(a) Single-point tool 145

(6) Thread chaser 146

(c) Tap or die 146

(d) Milling cutter 146

(e) Threading hob 147

4. Rolling of screw threads 147

(a) Threading roll 148

(6) Thread-rolling dies 148

5. Finishing of screw threads 149

(a) Grinding 149

(6) Lapping 150

6. Gaging practices and types of gages 150

(a) Thread micrometers 150

(6) Thread snap gages 150

(c) Thread ring gages 151

(d) Thread comparators 151

(e) Indicating gages 151

(/) Thread plug gages 151

(g) Plain gages 152

(h) Gear-tooth caliper for thread thickness 152

(i) Testing of gages 152 Appendix 4. Class 5, wrench fit for threaded studs (tentative specifica- tions) 152

1. Form of thread 152

2. Thread series 152

3. Classification and tolerances 152

(a) General specifications 152

(6) Classification 154

4. Tables of dimensions 154

5. Gages and gaging 160 Appendix 5. Common practice as to thread series and class of fit for screws,

bolts, and nuts 161 Appendix 6. American National Acme screw threads (tentative specifica- tions) 161

1. General and historical 161

2. Terminology 161

3. American National Acme form of thread 161

(a) Specifications 161

(6) Illustration 162

4. Thread series 1 162

5. Classification and tolerances 163

(a) General specifications 163

(6) Limiting dimensions and tolerances 164

6. Gages 167

(a) Fundamentals 167

(6) Gage tolerances 167 Index 169

2 Partially new material not included in report revised June 22, 1928.

APPROVAL BY THE COMMISSION AND TRANSMITTAL TO

THE SECRETARIES OF WAR, NAVY, AND COMMERCE

Hon. George H. Dern

Secretary oj War

Hon. Claude A. Swanson

Secretary of the Navy

Hon. Daniel C. Roper

Secretary oj Commerce

April 10, 1933.

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, approved June 22, 1928, herewith submits its report

revised to 1933, for your acceptance and approval, in accordance with

Public Act No. 201, approved July 18, 1918 (c. 156, sec. 2, 40 Stat. 913); as amended by Public Act No. 324, approved March 3, 1919

(c. 96, 40 Stat. 1291); Public Resolution No. 34 (H.J.Res. 299, 66th

Cong.), approved March 23, 1920; Public Resolution No. 43 (H.J.Res.

227, 67th Cong.), approved March 21, 1922; and Public Act No.

125, approved April 16, 1926 (c. 148, sec. 1, 44 Stat. 297).

Lyman J. Briggs,

Chairman.

J. O. Johnson, Colonel, U.S.A.,

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

Appointed by the Secretary of War.

C. S. Gillette, Commander, U.S.N.,

J. PI. Buchanan, Lieut. Commander, U.S.N.,

Appointed by the Secretary oj the Navy.

F. O. Wells,

Appointed by the Secretary oj Commerce jrom nominations

by the American Society oj Mechanical Engineers,

Geo. S. Case,

Earle Buckingham,

Appointed by the Secretary oj Commerce from nominations

by the Society oj Automotive Engineers. vn
VIII APPROVAL AND 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.Res. 299, 66th Cong.), Public Resolution No. 43 (H.J.Res. 227,

67th Cong.), and Public Act No. 125 (H.R. 264, 69th Cong.), is hereby

accepted and approved.

(Signed June 1, 1933) George H. Dern,

Secretary of War.

(Signed June 5, 1933) Claude A. Swanson,

Secretary of the Navy.

(Signed June 3, 1933) Daniel C. Roper,

Secretary of Commerce.
1933 REPORT OF THE NATIONAL SCREW

THREAD COMMISSION

AS APPROVED APRIL 10, 1933

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 one-fourth 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 country.

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 machine-screw thread series which provided smaller

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.

1
2 NATIONAL SCREW THREAD COMMISSION

2. NEED FOR 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 for 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 denned 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 quantity production

of machine parts is standardization of form and dimensions of parts,

which involves also the specification of limiting dimensions of the manufactured product in order that interchangeability 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 dif- ficulty 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 elimination of

unnecessary sizes, and the securing of interchangeability, 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 cannot 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, roundness, diameter, and length; whereas

in a screw-thread fit it is necessary to consider roundness, 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 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 Public Joint 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.):
ORGANIZATION AND PROCEDURE 3

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 repre- sentatives 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.

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. Dr. Lyman J. Briggs, Acting Director of Bureau

of Standards, Washington, D.C, succeeding

Dr. G. K. Burgess July 2, 1932. On nomination by the American Society of Mechanical

Engineers:

James Hartness September 21, 1918.

F. O. Wells September 21, 1918. Ralph E. Flanders, succeeding James Hartness. _ December 15, 1920. Luther D. Burlingame, succeeding Ralph E. Flanders December 10, 1924.
4 NATIONAL SCREW THREAD COMMISSION

Appointed by the Secretary of Commerce—Continued.

On nomination by the Society of Automotive Engineers: Date appointed H. T. Herr September 21, 1918. E. H. Ehrman September 21, 1918. 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. Army 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, 1920.

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, U.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. Roger W. Paine, lieutenant commander, U.S. Navy, Bureau of Engineering, succeeding Comdr. Harry B. Hird. August 20, 1928. Herman A. Spanagel, lieutenant commander, U.S. Navy,

y Bureau of Ordnance, succeeding Lt. Comdr. D. P. Moon June 22, 1929. John H. Buchanan, lieutenant commander, U.S. Navy,

Bureau of Ordnance, succeeding Lt. Comdr. Herman

A. Spanagel June 22, 1932.

C. S. Gillette, commander, U.S. Navy, Bureau of Engineering, succeeding Lt. Comdr. Roger W. Paine July 7, 1932.

(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. Robert Lacy, first lieutenant of Engineers, U.S. Army, assistant secretary. A. W. Coombs, stenographic reporter. (d) 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
ORGANIZATION AND PROCEDURE 5

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.

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 Engineeis, U.S. Army (technical secretary).

(e) Present Organization.—At the time of publication of this

1933 revised report the Commission comprises the following:

Members:

Dr. Lyman J. Briggs, chairman.

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

F. O. Wells.

Col. John O. Johnson.

Prof. Earle Buckingham.

George S. Case.

Lt. Comdr. John H. Buchanan.

Comdr. C. S. Gillette. H. W. Bearce, secretary.

Staff (Bureau of Standards)

D. R. Miller, technical investigator.

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

(J) 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.

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.
6 NATIONAL SCREW THREAD COMMISSION

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 screw- thread 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

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 arranged

in the foliowing order:

1. Form of thread.

2. Thread series.

3. Classification and tolerances.

4. Tables of dimensions.

5. Gages.
DEFINITIONS OF TERMS 7

SECTION II. TERMINOLOGY

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

words and terms which best convey alike to the producer and user of 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. 2—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 (Jormerly known as

"

outside diameter 11 ). —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 (jormerly known as

11 core diameter 11 ).—The

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

"minor 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

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 — ^ r fttt—j :—

r

• 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 oj 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.

2 These terms are here defined because of possible confusion arising from the fact that an "internal member" has an "external thread," and vice versa. For the sake of brevity an external thread is hereinafter

referred to as a "screw," and an internal thread as a "nut."
8 NATIONAL SCREW THREAD COMMISSION

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

the root.

13. Axis oj 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 Kelating to Classification and Tolerances.—

1. Allowance.—An intentional difference in the dimensions of matingparts. It is the minimum clearance or the maximum interference

which is intended between mating parts. It represents the condition

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

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. 44781 These are

series: Maximum pitch diameter

Minimum pitch diameter.

0. 4478.

. 4404

Tolerance . 0074

Minimum pitch diameter
SYMBOLS AND MARKING 9

2. ILLUSTRATIONS SHOWING TERMINOLOGY

Figures 1 and 2 illustrate the use of the terms and symbols used in

the report as herein defined.

Figure 1.Screw-thread notation:

3. 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

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

Number of threads per inch n

Lead ^= N

182129—33 2
10 NATIONAL SCREW THREAD COMMISSION

Pitch or thread interval ^ =

n

Helix angle s Tangent of helix angle ^=

3 14159X-S

Width of basic flat at top, crest, or root F

Depth of basic truncation /

Depth of sharp V thread 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

Figure 2.

Screw-thread notation. Additional symbols for American National Pipe Threads are given

in section VII.

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 "LH"

shall follow the class of fit. No symbol is used to distinguish right-
AMERICAN NATIONAL FORM OF THREAD 11

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 specify a threaded part 1 inch diameter, 8 threads Mark

per inch, class 1 fit 1"—8NC—1

Threaded part 1 inch diameter, 8 threads per inch,

class 2 fit, left hand 1"—8NC—2LH

American National fine thread series: Threaded part 1 inch diameter, 14 threads per inch,

class 4 fit 1" —14NF—4

American National 8-, 12-, or 16-pitch thread series: Threaded part 1 inch diameter, 12 threads per inch,

class 3 fit l"—12N—3

Threaded part 1% inches diameter, 8 threads per inch,

class 2 fit, left hand iy2 "—8N—2LH

American National form, special pitch:

Threaded part 1 inch diameter, 18 threads per inch,

class 2 fit l"—18—NS—2

Threaded part 1% inches diameter, 20 threads per

inch, class 3 fit, left hand 1 %'

'

—20NS—3LH

American National pipe threads: American National taper pipe thread. Threaded

part 1 inch diameter, 11^ threads per inch 1"—HYiNPT

American National straight pipe thread 1"—lljiNPS

American National fire-hose coupling threads and

American National hose-coupling threads: Threaded part 3 inches diameter, 6 threads per inch_ 3"—6NH

Threaded part 1 inch diameter, 11^ threads per inch. 1"—lljiNH

The number of threads per inch shall 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 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 7 ', 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.

(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

X

p.

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

i n^nnnv i 0.649519

h = 0.649519 X 1p, or h= ' n
12 NATIONAL SCREW THREAD COMMISSION

where

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

h = basic depth of thread

4. Clearance at 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

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

than 83% percent of the basic thread depth. (See fig. 17, p. 31.)

5. Clearance at Major Diameter.—A clearance shall be provided at the major diameter of the nut by removing from above the

basic thread form an amount such that the width of flat shall be less than YsXp, but not less than j^Xp.

(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.

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 certain 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 FORM OF THREAD 13

Figure 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

7i= number of threads per inch i?= 0.866025 p depth of 60° sharp V thread h—0. 649519 p depth of American National form of thread

%/i=0.541266 p maximum depth of engagement

i£i 8 /i=0.613435p .F= 0.125000 p width of flat at crest and root of American National form /= 0.108253 p] = \&H >depth of truncation
14 NATIONAL SCREW THREAD COMMISSION

(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

Threads

per inch, n

Major

diameter, D

Inches

64 0. 073

56 .086 48 .099 40 . 112 40 .125 32 .138 32 .164

24 .190

24 .216

20 .2500

18 .3125

16 .3750

14 .4375

13 .5000

12 .5625

11 .6250

10 . 7500

9 .8750

8 1. 0000

7 ]. 1250

7 1. 2500

6 1. 3750

6 1. 5000

5 1. 7500 m 2. 0000

2. 2500

4 2. 5000

4 2. 7500

4 3. 0000

4 3. 2500 4 3. 5000 4 3. 7500

4 4. 0000

Pitch diameter, E

Inches

0. 0629

.0744

.0855 .0958

.1177

.1437 .1629

.2175 .2764

.3344

. 3911 .4500

.5084

.5660 .6850

.8028

.9188

1. 0322

1. 1572

1. 2667

1. 3917

1. 6201

1. 8557

2. 1057

2. 3376

2. 5876

2. 8376

3. 0876

3. 3376

3. 5876

3. 8376

Minor

diameter, K

Metric

equivalent of major

diameter

Inches

0. 0527

.0628 .0719

.0795

.0925 .0974

.1234

.1359

.1619 .1850

.2403

.2938

. 3447 .4001 .4542

.5069

.6201 .7307 .8376

.9394

1. 0644

1. 1585

1. 2835

1. 4902

1. 7113

1. 9613

2. 1752

2. 4252

2. 6752

2. 9252

3. 1752

3. 4252

3. 6752

mm

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

34. 925

38. 100

44. 450

50. 800

57. 150

63. 500

69. 850

76. 200

82. 550

88. 900

95. 250 101.600

Pitch, V

Inch

0. 01562

. 01786

. 02083

. 02500

. 02500

. 03125

. 03125

. 04167

. 04167

. 05000

. 05556

. 06250

. 07143

. 07692

. 08333

. 09091

. 10000

. 11111

. 12500

. 14286

. 14286

. 16667

. 16667

. 20000

. 22222

. 22222

. 25000

. 25000

. 25000

. 25000

. 250C0

. 25000

. 25000

Depth

of thread,

h

Inch

0. 01015

.01160

,01353

. 01624

. 01624

, 02030

. 02030

. 02706

. 02706

. 03248

, 03608

, 04059

. 04639

, 05413

. 05905

, 06495

. 07217

. 08119

. 09279

, 09279

. 10825

, 10825

, 12990

. 14434

, 14434

, 16238

, 16238

. 16238

, 16238

. 16238

, 16238

. 16238

Basic width

of flat,

Inch

0. 00195

. 00223

. 00260

. 00312

. 00312

. 00391

. 00391

. 00521

. 00521

. 00625

. 00694

. 00781

. 00893

. 00962

. 01042

.01136

. 01250

. 01389

. 01562

. 01786

. 01786

. 02083

. 02083

. 02500

. 02778

. 02778

. 03125

. 03125

. 03125

.03125

. 03125

. 03125

. 03125

Mini- mum

width

of flat at major

diameter of nut,

p/24

Inch

0. 00065

. 00074

. 00087

. 00104

. 00104

.00130

. 00130

. 00174

. 00174

. 00208

. 00231

. 00260

. 00298

. 00321

. 00347

. 00379

. 00417

. 00463

. 00521

. 00595

. 00595

. 00694

. 00694

. 00833

. 00926

. 00926

. 01042

. 01042

. 01042

. 01042

. 01042

. 01042

. 01042

Helix angle at basic pitch diameter,

11

Beg. Min.

3122

2 11

1 55

Basic

area of

section

at root

of thread,- irKi

4

6. 7205

7. 9183

9. 2143

10. 6084
AMERICAN NATIONAL COARSE AND FINE THREAD SERIES 15

(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

Threads

per inch, n

Majoi

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,

s

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. 3750

1. 5000

Inches

0. 0519 .0640

.0759

.0874

.0985 .1102

.1218

.1460

.1697 .1928

.2268 .2854

.3479

.4050

.4675

.5264

.5889

.7094

.8286

.9536

1. 0709

1. 1959

1. 3209

1. 4459

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. 2067

1.3917

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

34. 925

38. 100

Inch

0. 01250

.01389

. 01562

. 01786

. 02083

. 02273

. 02500

. 02778

. 03125

. 03571

. 03571

. 04167

. 04167

. 05000

. 05000

. 05556

. 05556

. 06250

.07143

. 07143

. 08333

. 08333

. 08333

. 08333

Inch

0. 00812

. 00902

.01015

.01160

. 01353

. 01476

. 01624

. 01804

. 02030

. 02320

. 02320

. 02706

. 02706

. 03248

. 03248

. 03608

. 03608

. 04059

. 04639

. 04639

. 05413

. 05413

. 05413

. 05413

Inch

0. 00156

. 00174

. 00195

. 00223

. 00260

. 00284

. 00312

. 00347

. 00391

. 00446

. 00446

. 00521

. 00521

. 00625

. 00625

. 00694

. 00694

. 00781

. 00893

01042

01042

01042

01042

Inch

0. 00052

. 00058

. 00065

. 00074

. 00087

. 00095

. 00104

.00116

. 00130

. 00149

. 00149

. 00174

. 00174

. 00208

. 00208

. 00231

. 00231

. 00260

. 00298

. 00298

. 00347

. 00347

. 00347

. 00347

Beg. Min.

4 23

3 57

3 45

3 43

3 51
16 NATIONAL SCREW THREAD COMMISSION

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

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.

flncludes screw-thread work of rough corn- Class 1, loose fit ] mercial quality, where the threads must

| assemble readily, and a certain amount

[ of shake or play is not objectionable. flncludes the great bulk of screw-thread

Class 2, free fit J work of ordinary quality, of finished

| and semifinished bolts and nuts, machine

[ screws, etc. Class 3, medium fit flncludes the better grade of interchangeable

\ screw-thread work.

{Includes screw-thread work requiring a fine snug fit, much closer than the medium 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-thread 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.

2. Uniform 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.3 —(a) The tolerances specified represent the ex- treme variations permitted on the product.

3 Recommendations and explanations regarding the application of tolerances are given in appendix 1.
CLASSIFICATION AND TOLERANCES 17

(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.

« €<?3S/3p

« JIM

Figure 4.Illustration of tolerances, allowance (neutral space) , and crest clearances

for class 1, loose fit. (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.)

(jf) 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
18 NATIONAL SCREW THREAD COMMISSION

pitch diameters of the same respective classes and pitches with the

following exception: 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 fiat (%Xp) at the root when the pitch

<S v g> \ Xf < Q

SCREW NUT

Figure 5.Illustration of loosest condition for class 1, loose fit, one-fourth inch,

20 threads. 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.

(h) 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.

(i) The maximum major diameter of the nut of a given pitch is suchfas to result in a fiat equal to one third of the basic flat (&Xp)
CLASSIFICATION AND TOLERANCES 19

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

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.

Figure 6.

Illustration of tightest condition for class 1, loose fit, one-fourth inch,

20 threads. NOTATION D= major diameter E=pitch diameter K=minor diameter

A = 0. 0325= basic thread depth

(k) 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 Iji diameters. (For longer lengths

of engagement see section V, p. 76.)

(b) CLASSIFICATION OF FITS

1. Class 1, Loose Fit.—(a) Definition.—The loose-fit 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.
20

Table 3.—' NATIONAL SCREW THREAD COMMISSION

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. 24.

20.

18- 16. 14.

13.

12. 11.

10. 9.. 8_.

7__ 6-

5_.

4K> 4..

Inch

0. 0007

.0007

.0007

.0008

.0009 .0009

.0010

.0011

.0011 .0012

.0013

.0015

.0016

.0018

.0021 .0022

.0024

.0026

.0028

.0031

.0034

.0039 .0044

.0052

.0057 .0064

Inch

0. 0024

.0025 .0026

.0028

.0031 .0032

.0034

.0036

.0038

.0043 .0046

.0051 .0057

.0063 .0070

.0074

.0079

.0085

.0092

.0100

.0111 .0124

.0145

.0169 .0184

.0204

Inch

0. 0007 .0007

.0008

.0008

.0009

.0009

.0010

.0010

.0011 .0012

.0013 .0015

.0016 .0018

.0020

.0021 .0023 .0025 .0027

.0029

.0032 .0036

.0042

.0049

.0053

.0059

Beg. Min^

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

tolerance cannot, therefore, be used on pitch diameter unless the lead and angle of the thread are perfect. Col- umns 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 the "go" gage.

2 Between any 2 threads not farther apart than the length of engagement. This class has an allowance on the screw to permit ready assembly

even when the threads are slightly bruised or dirty.

(6) 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

diameter of the minimum nut is the theoretical pitch diameter for

that size.

(c) Maximum screw below basic}—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. (d) Allowance and tolerance values.—Allowances and tolerances are

specified in table 3.

2. Class 2, Free Fit.—(a) Definition.—The free-fit class is intended

to apply to interchangeable manufacture where the threaded members

4 The maximum minor diameter of the screw is above the basic minor diameter as shown in fig. 4.
CLASSIFICATION AND TOLERANCES 21

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.

JD a P/TCH

h- BAS/C THPEAO DEPTH

- 0.6,49519 p

Heavy Zw£ Shows

Bas/c S/Z.E

Figure 7.Illustration of tolerances and crest clearances for class 2, free fit: (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.
22 NATIONAL SCEEW THREAD COMMISSION

Table 4.—Class 2, free fit, tolerances for screws and nuts (no allowances)

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

564844

40

3632

2824

20.

18.

16.

14. 13.

12. 11. 10. 9_. 8-

7-

6.. 5-4H

4__

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

Inch

0. 0017

.0018 .0019

.0020 .0022

.0023

.0024 .0025

.0027

.0031

.0033 .0036

.0041 .0045

.0049

.0052

.0056

.0059 .0064

.0070

.0076 .0085

.0101

.0116 .0127

.0140

Inch

0. 0005

.0005 .0005

.0006

.0006

.0007

.0007 .0007 .0008

.0009 .0010

.0010

.0012

.0013

.0014

.0015

.0016

.0017 .0018

.0020

.0022

.0025

.0029

.0033 .0037

.0040

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 cannot, therefore, be used 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.

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

(c) Maximum screw basic. 5—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.

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,

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

that the tolerances are smaller.

5 The maximum minor diameter of the screw is above the basic minor diameter, as shown in fig. 7.
CLASSIFICATION AND TOLERANCES 23

NOTE: DOTTED LINE SHOWS BASIC SIZE

SCREW NUT

NOTJT/ON

O - major diameter E-pitch diameter

K — minor dj arnste r h = .0325 - basic thre ad depth

Figure 8.

Illustration of loosest condition for class 2, free fit, one-fourth inch,

threads.

SCREW

4

11

N!|r,

4»

Figure 9. -Illustration of tightest condition for class 2, free fit, one-fourth inch, 20

threads. NOTATION D=major diameter E=pitch diameter K=minor diameter h=0.0325 = basic thread depth
24 NATIONAL SCREW THREAD COMMISSION

(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.

Table 5.

Class 8, 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 2

72.

64.

56. 4S_ 44_

40. 36.

32. 28.

24.

20.

18. 16. 14.

13.

12.

11. 10. 9.. 8„

7_.

6..

5._

4..

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

Inch

0. 0013

.0013 .0014

.0015

.0016

.0016

.0017 .0018

.0019 .0022

.0024

.0026 .0030

.0032

.0036

.0037

.0040 .0042

.0045

.0049 .0054

.0059

.0071

.0082

.0089

.0097

Inch

0. 0004

.0004 .0004

.0004

.0005

.0005

.0005 .0005

.0005

.0006

.0007

.0008

,0010 0011 0012

0012

.0013 ,0014 0016

0017

,0020

,0024

,0026

,0028

1 The tolerances specified for pitch diameter include all errors of pitch diameter, lead, and angle. The full tolerance cannot, therefore, be used 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.

2 Between any 2 threads not farther apart than the length of engagement.

(c) Maximum screw basic.&-—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. 4. Class 4, Close Fit.—(a) Definition.—The close-fit class is intended for threaded work 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

The maximum minor diameter of the screw is above the basic minor diameter, as shown in fig. 10.
CLASSIFICATION AND TOLERANCES 25

fl - BAStC THREAD

DEPTH- O. C4QS/9p

//£AY/ Shows

Figure 10.

Illustration of tolerances and crest clearances for class 8, medium fit.

182129—33 3
26 NATIONAL SCREW THREAD COMMISSION

NOTE: DOTTED LINE SHOWS BAS/C SIZE

O ,

£ Q

NOTA T/ON

ma/or d/am e ter* E-pitch diannet&r

K = minor d/Qmeter

h ~.032S=has/c thread ofepth

SCREW NUT

Figure 11.

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

20 threads.

NO)

CD «0

Figure 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
CLASSIFICATION AND TOLERANCES 27

AJEAVX L/zs/E Shows

3as/c S/z^

Figure 13.

Illustration of tolerances, allowance (interference), clearances for class 4» close fit. and creat
28 NATIONAL SCEEW THREAD COMMISSION

screw-thread products belonging in this class it will be necessary to use precision tools, 7 gages made to special tolerances for this class (see

table 21, p. 58), 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 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 series 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 4, close fit, allowances and tolerances for screws and nuts

Threads per inch

Interfer- ences or negative 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

28-

24-

20.

18.. 16.

14. 13.

12.

11.. 10. 9-

8-7—

«... 5-

4...

Inch

0. 0002

.0004

.0004

.0004

.0005

.0005

.0006 .0006

.0007

.0008 .0009

.0010

.0011 .0013

Inch

0. 0011 .0012

.0013

.0015

.0016

.0018

.0019

.0020

.0021

.0023 .0024

.0027 .0030

.0036

.0041 .0044 .0048

Inch

0. 0003 .0003

.0004

.0004 .0005

.0005

.0005

.0006 .0006

.0007

.0007

.0008

.0010 ,0012

,0013 ,0014

Deg. Min.

35

3330

31

29

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

tolerance cannot, therefore, be used 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 the "go" gage.

* Between any 2 threads not farther apart than the length of engagement.

7 Including positive control of taps and dies by means of a lead screw. See p. 145.
CLASSIFICATION AND TOLERANCES 29

V 1 \ f SCREW NUT

Figure 14.

Illustration of loosest condition for class 4, close fit, one-fourth

inch, 20 threads.

Figure 15.

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

Z>= major diameter E=pitch diameter K=minor diameter

A =0.0325= basic thread depth
NATIONAL SCREW THREAD COMMISSION

Pitch - Inch

Figure 16.

Relation of maximum and minimum pitch diameters of classes 1, 2, 3, and 4 fits to basic pitch diameters.
DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS 31

4. TABLES OF LIMITING 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.
NATIONAL SCREW THREAD COMMISSION

Basic major

diamete s .nisi iiiii urn iiiii urn

Si1

slim mil mil iiiii iiiii

1

1

si ,11111 mil mil mil ling

1

I

1

.2 2

.mil Sim mil mil urn

"|d rA rA rA rA rA rA

1

1

OS slim mil iiiii mil mil

I 1

oc s n!i! iiiii mis iiiii urn

Minor

diameter, maximum

i jIHSI IIIII IIIII Hill

"|o rA tA rA rA rA

1

1

co s inii urn iiiii mil iiiii

J

1 I jinn mil iiiii mil iiiii

1

i

,11111 iiiii iiiii urn urn

1 1

Jim mil tint iiiii iiiii

Threads per

inch SS 05001- t^ooo^

<£ 53

jjjjj jjjji iiiii am aai
DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS

Hi! Uli

<N <N <N CO CO CO CO ^ mm mm cicicico CO CO' CO ^

sill IIII

CM* Oi CSI CN CO CO* CO CO

IIII IIII

<m' cm' (N iM' CO CO

- CO CO

iiii mm oi d (N CM CO CO CO CO

IIII IIII

CM CM im' cm' CO* co" CO CO

1111 IIII

tA d <N <N Ol CO CO CO

111! 1111

(M'cMIN'Cn' cococo'co

fill 1111

CM CM CM Ci CO CO CO CO

IIII 1111

im' cm" cm cm' co' co" co' co"

IIII IIII

CsfCMfNCS cocococo"

^rJH t»< -tft rj< t}< Tf< TH

NCM
NATIONAL SCREW THREAD COMMISSION

aj 2

„§!§§§ IIIII IIIII Hill

r

m

S3 itilll IIIII iiiii iniam

i

I

i S smm iiiii mil mil

3 I

i

s iiiiii mm iiiii mil

!

Inches 0.

0604

.0715 .0820 .0913 .1043 .1118 .1378 .1541 .1801 .2060 .2630 .3184 .3721 .4290 .4850 .5397 .6553 .7689 .8795 .9858

i i

CO ililii IIIII IIIII IIIII

!=• 1

Inches 0.

0538

.0641 .0734 .0813 .0943 .0997 .1257 .1389 .1649 .1887 .2443 .2983 .3499 .4056 .46C3

.5135 .6273 .7387 .8466 .9497

J

i iB illill IIIII IIIII IIIII

wg i 1

US jilill §§ill IIIII Iiiii

1

GO

Major

diameter 111 1

illill IIIII Hill IIIII

IIP I

jiiiii iiiii nm mil

1

slilil IIIII IIIII lllil

p SSSSS = S»«"-

I02 iiiji HiN iiiii iiiii

JJJJJ JJsai &&& sbbUS
DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS

iiiii nil mi

mil rH r-4 ^ r-! mi mi ci <M* <N CM CO CO CO CO ^ mil ^•^•^•^^ mi mi cn t>i -i CM coco'co'co

^^^^^ mil mi mi cicicici coco* coco* mil ,4 ,-.* ,-* h

nil mm r-! <n <m* <n cn* co co co co

IIIII IIII Illl

cm' cm* cm' <m* cn" e mil mirH mi ci <n Ci <M*CO*CO (

iiiii

r-5 —i i-i r-i i-i nil mi <n* cm* cm* cm co co co co"

iiiii

^ _; _; mi mi cm' cm' cm' <N CO CO CO CO mil miCM CM* CM CM miCOCOCOCO

11111 1111 Illl

^ r-4 CS CM CM CM COCOCOCO

illli Illl Illl

iH * i-l <-4 CM* CM CM' (N CO CO CO* CO IT*
36 NATIONAL SCREW THREAD COMMISSION

Hi

!

I

i

Hill lilli 11111 IIIII Hill lili IIII

^^^^^^^oic^csico CO CO CO

lilll 11111 Hill 11111 IIIII llll IIII

HH ^H^^^fN (NNNW CO CO CO Hill mil mil !§!!! mil §111 ifti

'^J r-4 T—H r-H t-H rH N N N fi CO CO CO CO mil siiii urn mil mil mi mi rH rA^^i^^ oioioici coco coco Hill Hill IIIII mil mil mi mi oiesi<Nc^ co co co co mil niii urn mil urn ^^^^•^ mi mi c-i csi CN CO CO CO

II

I

lilli Bill II!!! IIIII !H8 II! llll

^•^^^^^csje^ c-icococo inn iiiii iiiii mil mil mi nil \A HHrtHH C^CSi!N-CNi CO CO CO CO mil mm iiiii milrt mmhh^hh mi mi rifidN co co co" co

illlll IIIII Hill 11111 IIIII llll llll

^^•^•^ CSlC<!C<)Oi CO CO CO CO

iiiii iiiii iiiii iiiii iiiii

IN nil mi

iNNNM CO CO CO

II

££3^8 £2222 £2'

2d<
DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS

III

2 Inches 0.

2500

.3125 I .8750 1.

0000 1.

1250 1.

2500 1.3750 1.

5000 1.7500 2.0000 2.2500 2.5000 2.7500 3.0000 3.

2500 3.5000 3.

7500 4.0000

Major

diameter, minimum

2 3

,1111 IIII 1111 IIII IIII IIII

"So hhh ^^ir-;<N <n<no4co cococo^

1

Max. 3

MM IIII IIII IIII IIII IIII

O d r-H^H rt'HrtH <N CM CM CO CO CO CO

Nut

sizes

Pitch d

Min. S

,1111 IIII fill IIII IIII IIII

13d r-irH ^^^^-I n <N <N* <N COCO CO CO

1

Max. 03 illll 1111 1111 IIII IIII IIII

"fjO rl rArArArA (N CM CM CM CO CO CO CO

Minor d

Min. 00 IIII mi Si|| mi mi mi

|d tA -5^r4rH ei«N<N<N cm co coco

Minor

diameter, maximum

>

t- mm mi mi mi iiii iiii |d rl rArA^rl rtCtfCNN CM CO CO CO

1

Min. c© ,1111 IIII IIII IIII IIII IIII

gd rArl rArA^rA CM CM CM <N CO CO CO CO

?I

Pitch d

Max. >c still IIII IIII IIII IIII III!

g O rArA rArA^irA C-i Oi Oi Oi CO CO CO CO

!

i

iiiii mi mi mm mm mm |d rA^A riHHrl cm cm <n cm coco coed

s

Max. OS jllll IIII IIII IIII 1111 IIII

go" rArArA HrirtN CM CM CM CO CO CO CO

Threads per

inch CM

Sizes

aKaS ^JS iSSSfeJ £8?,
18 NATIONAL SCEEW THREAD COMMISSION

«!

ling iiiii urn urn mi

IIIIs §1111 11111 IIIII 1111

IIIII IIIII iiiii 1111

lllli IIIII lllll IIIII 111!

lilil IIIII IIIII §6511 1111

IIIII lllll Ilii! IIIII llll

if

IIIII IIIII HI!! lllll 1111

IIIII IIIII lilli 1111

iiiii IIIII lilil IIIII III!

I

Hill lllll lllll lllli llll

nils mmt mil iiiif mi

11

2322

jjjjj jjjJJ iiiii Mi m
DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS

Itj 2

Jim 11111 mil mil 1111

Major

diameter, minimum

2 iiiiii inn 11111 urn 1111

I1

1

S

sllili §1111 lllls Hill IIII

i

I

1

1

2 jiilii lllll IIIII iiiii III!

1

1

e> sillii lllll IIIII IIIII III!

i 1

00 .iiiii iing mil mil mi

t~ jliiii IIIII lllll IIII! 111!

!

i

iiiiii iiiii gim iiiii mi

i

I

CQ 1

1

jlllll IIIII lllll IIIII ill!

1

.a .iiiii imm inn 11111 mi

•1 M

08 Inches 0.

0600

.0730 .0860 .0990

.

1120

.1250 .1380 .1640 .1900 .2160

.

2500

.3125 .3750 .4375 .5000 .5625 .6250 .7500 .8750

1.0000 1.

1250 1.

2500 1.3750 1.

5000

Threads per

inch gKSSS SXXSS 22233 2223

1

33

jjjjj jjjjj iiiii iiiii ii^i
NATIONAL SCREW THREAD COMMISSION

III

S3 Jim urn urn mil nil

1

Jllll Hill llll Hill

is i 1

,11111 nisi urn mil mi

I

I

t

i

IHII Hill mil liin nil "6© ...... ...... ..... ^.^^

U

• jiiiii nm iiiii mil mi

1

1

- Jim ling iiiii mil mi

Minor

diameter, maximum

i iiiiii iiiii iiiii iiiii mi

3 iim niii mil iiiii mi

•II jinn mm mil iiiii nil

"|'o • • •

• ^^4^

U

i - jinn IS'© ' ' -' mil mil iiiii in "? rH^'FHr^

i - s iin§ iiiii urn iiiii nil

It

i gs^gg sssss sssss 2222

1 iiiii iiiii i i i i i iiiii iiii

iiiii iiiii iiiii i i i i i i i i i

JJJJJ JjjJJ JJiii JjjJJ M
DIMENSIONAL LIMITS OF FASTENING-SCREW THREADS

<

s

e

1

1B

I

Inches 0.

2500

.3125 .3750 .4375 .5000 .5625

.

6250

.7500 .8750 1.

0000 1.

1250 1.

2500 1.3750 1.

5000

minimum

2 a Inches 0.

2500

.3125 .3750 .4375 .5000 .5625 .6250 .7500 .8750 1.

0000 1.

1250 1.

2500 1.3750 1.5000

!

1

i iiili IIIII 1111!

i

i

I i

2 Inches 0.

2268

.2854 .3479 .4050 .4675 .5264 .5889 .7094 .8286 .9536 1.

0709 1.1959 1.

3209 1.

4459

! 1

C5 jiiii IIIII IIIII

i i

3= •Mi §1311 IIIII

fl

t- Inches 0.

2062

.2614 .3239 .3762 .4387 .4943 .5568 .6733 .7874 .9124 1.

0228 1.

1478 1.

2728 1.

3978

si

1

ca Inches 0.

2259

.2845 .3470 .4040 .4665 .5252 .5877 .7082 .8272 .9522 1.

0694 1.

1944 1.

3194 1.

4444

i

i

CO

si Inches 0.

2270

.2857 .3482 .4053 .4678 .5267 .5892 .7098 .8290 .9540 1.

0714 1.

1964 1.

3214 1.

4464

1

i

Inches 0.

2438

.3059 .3684 .4303 .4928 .5543 .6168 .7410 .8652 .9902 1.

1138 1.

2388 1.3638 1.

4888

•1

S3 l

CO Inches 0.

2500

.3125 .3750 .4375 .5000 .5625 .6250 .7500 .8750 1.

0000 1.

1250 1.

2500 1.

3750 1.5000

Threads per

inch

8

bo

jjji JJjjj M

m

ii s ^

it

fl

II!!

11

If II

fl

if 5S

3* 11

II

« If

1111

IP

III

till

piii

11

If

lilt!

m

II is

182129—33 4
42 NATIONAL SCREW THREAD COMMISSION

III III I ! Ill III III 111

|li§ 111 III § I III 111 III III

ipl 111 III I I III III III III

ill! Ill 111 I 1 III 111 III III

III III I i 111 III III III

Ills III III I 1 III III III 111

111 ill I I 111 III 111 111

Ipl II! Ill I I 111 111 III

Ijll ill Hi | i in hi ill

iff ill | | in pi ill

ijii hi iii § § pi pi m

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NATIONAL SCREW THREAD COMMISSION

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48 NATIONAL SCREW THREAD COMMISSION

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50 NATIONAL SCREW THREAD COMMISSION

5. GAGES

The art of measuring screw threads has developed very rapidly

during the past two decades. 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 out 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 l}{ 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. In order that the "not go" gage

may check pitch diameter only, it is necessary that the crest of the

thread be removed so that the major diameter of the plug gage shall never be greater than that specified for the "go" plug gage and the

minor diameter of the ring gage shall never be less than that specified

for the "go" ring gage. A correspondingly greater relief should be

provided at the root of the thread of the "not go" gage than of the

"go" gage. (See "thread form of thread plug and ring gages",

p. 53.)
FUNDAMENTALS OF GAGING SCREW THREADS 51

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

parts to be produced should 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

preceding 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 denned, 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.

Standard designs for certain types of mechanical gages are available

in the report of the American Gage Design Committee, U.S. Department of Commerce Commercial Standard No. CS8-33, "Gage

Blanks." 8 (b) Optical gages.—When gages of the optical type are employed,

the elements of wear and "feel" are not involved, hence no difference

in size between inspection and working gages is necessary, but is desirable.

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

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

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

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

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

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

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

to which adjustable thread-ring gages, thread-snap gages, and other

thread comparators are adjusted for size. In adjusting thread-ring

gages to size, the setting 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 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.

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

gages shall never be outside of the limits specified for the product. All

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

* For sale by the Superintendent of Documents, Government Printing Office, Washington, D.C.
52 NATIONAL SCREW THREAD COMMISSION

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. Temperature at Which Gages Shall be Standard.—The

nominal dimensions of gages and product shall be correct at a temperature of 68° F. {20° C).—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 wearresisting qualities, this condition is ordinarily fulfilled without giving

it special attention.

8. 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 14 to 16 ounces is recommended for pitches finer than 20 threads per inch

and of 2% to 2}£ 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:

1. Classification of Gages, and Gage Tolerances.—Screwthread gages for classes 1,2, and 3 are classified according to accuracy

into classes X, Y, and Z, the class X being the most accurate. Gages

for class 4, close-fit product, are made to smaller tolerances and are designated as class W. 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 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. 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 3, medium fit specifications, class X gages may be required 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.

(6) Class X gages.—Class X gages should be suitable for inspection

and setting gages for classes 1, 2, and 3. The tolerances on these

• Methods of measuring pitch diameter of screw-thread gages are described in appendix 2, p. 129.
GAGE TOLERANCES 53

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 for classes 1, 2, and 3.

(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.

id) 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) Class W gages.—For the inspection of class 4, close-fit product,

gages made within especially close limits are necessary. The toler- ances for such gages, designated as class W, are given in table 21.

(/) Wear on gages.—"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 economy

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.

(g) Tolerances on lead.—The tolerances on lead given in tables 18

to 21, inclusive, are specified as an allowable variation between any

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

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.

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

thread, as specified in tables 18 to 21, 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. Thread Form of Thread Plug and Ring Gages.—The major

diameter of the "go" thread plug gage is the same as the basic major

diameter, with a plus gage tolerance. 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 crest of the thread of the "not go" plug gage is truncated

below the basic major diameter an amount equal to one sixth of the

basic thread depth with a plus gage tolerance. On a basic thread
54 NATIONAL SCREW THREAD COMMISSION

form the corresponding width of flat would be one fourth of the pitch.

On a "not go" plug gage the flat is wider than one fourth of the pitch

by an amount depending upon the product pitch diameter tolerance.

The crest of the thread of the "not go" ring gage is truncated above

the basic minor diameter an amount equal to one third of the basic

thread depth with a minus gage tolerance. On a basic thread form

the corresponding width of flat would be three eighths of the pitch.

On a "not go" ring gage the flat is wider than three eighths of the

pitch by an amount depending upon the product pitch diameter

tolerance. However, adjustable gages, such as thread snap gages,

Figure 18.

Thread form of "go" and "not go" thread plug and ring gages. which may be set to the "not go" limit of any class of fit should have

a width of flat equal to three eighths of the pitch.

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.

Also the effect of angle error on the fit of the "not go" gage with the

product is minimized.

The above requirements are illustrated in figure 18.
GAGE TOLERANCES 55

3. 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 gages given in table 22 may be used.

This table contains recommended tolerances for plain gages, designated as classes X, Y, and Z, which have been tentatively adopted

by the Sectional Committee on the Standardization of Plain Limit

Gages for General Engineering Work. These tolerances are applicable to all classes of product.

4. Recommended Gage Practice.—There are given in table 17

the recommended uses for the foregoing classes of gages. Tables 23,

24, 25, and 26 give limiting dimensions of gages of the several classi- fications for the American National coarse and American National

fine thread series. Table 17.

Recommended uses for classes W, X, Y, and Z "go" thread gages

Class of fit Setting gage Inspection gage Working gage

2 3 4

Class 1, loose fit Class X, table 18 Class Y, table 19 Class Z, table 20. Class Y, table 19. Do.

Class 2, free fit do do

Class 3, medium fit do Class X, table 18 Class 4, close fit.. Class W, table 21 Class W, table 21 Class W, table 21. Note.—"Not go" thread gages for classes 1, 2, and 3 are class X, and for class 4 are class W.
56 NATIONAL SCREW THREAD COMMISSION

Table 18.Tolerances for class X "go" thread gages, and "not go" thread gages

for classes 1, 2, and 8, and all plain gages

Tolerance on pitch diameter 1 Tolerance

in lead 2 Tolerance on half angle of thread

Tolerance on major or minor diameters 1 From

ToFrom

To

2 3 4 5 6 7

Inch Inch Inch Beg. Min. Inch Inch ±

80 u. uuuu u. uuuz 0. 0002 30 u. uuuu U. UUUo 72 .0000 .0002 .0002 30 .0000 .0003

64.. .0000 .0002 . 0002 30 .0000 .0004

56 .0000 .0002 .0002 30 .0000 .0004 48 .0000 .0002 .0002 30 .0000 .0004

44.. .0000 .0002 .0002 20 .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

13. - .0000 .0003 .0003 10 .0000 .0006

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

10 .0000 .0003 .0003 10 .0000 .0006 9 .0000 .0003 .0003 10 .0000 .0007 8 - .0000 .0004 .0004 5 .0000 .0007

7 .0000 .0004 .0004 5 .0000 .0007 6 .0000 .0004 .0004 5 .0000 .0008

5 .0000 .0004 .0004 5 .0000 .0008 4M - — .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.

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. 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 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 3, " Symbols/'

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

coarse-thread series, class 2, free fit, shall be marked 1"—8NC—2. A 1-inch, 14-pitch gage of the American National fine-thread series, class 3, medium fit, shall be marked 1"—14NF—3.
GAGE TOLERANCES 57

Table 19.

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

From— To— From— To—

1 2 3 4 5 6 7

. Inch Inch Inch Beg. Min. Inch Inch ± zh 80 0. 0001 0.0003 0. 0002 Q 40 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 firing

. UUU4

44 .0001 .0004 .0002 30 .0000 .0004 40 .0001 .0004 .0002 30 .0000 .0004

. 0001 . 0004 . 0002 30 . 0000 .0004 32 . 0001 0004 . 0003 20 . 0000 . UUU4

28 . 0002 . 0005 . 0003 20 . 0000 0005

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

. 0002 . 0005 . 0003 20 . 0000 .0005

18 0002 0005 . 0003 15 . 0000 . uuuo

16 . 0002 0006 . 0003 15 . 0000 . uuuo

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

.0003 .0008 .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.

* 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 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 1 From— To— From— To—

2 3 4 5 6 7 Inch Inch Inch Beg. 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 45 .0000 .0004

56. .0002 .0007 .0002 45 .0000 .0004 48 .0002 .0007 .0002 45 .0000 .0004

44 .0002 .0007 .0002 30 .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

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

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

12 .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 4H— - .0007 .0015 .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.

8 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. 182129—33 5
58 NATIONAL SCREW THREAD COMMISSION

Table 21.Tolerances for class W "go" and "not go" thread gages for class 4> close fit

Threads per inch

Tolerance on pitch diameter 1 Tolerance

in lead 2 Tolerance on half angle of thread

Total cu- mulative

tolerance 3

Tolerance on major or minor diameters From

To

prom To

1 2 3 4 5 6 7 8

Inch Inch Inch Beg. Min. Inch Inch Inch ± ±

0. 0000 0. 0001 0. U0015 8 0. UU048 0. 0000 0. 0005 .0000 .0001 . 00015 8 . 00051 .0000 .0005 20 .0000 .0001 . 00015 8 . 00053 .0000 .0005

18 .0000 .0001 . 00015 8 . 00055 .0000 .0005

16 - .0000 .0001 . 00015 8 . 00058 .0000 .0006

14 .0000 . 00015 . 0002 6 . OUUdo .0000 .0006 .0000 . 00015 . 0002 6 . 00070 .0000 .0006 12__ .0000 . 00015 .0002 6 . 00071 .0000 .0006

11 .0000 . 00015 . 0002 6 . 00073 .0000 .0006

10 .0000 .0002 . 00025 5 . 00085 .0000 .0006 9 .0000 .0002 . 00025 5 . 00088 .0000 .0007 8 .0000 .0002 . 00025 5 . 00091 .0000 .0007

7 .0000 . 00025 .0003 4 . 00102 .0000 .0007

6 .0000 . 00025 .0003 4 . 00106 .0000 .0008

5 .0000 . 00025 .0003 4 . 00112 .0000 .0008 m .0000 .0003 .0003 4 .00121 .0000 .0008 4 .0000 .0003 .0003 4 . 00126 .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.

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.

3 The tolerance for one element, namely pitch diameter, lead, or angle, as given above, may be exceeded provided that the errors in the other 2 elements are sufficiently small so that the total cumulative toler- ance shown in column 6 is not exceeded. Table 22.—Tolerances for plain gages 1

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

To- From— To— FromTo—

1 2 3 4 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.

2 All "not go" gages are made to class X tolerances.
DIMENSIONAL LIMITS OF GAGES 59

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NATIONAL SCREW THREAD COMMISSION

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NATIONAL SCREW THREAD COMMISSION

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NATIONAL SCREW THREAD COMMISSION

Threads

per

inch

Inch 0.

8750

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7500

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classes

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68 NATIONAL SCREW THREAD COMMISSION

SECTION IV.—UNIFORM PITCH SCREW-THREAD SERIES

FOR HIGH-PRESSURE FASTENINGS, RAILROAD APPLICATIONS, MACHINERY COMPONENTS, ETC.

1. FORM OF THREAD

The American National form of thread profile as specified in section III shall be used.

2. THREAD SERIES

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 8, 12,

and 16 threads per inch are widely used.

(a) AMERICAN NATIONAL 8-PITCH THREAD SERIES

In table 27 are specified the nominal sizes and basic dimensions of

the " American National 8-pitch thread series.'

Bolts for high-pressure pipe flanges, cylinder-head studs, and similar

fastenings against pressure require that an initial tension be set up

in the fastening, by elastic deformation of the fastening and the components held together, such that the joint will not open up when the

steam or other pressure is applied. To secure a proper initial tension

it is not practicable that the pitch should increase with the diameter

of the thread, as the torque required to assemble the fastening would

be excessive. Accordingly, for such purposes the 8-pitch thread has come into general use.

(b) AMERICAN NATIONAL 12-PITCH THREAD SERIES

The nominal sizes and basic dimensions of the "American National

12-pitch thread series" are specified in table 28. Sizes of 12-pitch threads from one-half inch to and including one and three-fourths 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.

Die-head chasers for sizes up to 3 inches are stocked by manufacturers.10 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 in general use, 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.

(c) AMERICAN NATIONAL 16-PITCH THREAD SERIES

The nominal sizes and basic dimensions of the American National

16-pitch thread series are specified in table 29. The 16-pitch series is a uniform pitch series for such applications

as require a relatively fine thread. It is intended primarily for use on

thread adjusting collars and bearing retaining nuts.

10 See U.S. Department of Commerce Simplified Practice Recommendation R51-29, Die Head Chasers.
UNIFORM PITCH THREAD SERIES 69

3. CLASSIFICATION, TOLERANCES, AND LIMITING DIMENSIONS

The general specifications and classification of fits given in section

V, herein, are applicable to the American National 8-pitch, 12-pitch,

and 16-pitch thread series. The dimensions and tolerances for two

classes of fit derived from tables 35 and 60 are given in tables 30, 31,

and 32. Table 27.

American National 8-pitch thread series

Identification Basic diameters Thread data

Threads

per inch Major

diameter, D

Inches

1. 0000

1. 1250

1. 2500

1. 3750

1. 5000

1. 6250

1. 7500

1. 8750

2. 0000

2. 1250

2. 2500

2. 5000

2. 7500

3. 0000

3. 2500

3. 5000

3. 7500

4. 0000

4. 2500

4. 5000

4. 7500

5. 0000

5. 2500

5. 5000

5. 7500

6. 0000

Pitch

diameter, E

Inches

0. 9188

1. 0438

1. 1888

1. 2938

1. 4188

1. 5438

1. 6688

1. 7938

1.9188

2. 0438

2. 1688

2. 4188

2. 6688

2. 9188

3. 4188

3. 6688

3. 9188

4. 1688

4. 4188

4. 6688

4. 9188

5. 1688

5. 4188

5. 6688

Minor

diameter, K

Metric

equivalent

of major

diameter

Inches

0. 8376

.9626

1. 0876

1. 2126

1. 3376

1. 4626

1. 5876

1.71 26

1. 8376

1. 9626

2. 0876

2. 3376

2. 5876

2. 8376

3. 0876

3. 3376

3. 5876

3. 8376

4. 0876

4. 3376

4. 5876

4. 8376

5. 0876

5. 3376

5. 5876

5. 8376

mm

25. 400

28. 575

31. 750

34. 925

38. 100

41. 275

44. 450

47. 625

50. 800

53. 975

57. 150

63. 500

69. 850

76. 200

82. 550

88. 900

95. 250

101. 600

107. 950

114. 300

120. 650

127. 000

133. 350

139. 700

146. 050

152. 400

Helix angle

at basic pitch diameter,

Beg. Min.

1 Standard size of the American National coarse-thread series. Note.—Pitch, p=0.12500 inch; depth of thread. ft=0.08119 inch; basic width of flat, p/S=0.01562 inch; minimum width of fiat at major diameter of nut, p/24= 0.00521 inch.
70 NATIONAL SCREW THREAD COMMISSION

Table 28.

American National 12-pitch thread series

Identification Basic diameters

Sizes Threads

per inch

• Major

diameter, D

Pitch

diameter, E

Minor

diameter, K

Metric

equivalent

of major

diameter

Helix angle

at basic pitch diameter,

s

Basic area

of section

at root of thread

4

1 2 3 4 5 6 7 8

Square

Inches Inches Inches mm Deg. Mm, inches

12 0. 5000 0. 4459 0. 3917 12. 700 3 24 0. 1205

12 . 5625 . 5084 . 4542 14. 288 2 59 . 1620

12 . 6250 . 5709 . 5167 15. 875 2 40 . 2097

itfe 12 .6875 .6334 .5792 17. 463 2 24 .2635 H— 12 .7500 .6959 .6417 19. 050 2 11 .3234

13//. 1 oLZ . 8125 . 7584 . /U4Z 9A ftQQ ZU. DOO 9 n Z U . ooyo

'/8 12 . 8750 . 8209 . 7667 22. 225 1 51 . 4617

1 K / „ 12 . 9375 . 8834 . 8292 23. 813 1 43 . 5400

1 12 1. 0000 .9459 .8917 25. 400 1 36 .6245 lHe 12 1. 0625 1. 0084 .9542 26. 988 1 30 .7151

1 1.6 2 l'/fc '

1 o 1. 1250 1. 0709 1. 0167 28. 575 1 25 . 8118

lyi 6

1 oIZ 1. 1875 1. 1334 1. 0792 30. 163 1 20 . 9147 11/2*

1 oLZ 1. 2500 1. 1959 1. 1417 31. 750 1 16 1. 0237

15/16 12 1.3125 1. 2584 1. 2042 33. 338 1 12 1. 1389 m 2 12 1. 3750 1. 3209 1. 2667 34. 925 1 9 1. 2602

17/. 1 9IZ 1 AV7K L. 4:610 1. 3834 1. 3292 36. 513 1 6 1. 3876 11^2 1>2 '

1IZ 1. 5000 1. 4459 1. 3917 38. 100 1. 5212 m. 12 1. 6250 1. 5709 1. 5167 41. 275 58 1. 8067 i% 12 1. 7500 1. 6959 1. 6417 44. 450 54 2. 1168

1 7J, IZ 1. 8750 1. 8209 1. 7667 47. 625 50 2. 4514

2

1 9IZ Z. UUUU 1. 9459 1. 8917 50. 800 47 2. 8106 2H 12 2. 2500 2. 1959 2. 1417 57. 150 42 3. 6025

2fc 12 2. 5000 2. 4459 2. 3917 63. 500 37 4. 4927

z°,% 1 9IZ 2. 7500 2. 6959 2. 6417 69. 850 34 5. 4810

Q 1 9IZ 6. UUUU 2. 9459 2. 8917 76. 200 31 6. 5674

334 12 3. 2500 3. 1959 3. 1417 82. 550 29 7. 7521

12 3. 5000 3. 4459 3. 3917 88. 900 26 9 0349 3M 12 3. 7500 3. 6959 3. 6417 95. 250 25 10! 4159

4 12 4. 0000 3. 9459 3. 8917 101. 600 23 11. 8951

12 4. 2500 4. 1959 4. 1417 107. 950 22 13. 4725 m 12 4. 5000 4. 4459 4. 3917 114. 300 21 15. 1480 m . 12 4. 7500 4. 6959 4. 6417 120. 650 19 16. 9217

5 12 5. 0000 4. 9459 4. 8917 127. 000 18 18. 7936 5H 12 5. 2500 5. 1959 5. 1417 133. 350 18 20. 7636 5H 12 5. 5000 5. 4459 5. 3917 139. 700 17 22. 8319 m~ 12 5. 7500 5. 6959 5. 6417 146. 050 16 24. 9983

6 12 6. 0000 5. 9459 5. 8917 152. 400 15 27. 2628

Thread data

1 Standard size of the American National coarse-thread series.

2 Standard size of the American National fine-thread series. Note.—Pitch, p=0.08333 inch; depth of thread, ft=0.05413 inch; basic width of flat, p/8=0.01042 inch; minimum width of flat at major diameter of nut, p/24 =0.00347 inch.
UNIFORM PITCH THREAD SERIES

Table 29.American National 16-pitch thread series 71

Identification Basic diameters

Sizes Threads

per inch Major

diameter, D

Pitch

diameter, E

Minor

diameter, K

IVTstric of m&jor

Helix angle

at basic pitch diameter,

*

-L>doil/ alcd

Ul oCL-LlUUl

£\t CL U 7*nnt IUUU nfUi. bin cauf ttK 2 4

2 3 4 5 6 7 8

Square

Inches Inches Inches nun Beg. Min. inches % 1 16 0. 7500 0. 7094 0. 6688 19. 050 36 0. 3513

J6 16 .8750 .8344 .7938 22. 225 22 .4949

1 16 1. 0000 .9594 .9188 25. 400 11 .6630 m 16 1. 1250 1. 0844 1. 0438 28. 575 3 .8557 1H 16 1,2500 1. 2094 1. 1688 31. 750 57 1. 0729 m 16 1. 3750 1. 3344 1.2938 34. 925 51 1. 3147 m 16 1. 5000 1. 4594 1. 4188 38. 100 47 1. 5810 i% . 16 1. 6250 1. 5844 1. 5438 41. 275 43 1. 8719 i% 16 1. 7500 1. 7094 1. 6688 44. 450 40 2. 1873 i% 16 1. 8750 1. 8344 1. 7938 47. 625 37 2. 5272 2 iID 1 9594 1 Q1 SQ ou. ouu 35 2H 16 2. 1250 2. 0844 2. 0438 53. 975 33 3. 2807 2H 16 2. 2500 2. 2094 2. 1688 57. 150 31 3. 6943

2YL 16 2. 5000 2. 4594 2. 4188 63. 500 28 4. 5950 2U 16 2. 7500 2. 7094 2. 6688 69. 850 25 5. 5940

3 16 3. 0000 2. 9594 2. 9188 76. 200 23 6. 6911 m 16 3. 2500 3. 2094 3. 1688 82. 550 21 7. 8864 3^ 16 3. 5000 3. 4594 3. 4188 88. 900 20 9. 1799

33/4 16 3. 7500 3. 7094 3. 6688 95. 250 18 10. 5715

4 16 4. 0000 3. 9594 3. 9188 101. 600 17 12. 0614

Thread data

1 Standard size of the American National fine-thread series. Note.—Pitch, p=0.06250 inch; depth of thread, /i = 0.04059 inch; basic width of flat, minimum width of flat at major diameter of nut, p/24=0.00260 inch. Table 30.

Limiting dimensions and tolerances, classes National 8-pitch thread series

0.00781 inch; and 8 fits, American

Dimensions and tolerances 1 Size (inches) 12 Bolts and Sckews

Classes 2 and 3, major diame-j^-1^

"

ter 1to1-"I

Classes 2 and 3, minor diameter. Max.3 . Class 2, pitch diameter (forfJJ??--

general use)

j ^ "

{Max.. Min .

Tol...

Ntjts and Tapped Holes

Classes 2 and 3, major diameter Min.4 .. Classes 2 and 3, minor diame-j^^- - ter

ItoI.".".: Classes 2 and 3, pitch diameter Min...

Class 2, pitch diameter (forfMax.5 .. general use) \Tol

Class 3, pitch diameter {toP'

5 "

Inch

1. 0000

.9848 .0152

Inches

1. 1250

1. 1098 .0152

.9716

.9188 1.0438

,9112| 1.0359

. 0076 . 00'

,9134

,0054

1. 0000

.8647

.8795

.0148

.9188

.9264

.0076 .9242

.0054

1. 0438

1. 0383 .0055

1. 1250 .9897

1. 0032

.0135

1. 0438

1. 0517

.0079

1. 0493

.0055

Inches

1. 2500

1. 2348 .0152

1.0

1. 1688

1. 1605

.0083

1. 1688

1. 1630 .0058

1. 2500

1. 1147

1. 1282 .0135

1. 1688

1. 1771

.0083

1. 1746 .0058

Inches

1. 3750

1. 3598 .0152

1. 2216

1. 2938

1. 2852

.0086

1. 2938

1. 2877

.0061

1. 3750

1. 2397

1. 2532

.0135

1. 2938

1. 3024

.0086

1. 2999

.0061

Inches

1. 5000

1. 4848 .0152

1. 3466

1.41

1. 4098

.0090

1. 4188

1.4125 .0063

1. 5000

1. 3647

1. 3782

.0135

1. 4188

1.42 .0090

1. 4251

.0063

Inches

1. 6250

1.6.0152

1. 4716

1. 5438

1. 5345

.0093

1. 5438

1. 5373

.0065

1. 6250

1. 4897

1. 5032 .0135

1. 5438

1. 5531 .0093

1. 5503 .0065

Inches

1. 7500

1. 7348 .0152

1.5

1.6

1. 6591

.0097

1. 668S

1. 662C .0068

1. 7500

1. 6147

1. 6282

.0135

1. 6785

.0097

1. 6756

.0068 Footnotes at end of table.
72 NATIONAL SCEEW THREAD COMMISSION

Table 30.

Limiting dimensions and tolerances, classes 2 and 8 fits, American

National 8-pitch thread series—Continued

Dimensions and tolerances

Bolts and Screws

Classes 2 and 3, major diame-j]^a* "

ter 1to1_"_"

Classes 2 and 3, minor diameter Max.s„

Class 2, pitch diameter (for [Max...

general use) {Min

LTol.-- {Max... Min

Tol Nuts and Tapped Holes

Classes 2 and 3, major diameter Min.4 .. Classes 2 and 3, minor diame- "

ter ItoI.I"

Classes 2 and 3, pitch diameter Min

Class 2, pitch diameter (forfMax.s..

general use) \Tol

Class 3, pitch diameter {toI*

Size (inches) m 2U 2H 2%

Inches

2. 12501

2. 1098 .0152

1. 9716

2. 0438

2. 0331 .0107

2. 0438

2. 0363 .0075

2. 1250

1. 9897

2. 0032 .0135

2. 0438

2. 0545

.0107

2. 0513

.0075

Inches

2. 2500

2. 2348 .0152

2. 0966

2. 1688

2. 1578 .0110

2. 1688

2. 1611 .0077

2. 2500

2. 1147

2. 1282 .0135

2. 1688

2. 1798 .0110

2. 1765 .0077

Inches

2. 5000

2. 4848 .0152

2. 4188

2. 4071 .0117

2. 4188

2. 4106 .0082

2. 5000

2. 3647

2. 3782 .0135

2. 4188

2. 4305 .0117

2. 4270 .0082

Inches

2. 7500

2. 7348 .0152

2. 5966

2. 6688

2. 6564 .0124

2. 6688

2. 6601 .0087

2. 7500

2. 6147

2. 6282

.0135

2. 6812 .0124

2. 6775 .0087

Inches

3. 0000

2. 9848 .0152

2. 8466

2. 9188

2. 9058 .0130

2. 9188

2. 9096 .0092

3. 0000

2. 8647

2. 8782

.0135

2. 9188

2. 9318

.0130

2. 9280

.0092

3H 3}^ 3%

Inches

3. 2500

3. 2348 .0152

3. 0966

3. 1688

3. 1556 .0132

3. 1688

3. 1595 .0093

3. 2500

3. 1147

3. 1282 .0135

3. 1688

3. 1820 .0132

3. 1781 .0093

Inches

3. 5000

3.4! .0152

3. 3466

3. 4188

3. 4055

.0133

3. 4188

3. 4095

.0093

3. 5000

3. 3647

3. 3782

.0135

3. 4188

3. 4321

.0133

3. 4281 .0093

Inches

3. 7500

3. 7348 .0152

3. 6554 .0134

3. 6688

3. 6594 .0094

3. 7500

3. 6147

3. 6282 .0135

3. 6822

.0134

3. 6782

.0094

Inches

4. 0000

3. 9848 .0152

3. 9188

3. 9053

.0135

3. 9188

3. 9093

.0095

4. 0000

3. 8647

3. 8782

.0135

3. 9188

3. 9323 .0135

3. 9283 .0095

Dimensions and tolerances Bolts and Screws

use).

Nuts and Tapped Holes

Size (inches) 4M 5 6 (Max.. {Min—

[Tol__.

Inches

4. 2500

4. 2348 .0152

Inches

4. 5000

4. 4848 .0152

Inches

4. 7500

4. 7348

.0152

Inches

5. 0000

4. 9848 .0152

Inches

5. 2500

5. 2348 .0152

Inches

5. 5000

5. 4848 .0152

Inches

5. 7500

5. 7348 .0152

Inches

6. 0000

5. 9848 .0152 Max.3. 4. 0966 4. 3466 4. 5966 4. 8466 5. 0966 5. 3466 5. 5966 5. 8466 [Max. . ^Min...

"lTol__.

4. 1688

4. 1551 .0137

4. 4188

4. 4050

.0138

4. 6688

4. 6549 .0139

4. 9188

4. 9048

.0140

5. 1688

5. 1547 .0141

5. 4188

5. 4046

.0142

5. 6688

5. 6545 .0143

5. 9188

5. 9044 .0144 (Max.. .{Min—

iTol...

4. 1688

4. 1592 .0096

4. 4188

4. 4091 .0097

4. 6688

4. 6590

.0098

4. 9188

4. 9089 .0099

5. 1688

5. 1589 .0099

5. 4188

5. 4088

.0100

5. 6688

5. 6587

.0101

5. 9188

5. 9086

.0102

Min.4 . 4. 2500 4. 5000 4. 7500 5. 0000 5. 2500 5. 5000 5. 7500 6. 0000 (Min... {Max..

iTol...

4. 1147

4. 1282 .0135

4. 3647

4. 3782

.0135

4. 6147

4. 6282

.0135

4. 8647

4. 8782

.0135

5. 1147

5. 1282 .0135

5. 3647

5. 3782

.0135

5. 6147

5. 6282

.0135

5. 8647

5. 8782

.0135 Min 4. 1688 4. 4188 4. 6688 4. 9188 5. 1688 5. 4188 5. 6688 5. 9188 /Max.5

. \Tol-_.

4. 1825 .01374. 4326

.0138

4. 6827 .01394. 9328

.0140

5. 1829 .01415. 4330

.0142

5. 6831 .0143

5. 9332

.0144 /Max.s. -\Tol--.

4. 1784 .00964. 4285 .0097

4. 6786

.0098

4. 9287

.0099

5. 1787 .0099

5. 4288

.0100

5. 6789 .0101

5. 9290

.0102

1 Pitch diameter tolerances include errors of lead and angle. The class 2 tolerances are based on the

formulas in table 60 and a length of engagement equal to the basic major diameter for sizes from 1}4 to 3 inches, inclusive, and a length of engagement of 3 inches for sizes over the 3-inch. The class 3 tolerances

are 70 percent of the class 2 tolerances. The 1-inch size being in the American National coarse-thread series, the tolerances for this size correspond to that series.

2 Standard size screw and nut of the American National coarse-thread series.

3 Dimensions given for the maximum minor diameter of the screw are figured to the intersection of the worn tool arc with a center line through crest and root. The minimum minor diameter of the screw shall be that corresponding to a flat at the minor diameter of the minimum screw equal to X P, and may be

determined by subtracting 0.0812 inch from the minimum pitch diameter of the screw.

4 Dimensions for the minimum major diameter of the nut correspond to the basic flat X p), and the

profile at the major diameter produced by a worn tool must not fall below the basic outline. The maxi- mum major diameter of the nut shall be that corresponding to a flat at the major diameter of the maximum

nut equal to WiXp, and may be determined by adding 0.0992 inch to the maximum pitch diameter of the nut.

* These dimensions are the minimum metal or "not go" size. The "go" or basic size is the one that should be placed on the component drawing with the tolerance.
UNIFORM PITCH THREAD SERIES 73

Table 31.

Limiting dimensions and tolerances, classes 2 and 3 fits, American

National 12-pitch thread series

Dimensions and tolerances 1 Size (inches) Ha 1M6

Bolts and Screws {Max

Min.

Tol...

Classes 2 and 3, minor diameter. Max. *.

Class 2, pitch diameter (for gen- J^ffjf

"~ eral use)

I To?""

[Max..

Class 3, pitch diameter ^Min.._ ITol—

Nuts and Tapped Holes

Classes 2 and 3, major diameter. Min.

(Min...

Classes 2 and 3, minor diameter. { Max.. ITol—

Classes 2 and 3, pitch diameter.. Min„.

Class 2, pitch diameter ("Max. 8. (for general use) \Tol...

Class 3, pitch diameter {toI**

*~

Inch

0. 5000 4888 0112

3978

.4459

,4403 ,0056

,4459 4419 0040

5000

,4225 ,0127 4459 4515

,0056 4499 0040

Inch

0. 5625

5513 0112

4603

.5028

.0056

.5084 .5044

.0040

.5625

.4723 .4850

.0127

.5084

.5140 .0056 .5124

.0040

Inch

0. 6250 .613

.0112

.5228 .5709

.5653 .0056 .5709

.5869 .0040

.6250

.5348

.5438

. 0090

,5765

,0056 .5749

.0040

Inch

0. 6875 6763 0112

5853 6334

6278

0056 6334

6294

0040

.6875

.5973

,6063 0090

,6334 6390

0056

6374 0040

Inch

0. 7500

7388 0112

6478

0056

.0040

.7500

0090

7015 0056

.0040

Inch

0. 8125

.8013 .0112

.7103 .7584

.7528

.0056 .7584

.7544

.0040

.8125

.7223

.7313 .0090 .7584

.7640

.0056 .7624

.0040

Inch

0. 8750

8638

0112

7728

8209

,8153 0056

8209

8169

0040

8750

.7938

. 0090

,8265

,0056

,8249 ,0040

Inch

0. 9375

.9263 .0112

.8353 ,8834

.8778 .0056 .8834

,8794

,0040

.9375

, 8473

.8583 0090

8834

0056 8874

0040

Inch

1. 0000

.9888 .0112

.8978

.9459

.9403 .0056

.9459

.9419 .0040

1. 0000

9188

0090

9459 9515

0056

0040

Inches

1. 0625

1. 0513 .0112

.9603

1. 0084

1. 0028

.0056

1. 0084

1. 0044

.0040

1.0625 .9723

.9813 .0090

1.0084

1. 0140

.0056

1. 0124 .0040

Dimensions and tolerances 1

Bolts and Screws

Classes 2 and 3, major diame- I^f^"

ter ]to1-~_" Classes 2 and 3, minor diameter Max. 4. Class 2, pitch diameter (forJMf*--

general use) [To\_"' (Max..

Class 3, pitch diameter ^Min.._

|To1._. Nuts and Tapped Holes

Classes 2 and 3, major diameter Min. fi . Classes 2 and 3, minor diame1

ter"" ItoI-11

Classes 2 and 3, pitch diameter Min...

Class 2, pitch diameter (for f Max. 6 . general use) \Tol _ _

.

Class 3, pitch diameter {to?*''"

Size (inches) 1H 3 lHe 1J4 3 1Mb 1% 3 l

7Aa IY2 3 IH 1U

Inches

1. 1250

1. 1138 .0112

1. 0228

1. 0709

1. 0653

.0056

1. 0709

1..0040

1. 1250

1. 0348

1. 0438 .0090

1. 0709

1. 0765 .0056

1. 0749

.0040

Inches

1. 1875

1. 1763 .0112

1. 0853

1. 1334

1. 1278 .0056

1. 1334

1. 1294 .0040

1. 1875

1.0

1. 1063 .0090

1. 1334

1. 1390 .0056

1. 1374 .0040

Inches

1. 2500

1. 2388 .0112

1. 1478

1. 1959

1. 1903 .0056

1. 1959

1. 1919 .0040

1. 2500

1. 1598

1. 1688

1. 1959

1. 2015 .0056

1. 1999 .0040

Inches

1.3125

1. 3013 .0112

1. 2103

1. 2584

1. 2528 .0056

1. 2584

1. 2544

.0040

1. 312;

1. 2223

1. 2313 .0090

1. 2584

1. 2640 .0056

1.2624 .0040

Inches

1. 3750

1. 3638 .0112

1.2728

1. 3209 1.3153 .0056

1.3209

1. 3169 .0040

1. 3750

1. 2848

1. 2938

1. 3209

1. 3265 .0056

1. 3249

Inches

1. 4375

1. 4263 .0112

1. 3353

1. 3834

1. 3778 .0056

1. 3834

1. 3794

.0040

1. 4375

1. 3473

1. 3563

1. 3834

1. 3890

.0056

1. 3874 .0040

Inches

1. 5000

1.4.0112

1. 3978

1. 4459

1. 4403 .00&

1. 4459

1.4419 .0040

1. 5000

1.4i

1. 4188

.0090

1. 4459

1. 4515

.0056

1. 4499 .0040

Inches

1. 6250

1. 6138 .0112

1.5228

1. 5709

1. 5645 .0064

1. 5709

1. 5664 .0045

1.6250

1. 5348

1. 5438

1. 5709

1. 5773 .0064

1. 5754 .0045

Inches

1. 7500

1. 7388 .0112

1. 6478

1. 6959

1. 6894 .0065

1. 6959

1. 6913 .0046

1. 7500

1. 6598

1. 6688

.0090

1.7024 .0065

1.7005

Footnotes at end of table. 182129—33 6
74 NATIONAL SCREW THREAD COMMISSION

Table 31.

Limiting dimensions and tolerances, classes 2 and 8 fits, American

National 12-pitch thread series—Continued

Dimensions and tolerances

Bolts and Screws

[Max_.

Classes 2 and 3, major diameter -iMin... |ToL__

Classes 2 and 3, minor diameter Max. 4 . {Max..

Min...

Tol... (Max..

Class 3, pitch diameter ^Min...

iTol... Nuts and Tapped Holes

Classes 2 and 3, major diameter MinA

[Min...

Classes 2 and 3, minor diameter { Max.

iTol...

Classes 2 and 3, pitch diameter Min... {Max 6 Tol

" {Max 6 Tol ' "

Size (inches)

In

1. 8750

1. 8638 .0112

1. 7728

1. 8209

1. 8143 .0066

1. 8209

1. 8163

.0046

1. 8750

1. 7848

1. 7938

1. 8209

1. 8275

1. 8255 .0046

In

2. 0000

1. 91 .0112

1. 8978

1. 9459

1. 9392

.0067

1. 9459

1. 9412

.0047

2. 0000

1.9i 1.9.0090

1. 9459

1. 9526

.0067

1. 9506

.0047

2J4 2Y2 2Vi

In.

2. 2500

2. 2388 .0112

2. 1478

2. 1959

2. 1890 .0069

2. 1959

2. 1911 .0048

2. 2500

2.

2. 1688 .0090

2. 1959

2. 2028

. 0069

2. 2007 .0048

In.

2. 5000

2. 4888 .0112

2. 3978

2. 4459

2. 4388

.0071

2. 4459

2. 4410

.0049

2. 5000

2. 4098

2. 4188 .0090

2. 4459

2. 4530

.0071

2. 4508

.0049

In.

2. 7500

2. 7388 .0112

2. 6478

2. 6959

2. 6887 .0072

2. 6959

2. 6909

. 0050

2. 7500

0090

6959

7031

,0072

.7009

,0050

In.

3. 0000

2. 9888

.0112

2. 8978

2. 9459

2. 9385 .0074

2. 9459

2. 9408

.0051

3. 0000

0090

9459

9533 0074

9510

0051

31/4 3^

In.

3. 2500

3. 2388 .0112

3. 1478

3. 1959

3. 1884 .0075

3. 1959

3. 1907 .0052

2500

1598

1688 0090

1959 2034

,0075

,2011 ,0052

In.

3. 5000

3. 4.0112

3. 3978

3. 4459

3. 4383 .0076

3. 4459

3. 4406

.0053

3. 5000

4188 0090

4459

4535 0076

4512

00

In.

3. 7500

3. 7388 .0112

3. 6478

3. 6959

3. 6881 .0078

3. 6959

3. 6905 .0054

3. 7500

3. 6598

3. 6688 .0090

3. 6959

3. 7037

.0078

3. 7013 .0054

Siz8 Dimensions and tolerances 1 4 41/2 5 5}/2 6

Bolts and Screws

Classes 2 and 3, major diameter • Max...

Min....

Tol....

In.

4. 0000

3. 9888 .0112

In.

4. 2500

4. 2388 .0112

In.

4. 5000

4. 4888 .0112

In.

4. 7500

4. 7388 .0112

In.

5. 0000

4. 9888 .0112

In.

5. 2500

5. 2388 .0112

In.

5. 5000

5. 4888

.0112

In.

5. 7500

5. 7388 .0112

In.

6. 0000

5. 9888 .0112 Classes 2 and 3. minor diameter Max. 4 3. 8978 4. 1478 4. 3978 4. 6478 4. 8978 5. 1478 5. 3978 5. 6478 5. 8978 [Max...

Class 2, pitch diameter (for general useK Min

iTol....

3. 9459

3. 9380

.0079

4. 1959

4. 1879 .0080

4. 4459

4. 4378

.0081

4. 6959

4. 6876

.0083

4. 9459

4. 9375

.0084

5. 1959

5. 1874 .0085

5. 4459

5. 4373 .0086

5. 6959

5. 6872

.0087

5. 9459

5. 9371 .0088 Class 3, pitch diameter - Max...

Min....

Tol....

3. 9459

3. 9404

.0055

4. 1959

4. 1903

.0056

4. 4459

4. 4402

.0057

4. 6959

4. 6901 .0058

4. 9459

4. 9400

.0059

5. 1959

5. 1900 .0059

5. 4459

5. 4399 .0060

5. 6959

5. 6898

.0061

5. 9459

5. 9397

.0062 Nuts and Tapped Holes

Classes 2 and 3, major diameter .Min. 5 .. 4. 0000 4. 2500 4. 5000 4. 7500 5. 0000 5. 2500 5. 5000 5. 7500 6. 0000 Classes 2 and 3, minor diameter • Min.... Max...

Tol

3. 9098

3. 9188 .0090

4. 1598

4. 1688 .0090

4. 4098

4. 4188

.0090

4. 6598

4. 6688

.0090

4. 9098

4. 9188 .0090

5. 1598

5. 1688 .0090

5. 4098

5. 4188 .0090

5. 6598

5. 6688 .0090

5. 9098

5. 9188 .0090 Classes 2 and 3, pitch diameter .Min 3. 9459 4. 1959 4. 4459 4. 6959 4. 9459 5. 1959 5. 4459 5. 6959 5. 9459 Class 2, pitch diameter (for general use) fMax.e..

ITol....

3. 9538 .00794. 2039 .00804. 4540

.0081

4. 7042

.0083

4. 9543 .0084

5. 2044 .00855. 4545

.0086

5. 7046

.0087

5. 9547 .0088 Class 3, pitch diameter fMax. 6 .. (Tol

3. 9514

.0055

4. 2015 .0056

4. 4516

.0057

4. 7017 .00584. 9518

.0059

5. 2018 .00595. 4519 .00605. 7020

.0061

5. 9521 .0062

1 Pitch diameter tolerances include errors of lead and angle. The class 2 tolerances for sizes above 1^2 inches are based on the formulas in table 60 and a length of engagement of 6 threads or H inch. The class

3 tolerances are 70 percent of the class 2 tolerances. For lengths of engagement of 1 inch, 0.0010 inch may

be added to these tolerances. As certain sizes up to \Vi inches are included in the American National

coarse or fine thread series, the tolerances to and including \Yi inches correspond to those series.

2 Standard size screw and nut of the American National coarse thread series.

3 Standard size screw and nut of the American National fine thread series.

4 Dimensions given for the maximum minor diameter of the screw are figured to the intersection of the worn tool arc with a center line through crest and root. The minimum minor diameter of the screw shall be that corresponding to a flat at the minor diameter of the minimum screw equal to HXp, and may

be determined by subtracting 0.0541 inch from the minimum pitch diameter of the screw.

5 Dimensions for the minimum major diameter of the nut correspond to the basic flat, (HXp), 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 nut shall be that corresponding to a flat at the major diameter of the maximum nut equal to VuXv, and may be determined by adding 0.0662 inch to the maximum pitch diameter of the nut.

6 These dimensions are the minimum metal or "not go" size. The "go" or basic size is the one that should be placed on the component drawing with the tolerance.
UNIFORM PITCH THREAD SERIES 75

Table 32.

Limiting dimensions and tolerances, class 3 fit, American National

16-pitch thread series

Size (inches) Dimensions and tolerances 1 % 2 7A 1 m in m m 13/4 m

Bolts and Screws

Major diameter (Max...{Min....

lTol____

In.

0. 7500 ^7410

.0090

In.

0. 875C !8660 .0090

In.

1. 0000

.' 9910

.0090

Ins.

1. 125C L 1160 .0090

Ins.

1. 2500

1. 2410

.0090

Ins.

1. 3750

1. 3660 .0090

Ins.

1. 500C L4910

.0090

Ins.

1. 625C

l! 6160

.0090

Ins.

1. 7500

1. 7410 .0090

Ins.

1. 8750

l'. 8660

.0090 Minor diameter _Max.3__ .6733 .7983 .9233 1. 0483 1. 1733 1. 2983 1. 4233 1. 5483 1. 6733 1. 7983

Pitch diameter (Max...

Min.__. [Tol—.

. 7094 !7062 .0032. 8344

!8308

.0036

. 9594

!9557

.0037

1. 0844

1. 0806 .0038

1. 2094

1. 2056 .0038

1. 3344

1. 3305 .0039

1. 4594 L 4554

.0040

1. 5844 L 5803

.0041

1. 7094

1. 7053

.0041

1. 8344 L 8302

.0042 Nuts and Tapped Holes

Major diameter Min.4 .. .7500 .8750 1. 0000 1. 1250 1. 2500 1. 3750 1. 5000 1. 6250 1. 7500 1. 8750 Minor diameter

(Min.... Max...

[Tol

. 6823

6993 !o080

. 8073

8141 !0068

.9323

. 9391 !0068

1. 0573

1. 0641 !0068

1. 1823

1. 1891 .0068

1. 3073

1.3141 .0068

1. 4323

1 4391 !0068

1. 5573

1 5641 !0068

1. 6823

1 6891 !0068

1. 8073

1 81/11 .0068

Pitch diameter

[Min....

'.Max...

[Tol....

.7094

.7126 .0032

.8344 .8380

.0036

.9594

.9631 .0037

1. 0844

1. 0882 .0038

1. 2094

1. 2132 .0038

1. 3344

1. 3383 .0039

1. 4594

1. 4634

.0040

1. 5844

1. 5885 .0041

1. 7094

1. 7135

.0041

1. 8344

1. 8386 .0042

Size (inches) Dimensions and tolerances 1 2 •m 2H 2H 2% 3 3H 324 4

Bolts and Screws

Major diameter (Max... Min.—

[Tol....

Inches 1.9910

. 0090

Inches

2. 1250

2. 1160

. 0090

Inches

2. 2500

2. 2410

. 0090

Inches

2. 5000

2. 4910

. 0090

Inches

2. 7500

2. 7410 .0090

Inches

3. 0000

2. 9910

.0090

Inches

3. 2500

3! 2410

. 0090

Inches

3. 5000 3^4910

. 0090

Inches

3. 7500

3! 7410

. 0090

Inches

4. 0000

3! 9910

. 0090 Minor diameter _._ .Max.s.. 1. 9233 2. 0483 2. 1733 2. 4233 2. 6733 2. 9233 3. 1733 3. 4233 3. 6733 3. 9233

Pitch diameter (Max...

Min....

[Tol....

1. 9594

l! 9551 .0043

2. 0844

2. 0801 .0043

2. 2094

2. 2050 .0044

2. 4594

2. 4549 .0045

2. 7094

2. 7048 .0046

2. 9594

2. 9547 .0047

3. 2094

i. 2046 .0048

3. 4594

i. 4545

.0049

3. 7094

3! 7044 .0050

3. 9594

3! 9543

.0051 Nuts and Tapped Holes

Major diameter .Min.4 .. 2. 0000 2. 1250 2. 2500 2. 5000 2. 7500 3. 0000 3. 2500 3. 5000 3. 7500 4. 0000 Minor diameter

(Min.... Max...

Tol....

1. 9323

1. 9391 .0068

2. 0573

2. 0641 .0068

2. 1823

2. 1891 .0068

2. 4323

2. 4391 .0068

2. 6823

2. 6891 .0068

2. 9323

2. 9391 .0068

3. 1823

3. 1891 .0068

3. 4323

3. 4391 .0068

3. 6823

3. 6891 .0068

3. 9323

3. 9391 .0068

Pitch diameter Min.... Max...

Tol

1. 9594

1. 9637

.0043

2. 0844

2. 0887 .0043

2. 2094

2. 2138 .0044

2. 4594

2. 4639

.0045

2. 7094

2. 7140 .0046

2. 9594

2. 9641 .0047

3. 2094

3. 2142

.0048

3. 4594

3. 4643

.0049

3. 7094 3.7144

.0050

3. 9594

3. 9545

.0051

1 Pitch diameter tolerances include errors of lead and angle, and are 70 percent of the tolerances for class 2 based on the formulas in table 60 and a length of engagement of 6 threads or % inch. The f-i-inch size being in the American National fine-thread series, the tolerance for this size corresponds to that series.

2 Standard size screw and nut of the American National fine-thread series.

3 Dimensions given for the maximum minor diameter of the screw are figured to the intersection of the

worn-tool arc with a center line through crest and root. The minimum minoi diameter of the screw shall be that corresponding to a fiat at the minor diameter of the minimum screw equal to lAXp, and may be

determined by subtracting 0.0406 inch from the minimum pitch diameter of the screw.

4 Dimensions for the minimum major diameter of the nut correspond to the basic flat (AXp) 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 nut shall be that corresponding to a flat at the major diameter of the maximum nut

equal to YaXp, and may be determined by adding 0.0496 inch to the maximum pitch diameter of the nut.

4. GAGES

The specifications for gages given in section III are applicable

to the American National 8-, 12-, and 16-pitch thread series. Toler- ances on diameter, lead, and angle for classes W, X, Y, and Z gages,

as specified in section III, are given in table 33.
76 NATIONAL SCREW THREAD COMMISSION

Each gage shall be marked for identification, with the diameter,

pitch, and class of fit as specified in section II, division 3, " Symbols. ,; Table 33.

Tolerances for thread gages, American National 8-, 12-, and 16-pitch thread series 8-PITCH

Class of gage

Tolerance on pitch diameter 1 Tolerance on lead 2 Tolerance on half angle of threadTolerance on major or minor diameters 1 From

To— From

To—

Class W

Class X and "not go"

Class Y

Class Z

Inch

0. 0000 .0000

.0002

.0005

Inch

0. 0002

.0004 .0007

.0013

Inch

0. 00025

.0004 .0004

.0005

Beg. Min.

5

5

5

5

Inch

0. 0000

.0000

.0000 .0000

Inch

0. 0007 .0007

.0007

.0007 12-PITCH

Class W

Class X and "not go"

Class Y

Class Z

0. 0000

.0000 .0002

.0004

0. 00015

.0003 .0005

.0011

0. 0002

.0003

.0003 .0004

610

10

10

0. 0000

.0000 .0000

.0000

0. 0006

.0006 .0006

.0006 16-PITCH

Class W

Class X and "not go"

Class Y

Class Z

0. 0000

.0000 .0002

.0004

0. 0001 .0003

.0006

.0010

0. 00015

.0003

.0003 .0004

8

10

15

15

0. 0000

.0000

.0000 .0000

0. 0006

.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 standard length of engage- ment. SECTION V. 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% diameters.

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.

1. FORM OF THREAD

The American National form of thread profile as specified in

section III shall be used.

2. THREAD SERIES

In section IV there are given the limiting dimensions for an 8-pitch, a 12-pitch, and a 16-pitch thread series. The use of these series,
SPECIAL THREADS 77

wherever possible, is recommended for all applications requiring

other than American National coarse or fine threads.

Whenever sizes and pitches in the American National coarse or

fine, or the 8-, 12-, or 16-pitch thread series are not suitable, it is recommended that one of the following pitches be selected: 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 34.

3. CLASSIFICATION AND TOLERANCES

There are established herein for general use four classes of screwthread 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, nor in the 8-, 12-, or 16-pitch thread series. Table 34.

Thread data for recommended pitches for special threads

Threads per inch, n Pitch, h Depth of thread, p

Basic width

of flat, p/8

64

.

56. 48.

40.

36.

32.

28. 24

201816

14

12

108.

6..

4..

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

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 classes 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. 11

11 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.
78 NATIONAL SCREW THREAD COMMISSION

2. Tolerances.12—(a) The tolerances specified represent the

extreme variations allowed 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 all errors of pitch diameter,

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

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

(/) 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. 81.)

(g) 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 (}iXp) 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.

(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 (^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.

(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 2 Recommendations and explanations regarding the application of tolerances are given in appendix 1, p. 127.
SPECIAL THREADS 79

(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. 13

(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. 14 Tables 35 and 36 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 has no allowance and the

tolerances are smaller.

Tables 35 and 37 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 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 members. It is the same as class 2 in every particular except that the tolerances are

smaller.

Tables 35 and 38 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, gages made to special toler- ances for this class (see table 21, p. 58), 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.

13 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 11, p. 77.
80 NATIONAL SCREW THREAD COMMISSION

The maximum pitch diameters of the screws are slightly larger

than the minimum pitch diameters of the nuts determined from

table 35. Tables 35 and 39 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 35, 36, 37, 38, and 39 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 35. Pitch diameter tolerances are taken from tables 36, 37, 38, or 39,

depending upon the class of fit required. These pitch diameter toler- ances were obtained by adding increments 15 corresponding to the

major diameters at the top, the threads per inch at the side of the

table, and mean lengths of engagement of }i, 1, and 2}i inches for

pitches from 64 to 12 threads per inch, inclusive, and y2 , 2, and 4%

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 greater or 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 difficulties in securing

gages, etc.

I 5 The formulas for determining such increments are listed on p. 128.
SPECIAL THREAD DIMENSIONS AND TOLERANCES 81

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 35.

(6) 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}i

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 exactly }{, or inches for 12 threads per inch and finer, or 1, or 3, inches 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 36: Pitch diameter tolerance = 0. 0095

Also from table 35, 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 length

of engagement:

From table 37: Pitch diameter tolerance = 0. 0066

In this instance the pitch diameter tolerance is printed in italics. In accordance with the footnote under table 35 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
82 NATIONAL SCREW THREAD COMMISSION

fit may be chosen. Assuming the choice of class 3-medium fit, the

following dimensions are obtained:

From table 38: Pitch diameter tolerance = 0. 0065

From table 35 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. 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+ . 0065 =2. 9794

If, instead, it is decided to reduce the length of engagement to one-half inch, the following dimensions are obtained:

From table 37: Pitch diameter tolerance = 0. 0060

From table 35 for the screw: Maximum major diameter = 3. 0000

Minimum major diameter = 3. 0000-0. 0066 = 2. 9934

Maximum minor diameter =3. 0000-0. 0511 = 2. 9489

Maximum pitch diameter =3. 0000-0. 0271 = 2. 9729

Minimum pitch diameter = 2. 9729-0. 0060 = 2. 9669

And for the nut: Minimum major diameter = 3. 0000

Minimum minor diameter =3. 0000-0. 0451 = 2. 9549

Maximum minor diameter =2. 9549 +0. 0045 = 2. 9594

Minimum pitch diameter =3. 0000-0. 0271 = 2. 9729

Maximum pitch diameter = 2. 9729 + 0. 0060 = 2. 9789

5. GAGES

The classification of gages and gage tolerances, as well as the

thread form of plug and ring thread gages presented in section III,

division 5, " Gages" apply also to gages for special threads. In

ordering gages for a special thread, the length of engagement of the

component thread (as distinct from the length of the gage), and

the diameter, pitch, and class of fit, should be stated.

With regard to the 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 3, " Symbols." For

example, a 1-inch, 16-pitch gage of American National form of

thread, class 3, medium fit, shall be marked: 1"—18NS—3.
SPECIAL THREAD DIMENSIONS AND TOLERANCES

•> CO O © —

O £ CO a >

©

5 03 O S3"

1*1

Pi

P..9

COCS »CO

So®

S P.S2

a 3

'2 3

a a II

II

:SSS: OOOO OOOO OOOO

OOOO OOOO OOOO

HtOlCN O CO W rH to rHCO- hcocooo onsci coot

^ !5 ^ 1-1 ^ I=! CM CM CM CO CO Tfl

-g O O O O O OOOO 00(

->*< O lO H< OMNO CSlOOO CO CO lOtONO) OCOOON OOOO OOOO hhhN OOOO OOOO OOOO

tDOJINNO CO CO 10 Ttl CO CO 10 OOOO

CO CM CO CO CO I^O CO iO O O 1 OS OM00N ,00 rHrHrHCM

f-i -<-a CD o © a S| I

a I «

.2 3 M

§2©V x"-1 ©CO

o3 co fl , a ca co h a «-co © „ °a»s

a

2 a

a => la

T-H CM CN CO CO CO I :ooooo ooo< Q CM

I lO t-- CO 10 00C5H

rH CM <M CO CO •cooooo OOOOlO CO (ON(

J£ O O O O O CJa OOOO OOOO OOrH,

HCBONO CO CM • O H CO CO CO g o o o o o

.86 " '

'

I lO rH O rH

rfS o o o © o CJso

-#**!*© f- 10 10 "^OC^ NN»tO (M CM CM CO CO Tt< 10 OOOO OOOO

CO -rj< Ttno

CO _

rft CM O Cq CMO00CM CO CM CM O IOCBCBN 00OSOJ-H CM lO O CO OOOO ©OOrH rH rH CM CM OOOO OOOO OOOO

CM CO CM 00 CM O rH CM -ti 10 CONOO 1 rH tH rH rH rH CM CM -*J< © OOOO OOOO

§3;

OOOO OOOO OOOO

OOOrHrHrH rH CM CO lO

rH rH rH rH rH CM CM 00 TCH -rj< -r*< CM CO CO OOOO OOOO

> 00 O CO (M <

I rH rH rH rH 00 CO •
NATIONAL SCREW THREAD COMMISSION

Pitch

diameter

tolerances

for

diameters

up

to

and

including—

4 5

CO

'1

=!

=1

-!

-I i in : © • • -!

i !

i ii ii in

-I ! ! \ \ 11 11 1! II III

-i j 1! 11 11 Ii 11 11 HI

4 A I! II 1! 11 II II II III

-I *t It II II II II II II III

*i 4% I! II II II II II II III

4 & 11 i| ii i| i| ii i| in

~i I ii I! ii Ii Ii Ii ii ii iii

4§ 11 11 II II II II II III

4l 11 11 II II II II II III

4 In. 0.

0026 (

.0028 .0054 .0031 .0056 1.

0034

.0057 .0038 .0057 .0038 .0057 «§ 1!I II 1!

1 ii ii i

Lengths

of

engagement

S ^ ^ ^ ^

i

8 s

i i i i i 9 9 s S3 s * i
SPECIAL THREAD DIMENSIONS AND TOLERANCES 85

III 111 111 111 111

! ! 111 11! Ill III III

111 111 111 III III ill

III 111 11! Ill 111 111

IIIllI iSi lit ill ill HI

in Him in III 111 111 III

in iiini in in in in in

Q •

• UU LU L^J !_J !_!_L 111 111111 111 11! Ill III III

in mill in in in in in

in linn in in in in in

ill llllll 111 in in in in

in Him in in in in in

HI llllll 111 111 in in HI

in iiini in in in in

in iiini in in in

in iiini in

in in

: ; ; : ; : :

it it

! r

i J J J ,J 00 CD

I

I 5

IS

4

1

J

I
86 NATIONAL SCREW THREAD COMMISSION

Pitch

diameter

tolerances

for

diameters

up

to

and

including—

-I

4

4

4

4

4 111

• • 4 LI

! ! Ill III

•I S 111 111 III

1 6 inches ! 11 111 III 111

i m 1 -j—

j- 11 11 11 in in in

f II 11 I! 11 III 111 HI «=> -I

i i

i ! II H 11 II I! 11 HI HI Hi

4 11 11 11 m 11 11 11 11 111 111 111

a it ii ii ii ii ii ii ii hi in hi

»| a it ii ii ii ii .0041 .0041

.

0041

.0041

.

0041

.0041 .0041 .0082 .0045 •

.0045 .0087 .0049

.0049

'<

.0089 &| a ii ii ii ii ii li 11 is in in 111

J II 11 11 II II II 11 11 ill HI HI

In.

).0027 (

.0027 .0027 .0041 .0027 .0041 .0027 .0041 .0027 .0041 1

.0031 .0041

.0033

••

.0041 .0036 .0041 .0039 .0041 .0079

.0040

"

.0045 .0080 4g II 11 IS IS II 11 11 11 i 4l II IS IS IS IS

4l 11 11 IS i! ! i

Lengths

of

engagement

.» SSR as as SSK ; ass ass

i

* :: k ;; !«
ECIAL THREAD DIMENSIONS AND TOLERANCES 87

11! Ill 111

III 111 III 111

111 111 II! Ill

11! Ill 111 III 111

111 111

Q •

• L-L-L 111 III III

§33 Sliti SSS oSS 111 111 Hi

111 111 III 11! Ill

11! Ill HI HI HI

111 III III 111 III

III 111 III III 111

HI HI HI 111 I!

III 111 HI 111 II!

Ill III 111 HI III

111 111 III III III

ill II! Ill

III III III

TT

III

ii

i i i

<N O 00 <D

Si

If

ii

ii

it

.j

i

si

li

ii

II

II

1!

H
NATIONAL SCREW THREAD COMMISSION

Pitch

diameter

tolerances

for

diameters

up

to

and

including—

4

1 I 4

i i

j

! 4 *

: ;

! ! 4 * \

< 1

! 4

4 i 111

! '

' 4 *

0.

0080

0082'.0082 .0081 .0090 4 III ill II!

© 4 i i i :

! II I! II! Ill III

4

i i

1

! i S

i ii ii || || in in in

4 «

i it it ii ii ii H in in in

4 4gg it ii ii ii ii ii ii in in in

4 4§g I| || || I| I| || 1| HI HI HI

-I 4ii ii ii ii ii ii ii ii iii in in

xf ,11 II 11 II 11 11 11 II III III III

x| *gg H |I |I 11 11 11 1| HI HI HI

*i 4§g II 11 11 11 II II II HI III III

411 II II II II II 11 11 111 111 III

<il II II II 11 11 11 11 III i *s 4li II 11 11 11 11 i © - :

In. 0.

0014 0030

.0015 .0030 .0016 .0030 .0017 .0030

Lengths

of

engagement gl-ll-(i-lT-l

^ ^XX XX X^ XX XX XX XX XX T-(l-ll-lrH HM 1-1 CO HM

1 ao :x : 4! j ! * ; hi
SPECIAL THREAD DIMENSIONS AND TOLERANCES 89

11 III 111 III

I!! Ill 111 111 III

111 111 III 111 111

HI III III III 111 III

III 111 111 III III III

III III III III III III

111 111 III III III 111

III III III III III 111

111 II! Ill III 111 III

III III III III III 111

III III III III III 111

III III III 111 III 111

III HI HI III III 111

III III 111 III III III

HI III III III 111

Hi Hi III 111

HI III

i i

: : ! :

182129—33 7

I

II

!

If

?!

1

« S

II

1 3
90 NATIONAL SCREW THREAD COMMISSION

1

1

4 In. 0.

0056

.0062 .0062 .0057 .0064 .0066 .0057 .0065 .0072 .0057 .0065 .0077 .0058 .0065 .0078 .0058 .0066 .0078 .0059 .0066 .0079 .0066 .0079 .0102 .0066 .0079 .0103 .0066 .0079 .0104

.

0066

.0082 .0106 4 JIIIIlllIIIIlllIlllIlllIllIIIIIlI

1

^iHIIIIiiliiilllililiiililiilliii

=S jllllllllllllllllllllllllllllllll

! =1 ^lillliilllillllllllllllllllllllll

up

to

and

inclu 1

jillllilliiliiliiiiiliiliiillllll

-i ^iiiiiiiiiigigillillllilgillllligl

i ^iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiigi

1

-I

^iiiiiiiiiiiiiiiiiiiiiiiiiniiiii

I1 •I ^iiiiiigiiiiiiiiigiiiiiiigiiiinii

1

i

^iiiiiiiiiiiiiiiiiiiiiiiiiiiiini

1

^iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

-I ^illliilillliiillliilllllillllllll

-4 ^llllillllllillllliiillillllgll 1

1

!

! ^lllillllillillllllilliiilig i

In.

0.0012 (.0015

.

0033 i

.

0012

.0015 .0034

.0013

i

.0015 .0034 .0015 .0015 .0034 2

.

0016

.0016 .0035 .0016 .0018 .0035 .0016 .0020 .0036

In. i

'0.

0011 i

.

0015

.

0032 i

.

0012 i

.

0015

.0033 i

2.0013 i

.

0015

.0033

'i

.

0013 i

.

0015

.0033 i

.

0014 i

.

0016

.0034 i^ •2i

! i i i

!

;

To and

includ ing— ^ _ ^ _ _ _ i CO H M H M!OH M ^.M ..H Mffl H

!>CR ixx XX : :

: ^ r r r r r r

m r r \

Threads

per

inch

od^ooo'<o-*e^'o'
AMERICAN NATIONAL HOSE COUPLING THREADS 91

SECTION VI. 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 Off 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. The limiting dimensions herein specified have met with

general approval, including adoption as " American" standards

by the American Standards Association. State-wide adoption of

the American National fire-hose coupling threads is completed or under effective headway in 36 States, and their use has been made

compulsory by State legislative acts in California, Massachusetts,

Oregon, and Texas.

With regard to the American National hose-coupling threads,

the purpose of this specification is to provide a standard which will be recognized and adopted at once by a majority of manufacturers and

consumers and toward which the minority may be brought, thus eliminating many threads now in use and the confusion and misunderstandings that now prevail.

As in other lines of work, current practice in use and manufacture

must be recognized as well as the specific advantages of certain

thread proportions for specific uses. This prevents the adoption of a single specification for each one of the nominal sizes. These standards apply to the threaded parts of hose couplings,

valves, nozzles, and all other fittings used in direct connection with

hose intended for fire protection or for domestic, industrial, and

general service in nominal sizes of ){, %, %, 1, 1%, lji, and 2 inches.

In ordering threading tools 16 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,

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

1* 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.
92 NATIONAL SCREW THREAD COMMISSION

until the limiting 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 %Xp, or 0.125 Xp.

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

J. n^ncmw * 0.649519

h = 0.649519 Xp, or h =

where

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

h = basic depth of thread

2. THREAD series

(a) American National Hose-Coupling Threads.—There are

specified in table 40 a thread series and basic dimensions for hosecoupling threads which apply to the threaded parts of hose couplings,

valves, nozzles, and all other fittings used in direct connection with

hose intended for fire protection or for domestic, industrial, and

general service in nominal sizes of ]i t %, %, 1, !}{, and 2 inches.

Table 40.American National hose-coupling threads BASIC MINIMUM COUPLING DIMENSIONS

Nominal

size of hose (in inches) Service Number of threads

per inch Pitch Depth

of thread Majordiameter

Pitch diameter Minor

diameter

Al- low- ance

1 2 3 4 5 6 7 8 9

J4, - 94,1 Garden hose ..... 11H

8

9

14

14IV/2 im

im

Inch

0. 08696

. 12500

.11111

. 07143

. 07143

. 08696

. 08696

. 08696

. 08696

Inch

0. 05648

.08119

. 07217

. 04639

. 04639

. 05648

. 05648

. 05648

. 05648

Inches

1. 0725

1. 3870

2. 0020

.8323

1.0428

1. 3051 1.6499 1.8888

2. 3628

Inches

1. 0160

1. 3058

1. 9298

.7859

.9964

1. 2486

1. 5934

1. 8323

2. 3063

Inches

0. 9595 Inch Chemical engine and booster hose . 1. 2246

1. 8577 .7395 m Fire-protection hose ... H

Steam, air, water, and all other hose

connections. H .9500

1 1. 1921 1U 1. 5369

1. 7758

2. 2498

13/2- 2 BASIC MAXIMUM NIPPLE DIMENSIONS

H, 5A, SA—

¥i,l Garden hose. . .. . ... 11 1/ 2 8

9

f 14

14ny2 im

0. 08696

. 12500 .11111

. 07143

. 07143

. 08696

. 08696

. 08696

. 08696

0. 05648

. 08119

. 07217

. 04639

. 04639

. 05648

. 05648

. 05648

. 05648

1. 0625

1. 3750

1. 9900 .8248

1. 0353

1. 2951

1. 6399

1. 8788

2. 3528

1. 0060

1. 2938

1. 9178

.7784

.9889

1. 2386

1. 5834

1. 8223

2. 2963

0. 9495

1. 2126

1. 8457 .7320

.9425

1. 1821

1. 5269

1. 7658

2. 2398

0. 0100

.0120

.0120

.0075

.0075 .0100

.0100 .0100

.0100

Chemical-engine and booster hose... m Fire-protection hose H

Steam, air, water, and all other hose %l134 connections. IH- -

2
AMERICAN NATIONAL HOSE COUPLING THREADS 93
94 NATIONAL SCREW THREAD COMMISSION

(b) American National Fire-Hose Coupling Threads.—There

are specified in table 41 a thread series and basic dimensions for fire- hose couplings from 2}i 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% and 4y2 inches in diameter.

Table 41.

American National fire-hose coupling threads BASIC MINIMUM COUPLING DIMENSIONS

Nominal size of hose (in inches) Numberof threads

per inch Pitch Depth of thread Major

diameter

Pitch diameter Minor

diameter Allowance

1 2 3 4 5 6 7 8

2V2 m6

64

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

Inch

3zy> 4. 0473

5. 4611 BASIC MAXIMUM NIPPLE DIMENSIONS

2V2 0. 13333 0. 08660 3. 0686 2. 9820 2. 8954 0. 0150

3 6 . 16667 . 10825 3. 6239 3. 5156 3. 4073 .0150 3M 6 . 16667 . 10825 4. 2439 4. 1356 4. 0273 .0200

4 . 25000 . 16238 5. 7609 5. 5985 5. 4361 .0250

3. ALLOWANCES AND TOLERANCES

{a) Specified allowances and tolerances, given in table 42, 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 42.)

(J) The tolerance on the major diameter is twice the tolerance on the pitch diameter.

(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 (}uXp) at the root when

the pitch diameter of the nipple is at its minimum value. The maxi-
AMERICAN NATIONAL HOSE COUPLING THREADS 95

mum minor diameter is basic, but may be such as results from the

use of a worn or rounded threading tool.

(h) 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 (}iXp) when the pitch diameter of the coupling

COUPLING FORM

—A/OTA

p = Pitch

h =? B* sic7~h readDepth

f Bet sic Depth of

7>Kncat/on — 5 =• 0/08 2 S3p

H£.avy L/kiel Shows

Figure 20. American National hose-coupling and American National fire-hose coupling threads.

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(^Xp).

{%) The tolerance on the minor diameter of the coupling is twice

the tolerance on pitch diameter of the coupling. The minimum

minor diameter of a coupling is such as to result in a basic flat (Ys^p)

at the crest when the pitch diameter of the coupling is at its minimum

value.
96 NATIONAL SCREW THREAD COMMISSION

Table 42.

Tolerances and allowances for American National hose coupling and

American National fire-hose coupling threads

Nominal size of hose

(in inches) Service Threads

per inch Allowances

Toler- ances on

pitch di- ameter 1

Lead

errors consuming one

half of pitch-di- ameter

toler- ances 2

Errors in half angle consuming one

half of pitch-di- ameter

toler- ances

1 2 3 4 5 6 7

H, 5A, Yi Garden hose

8

9

14

14im

im

i t

Inch

0. 0100 .0120

.0120

.0075

. 0075 .0100

.0100

.0100

.0100 .0150

.0150

.0200

.0250

Inch

0. 0085 .0111

.0111 .0070

. 0070

.0085

.0085

.0085

.0085

.0160

.0180

.0180

.0250

Inch

0. 0025 .0032 .0032

.0020

. 0020

.0025

.0025

.0025 .0025

.0046

.0052

.0052 .0072

Deq. Min.

1 52

1 42

1 54

1 52

1 52

1 52

1 52

1 52

1 52

2 17

2 4

2 4

1 55

%, 1 1H —- -

Chemical engine and booster

hose. Fire protection hose H

H

IIK- - m —

.

22H- - 3.

Steam, air, water, and all other hose connections.

| Fire hose 3H —- m

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

full tolerance cannot, therefore, be used on pitch diameter unless the lead and angle of the thread are perfect. Columns 6 and 7 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 5. 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.

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

4. TABLES OF LIMITING DIMENSIONS

Table 43.

Limiting dimensions and tolerances, American National hose coupling

threads COUPLING THREAD

Nominal size of hose

(in inches)

Service

1

1

Threads

per

inch 1

Pitch Depth

of

thread Major diameter Pitch diameter Minor diameter

Maximum Tolerance Minimum Maximum Tolerance Minimum Maximum Tolerance Minimum

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Inch Inch In. In. In. In. In. In. In. In. In. n, %, % Garden hose... UK 0. 08696 0. 05648 i 1. 0725 1. 0245 0. 0085 1. 0160 0. 9765 0. 0170 0. 9595 %, i—

.

Chemical en- 8 . 12500 . 08119 i 1. 3870 1.3169 .0111 1. 3058 1.2468 .0222 1. 2246 g i n e and

booster hose. m— Fire protection

hose.

9 .11111 . 07217 i 2. 0020 1. 9409 .0111 1. 9298 1. 8799 .0222 1. 8577 H fl4 . 07143 . 04639 ». 8323 .7929 .0070 .7859 .7535 .0140 .7395 % Steam, air, wa- 14 . 07143 . 04639 i 1. 0428 1. 0034 .0070 .9964 .9640 .0140 .9500

i ter and all iiK . 08696 . 05648 i 1. 3051 1. 2571 .0085 1. 2486 1. 2091 .0170 1. 1921 1H other hose 11

K

. 08696 . 05648 i 1. 6499 1. 6019 .0085 1. 5934 1. 5539 .0170 1. 5369

ltt connections. 11 Vi . 08696 . 05648 i 1. 8888 1. 8408 .0085 1. 8323 1. 7928 .0170 1. 7758

2 [uy2 . 08696 . 05648 > 2. 3628 2. 3148 .0085 2. 3063 2. 2668 .0170 2. 2498

i Dimensions for the minimum major diameter of the coupling correspond to the basic flat (HXp),

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 K4XP, and may be determined by adding l%Xh (or 0.7939p) to the maxi- mum pitch diameter of the coupling.
AMERICAN NATIONAL HOSE COUPLING THREADS

Table 43.

Limiting dimensions and tolerances, American National hose coupling

threads—Continued NIPPLE THREAD

Nominal size

of hose

(in inches)

3A, 1- 1HH-%-

1_. mm2_.

Service

Garden hose Chemical en- gine and

booster hose. Eire protection

hose. Steam, air, water and all other hose

connections.

14

1411*2 im

Inch

0. 08696

12500

, 11111

. 07143

, 07143

, 08696

Inch

0. 05648

.08119

.07217

, 04639

. 04639

, 05648

, 05648

05648 05648

Major diameter

In

1. 0625

1. 3750

1.9900 .8248

1. 0353

1. 2951

1. 6399

1. 8788

2. 3528

In

0. 0170 0222

.0222

.0140 0140

0170

0170

0170

0170

In

1. 0455

1. 3528

1. 9678

.8108

1. 0213

1. 2781

1.6229

1. 8618

2. 3358

Pitch diameter

1.9178 .7784

.9889

1. 2386

1.5834

1. 8223

2. 2963

In.

0. 0085

.0111

.0111 .0070

.0070

,0085

,0085 0085

,0085

11

In

0. 9975

1. 2827

1. 9067

.7714

.9819

1. 2301

1. 5749

1. 8138

2. 2878

Minor diameter

In

2 0. 9495

2 1. 2126

2 1. 8457

2. 7320

2. 9425

2 1. 1821

2 1. 5269

2 1. 7658

2 2. 2398

In. In.

1 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 H4XP, and may be determined by subtracting l%Xh (or 0.7939p) from the minimum pitch diameter of the nipple. Table 44.

Lengths of threads for American National hose-coupling threads L

Nominal

size of hose (in inches)

%, 1—

m.—H

%

11Hm2.

Threads Length Depth

Service per

inch,

of nipple, of coupling, n L H

Inch Inch Garden hose WVi Me i7A2

Chemical engine and boost- 8

er hose. Fire protection hose 9 H

f 14 H

15/32 14 Me

Steam, air, water, and all other hose connections.

ll 1/! Me 17A2

11 H % 1SA2

5A i%2

{ nn n 2%2

Thread

length

for coupling, T

Inch

*%2 Me

15/32 15A2

19A2

Length

of pilot, /

Inch

Inside diameter of nipple, C

Inches 2%2 1%

*%2 1H2

1%2

11^2 2^2

Approximate number

of threads

in length T

4H

4Mm
98 NATIONAL SCREW THREAD COMMISSION

Table 45.

Limiting dimensions and tolerances, American National fire-hose coupling threads COUPLING THREAD

Nominal

size of hose

(in inches) Threads

per inch Pitch Depth

nfOI thread

Major diameter Pitch diameter Minor diameter

Maxi- mumToler- ance Mini- mum

Maxi- mum

Toler- ance Mini- mumMaxi- mumToler- ance Mini- mum

1 2 3 4 5 6 7 8 9 10 11 12 13

2y2 6

64

Inch

0. 13333

. 16667

. 16667

. 25000

Inch

0. 08660

. 10825+

. 10825+

. 16238

Inches Inch Inches

1 3. 0836

1 3. 6389

14. 2639

1 5. 7859

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

33M

iH NIPPLE THREAD

2y2 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

2 2.8954

3 2 3. 4073 33^ - 24. 0273 m 5. 5735 2 5. 4361

1 Dimensions for the minimum major diameter of the coupling correspond to the basic flat (HXp),

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 H*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 nippl

shall be that corresponding to a flat at the minor diameter of the minimum nipple equal to and may be determined by subtracting l%Xh (or 0.7939p) from the minimum pitch diameter of the nipplee

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 46. Limiting dimensions for

these gages are given in tables 47 and 48.

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 47 and

48, 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 46.

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

1 2 3 4

Inch ±0. 0005 Deg. Min. ±0 10 Inch

/ -0. 000

\ +. 001

Inch +0. 000 -.001
AMERICAN NATIONAL PIPE THREADS 99

Table 47.Limiting dimensions of field inspection thread plug gages for couplings

{internal threads) 1

Nominal

size of hose Threads

per inch

"Go" or minimum gage "Not go" or maximum gage

Major diameter Pitch diameter Major diameter Pitch diameter

Maxi- mum

; Mini- mum

Maxi- mumMini- mumMaxi- mumMini- mumMaxi- mumMini- mum

1 2 3 4 5 6 7 8 9 10

2.500 3.000

3.500 4.500

6

64

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 a 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 48.

Limiting dimensions of field inspection thread ring gages for coupling

nipples {external threads) 1

Nominal

size of hose Threads

per inch

"Go" or maximum gage "Not go" or minimum gage

Pitch diameter Minor diameter Pitch diameter Minor diameter

Maxi- mumMini- mumMaxi- mumMini- mumMaxi- mumMini- mumMaxi- mumMini- mum

2 3 4 5 6 7 8 9 10

2.500

3.000

3.500

4.500 m664

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. 04S3

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 VII. AMERICAN NATIONAL PIPE THREADS

The material on the subject of pipe threads 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 en- 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. The material on gages for pipe threads

has, however, been extensively revised.
100 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. 17—The crest and root of the thread form are truncated an amount equal to 0.0330^; the depth of thread is, therefore, equal to O.Sp.

Figure 21.American National taper pipe thread form and notation. NOTATION

^.=60° angle of thread

a =30° one half angle of thread

y = l° 47' approx. taper angle=one sixteenth inch per inch on diameter

IJ=0.866025p depth of 60° sharp V thread "

h{=0 923761?Jdepth of thread on work

(=0:033012pl

f\ =0.038120mdepth of truncation

l=0.041266ft ) p=l/n pitch (measured parallel to axis) 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.

While Mr. Briggs originally advocated a slightly rounded crest and root, cutting tools are actually

slightly flattened at the crest and root.

18 p p

For a symmetrical straight screw thread, cot a - For a symmetrical taper screw thread H=

(cot a—tan2 y tan a), so that the exact value for an American National taper pipe thread is i?=0.865743p

as against H=0.S68025p, the value given above. For an 8-pitch thread, which is the coarsest standard taper pipe thread pitch, the corresponding values of i7are 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 H=0.866Q25p continues in use for threads of three fourths inch, or less, taper per foot.
AMERICAN NATIONAL PIPE THREADS 101

2. SYMBOLS

The list of symbols given in section II, 3, 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 Ejl

Pitch diameter of thread at L2 from end of pipe Er. 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__

Length of effective thread L2 Outside diameter of pipe =major diameter of pipe thread at L2 from end of pipe D

Internal diameter of pipe d Lz = LenjfA ofeffect/re f/rreac?- m/ber/ectthreads, dlue A> Aacifct/e^

o/J>Jjbe = D

Eg^F/tcA d/atr?. of Zenith Z_2

£/~Pitch J/an. offArectc? ofJb/fe

Figure 22.

American National taper pipe thread notation. NOTATION

Eo = D-(O.Q5D+l.l)p

.Ei = £b+0.0625ii

Z-2 =p (0.8.D+6.8) fc=0.8p

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 49.

1. Outside diameter of pipe.—The outside diameters of pipe are given in column 5 of table 49.

2. Diameters of taper threads.—The pitch diameters of the taper

threads are determined by formulas based on the outside diameter
NATIONAL SCREW THREAD COMMISSION

ill!* 2 Inches 0.

33388

.

43294

.

56757

.

70129

.

91054 1.

14407 1.

48757 1.72652 2.

19946 2.

61953 3.24063 3.73750 4.

23438 4.

73125 5.

29073 6.

34609 7.33984 8.33359 9.32734

10.

44531

1

1

iiii• • • • III H H H d N lllll

COW^uS

Hi

d^odd©

tn

S3 iff I

iiii III ill! IIIII

^d " ' * " hhhnn oieorfi^ui decode

a

.2

13

-do I

<

a

1 S iiiii • mi iiiii mil • • • rH^rHC4<N CO d T*i ^ d «5 ^ CO OS ©

At

end

of

pipe,

or

at

length

L\

from

end

of

coupling, n i

PQ

«*> Inches

0.

36351

.

47739

.

61201

.

75843

.

96768 1.21363 1.55713 1.79609 2.26902 2.71953 3.34062 3.

83750 4.33438 4.

83125 5.

39073 6.44609 7.43984 8.43359 9.42734

10.

54531

Increase in diameter per

thread,

0.0625 n 00 iiini iiiii iiiii mil

t>- pini mi nil nil

of

normal

engage- ment

by

hand, Li ce iiini iiiii sails §§§§§

Outside diameter of

pipe, D i« jlilii §§§gg iilil lllll |d -

* "rn ^J^tfe* cc^dd dNOOOiO

Depth

of

thread, h «* iiini mil mil inn

b

ffO -iiiii IIII lllll Ml

Number of threads per

inch, oooooooo

I

.9•11

I

a1

iiiii Jiiji Ml jJJjj
AMERICAN NATIONAL PIPE THREADS

mis urn m

fill fill ill

lill illll III

urn urn in

mil mil in

mil mi in (M

- NMNtq ei Ci <N CO CO CO CO CO

^- §§§lg 111

-i <N oi pi <N Csi (M

- Kslll

32:532

illll 111

assess sss ooooo ooooo Illll li!

i222 22222

i co oo oo oo oo <

; ;000 OOOOO OOO
104 NATIONAL SCREW THREAD COMMISSION

of pipe and the pitch of thread. These are as follows 19 (see Symbols

above):

E = D-(0.05D+l.l)p

£'

1 = £

,o + 0.0625Z1 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 19 (see Symbols above):

L2 =(0.8D + 6.8)p

J+. 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 49. 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.20 (6) American National Straight Pipe Threads.—The specified sizes and basic dimensions on the " American National straight

pipe threads" are given in table 50.

1. Diameters of 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):

Ex = D- (0.05D + 1 . 1 )p + 0.0625^!

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. 21 (See columns 4 and 6 of table 50.)

« 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.

20 See figs. 29 and 30.

21 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 scratch and

not at the end of the coupling when the thread is chamfered.
AMERICAN NATIONAL PIPE THREADS 105

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

£) = basic bitch diameter- = pitch diameter at

length L, from end of taper threaded r'J" see table: so roR RELATION TO TAPER THREAD Figuke 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 bottom of the chamfer (first thread scratch) with the gaging notch, allowing a maximum variation of one and onehalf turns plus or minus from the notch. 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.

Table 50.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, Ei Minor

diameter 1 Maximum Basic Minimum Basic

1 2 3 4 5 6 7 Inches Inches Inches Inches Inches H ----- 27 .0. 40439 0. 37823 0. 37476 0. 37129 0. 34513 Hn~

18 . 53433 . 49510 . 48989 . 48468 .44544

18 . 67145 . 63222 . 62701 . 62181 . 58257

14 . 83557 . 78513 . 77843 . 77173 .72129 h 14 1. 04600 . 99556 .98887 . 98217 . 93172

i im 1. 30819 1. 24678 1. 23863 1. 23048 1. 16907 1H 1. 65294 1. 59153 1. 58338 1. 57523 1. 51382 m - \\Yi 1. 89190 1. 83049 1. 82234 1.81418 1. 75277

2... ____ im 2. 36583 2. 30442 2. 29627 2. 28812 2. 22671 m - 3„

8 2. 86216 2. 77388 2. 76216 2. 75044 2. 66216

8 2. 48850 3. 40022 3. 38850 3. 37678 3. 28850 m 8 3. 98881 3. 90053 3. 88881 3. 87709 3. 78881

4 8 4. 48713 4. 39884 4. 38712 4. 37541 4. 28713 m - 8 4. 98594 4. 89766 4. 88594 4. 87422 4. 78594

5... 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. 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

182129—33 8
106 NATIONAL SCREW THREAD COMMISSION

the 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

AMERICAN M4T/OZV4L AMtR/CAW A//IT/0ML

Figure 24.

Illustration of "long screw" joint between straight threaded coupling

and taper threaded pipe.

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

MAXM1VM PITCH OifiM. £XTERNAL LOCK NUT TH&SAD Figure 25.

American National locknut thread notation. NOTATION

Ei = pitch diameter at gaging notch of American National taper plug gage .Ee=-Ei+(4pX0.0625)

-Ei = .Ei+(5pX0.0625) Note—See table 51 for relation to taper pipe thread. 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.

(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

' 1 maximum external and minimum

internal locknut threads." For dimensions, see table 51. The "tank
PIPE DIMENSIONS 107

nipple " shown in figure 26 is an example of this thread. In this application an American National standard taper pipe thread is cut on the

end of the pipe after having first cut the 1 'external locknut thread."

7>7/V/r WALL. /NTEftf/AL LOCKMr

EXTEWiL.

Figure 26.Illustration of

"'tank nipple" thread. Table 51.

Dimensions of American National locknut threads

[For notation, see fig. 25]

Nominal sizes (in inches) Threads

per inch Et (maxi- mum)

(mini- mum)

H-HHH-H1.. m

2... 2H

3..

4_. m

5-

6-7„

8.. 9-

10. 11.

12.

27

18

18

14

14\m

11^

Inches

0. 38402

. 50378

. 64090

. 79629

1. 00672

1. 26037

1. 60512

1. 84408

2. 31801

2. 79341 41975 92006

41838

91719

5. 48054

6. 53722

7. 53359

8. 53128

9. 52922

10. 65219

11. 65063

12. 64906

Inches

0. 38633

. 50725 .64437

. 80075

1.01119

1. 26580

1. 61055

1. 84951

2. 32345

2. 80122

3. 42756

3. 92787

4. 42619

4. 92500

5. 48836

6. 54503

7. 54141

8. 53909

9. 53703

10. 66000

11. 65844

12. 65688

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 E, and plus on Ei.

4. TABLES OF PIPE DIMENSIONS

Tables 52, 53, 54, and 55, which follow, are not a part of the

thread standard, but are reprinted as part of the Manual on American Standard Pipe Threads.
108 NATIONAL SCREW THREAD COMMISSION

Table 52.Dimensions of standard wrought pipe

Nominal sizes (in inches)

Hm.

m.

2... 2H3... 3^.

4... m 1 5...

6... 71..

8 i._ 8...

9 i._ 10 1. 10 1. 10..

11 i. 12 1. 12..

Inside diameter

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

Outside diameter

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

Nominal

thickness

Inch

0. 068

.088

.091 .109

.113

. 133

. 140 .145 .154

.203

.216 .226

.237

.247

.258 .280

.301 .277 .322 .342

.279 .307

.365

.375

.330

.375

Transverse areas

Internal Metal

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

.333 .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

Length

of pipe

per square

foot of external

surface

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 .686

.576 .500

.442

.442

.396

.355 .355

.355

.325

Nominal

weight

per foot threaded and

coupled

Pounds

0.245 .425

.568

.852

1. 134 1.684

2.281

2. 731

3. 678

5. 819

7. 616 9.202

10. 889

12. 642

14. 810

19. 185

23. 769

25. 000

28. 809

34. 188

32. 000

35. 000

41. 132

46. 247

45. 000

50. 706

i Not included in simplified list of sizes as given in Department of Commerce Simplified Practice Recommendation R57-32. Table 53.

Dimensions of extra strong 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

Nominal

weight

per foot, plain ends

HH.%.

Yi- U.

1_. 1H

2.. 3..

4.. 5._

6_. 71.

8..

9 1. 10. 11

1

12.

Inches

0. 215 .302

.423

.546 .742

.957

1.278

1. 500

1. 939

2. 323

2. 900

3. 364

3. 826 4.290

4.813

5. 761

6. 625

7. 625

8. 625

9. 750

10. 750

11. 750

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

9. 625

10. 750

11. 750

12. 750

Inch

0.0£ .119

,126

.147 ,154

,179

,191 ,200

,218 ,276

,300

,318 ,337

,355

.375

,432

,500 ,500

,500

,500

,500 .500

Square

inches

0. 036 .072

.141

.234

.433

.719

1. 283 1.767

2. 953 4.238

6. 605

8. 888

11. 497

14. 455

18. 194

26. 067

34. 472

45. 663

58. 426

74. 662

90. 763

108. 434

Square

inches

0. 093 .157 .217

.320

.433

.639

.881

1. 068

1. 477

2. 254

3. 016

3. 678

4. 407

5. 180 6.112

8. 405

11. 192

12. 763

14. 334

16. 101

17. 671

19. 242

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

.686 .576

.500 .442

.396

.355

.325

.299

Pounds

0. 314 .535

.738

1. 087

1. 473

2. 171

2. 996

3. 631

5. 022

7.661

10. 252

12. 505

14. 983

17. 611

20. 787

28. 573

38. 048

43. 388

48. 728

54. 735

60. 075

65. 415

i Not included in simplified list of sizes as given in Department of Commerce Simplified Practice Recommendation R57-32.
GAGES FOR PIPE THREADS

Table 54.Dimensions of double extra strong wrought pipe

109

Nominal sizes (in inches) Inside diameter

Outside

diameter Nominalthickness

Transverse areas

Internal Metal

Length

of pipe

per square

foot of external

surface

Nominal

weight

per foot, plain ends

H-U1.. w

m

2__ 2%

3 i. 3%

4__ 4%

5.. 6.. 7/

Inches

0. 252 .434

.599

.896

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

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

Inch

0. 294 .308

.358

.382

.400

.436 .552

.674 710

750

875

875

Square

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

328

091 954

848

763 686

576 500 442

Pounds

1. 714

2. 440

3. 659

5. 214

9. 029

13. 695

18. 583

22. 850

27. 541

32. 530

38. 552

53. 160

63. 079

72. 424

1 Not included in simplified list of sizes as given in Department of Commerce Simplified Practice Recommendation R57-32. Table 55.

Diameters of large O.D. pipe

Nominal sizes (in inches)

Outside diameter

Inside diameter % inch

thick %6 inchthick % inchthick %6 inchthick % inchthick inch

thick % inchthick % inch

thick

1 inch

thick

1 2 3 4 5 6 7 8 9 10 11

14 Inches

14

15

1617

1820

2224

26

2830

Inches im

14% 15%

16%

17/2

Inches 13%

14%

15%

16%

17%

19%

213/8

Inches

13 H im

151/4 1634 17H

19J4 21%

23 %

2514

Inches 13%

14% 15%

16%

17%

19% 21%

23% 25%

27% 29%

Inches

13

14

1516

17

19

2123

25

2729

Inches 12%

13%

14% 15%

16%

18% 20%

22%

24%

27% 28%

Inches 12% 13%

14?4 15%

16%

18% 20%

22%

24%

26% 28%

Inches 12%

13% 14%

15% 16%

18% 20%

Inches

12

13

14

1516

18

15

16

17

182022

24 22%

26 24/2

28 26%

30 28%

5. GAGES

(a) FUNDAMENTALS

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.

(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 design of gages required for the various inspection operations.

Basic dimensions of taper pipe thread gages are given in table 57
110 NATIONAL SCREW THREAD COMMISSION

All such gages should be made to the basic dimensions within the

tolerances for each element given in table 56 and footnotes thereto.

It is possible for taper thread plug and ring gages, which come within

the tolerances specified for each element, to vary from being flush

with each other at the gaging end, or at the gaging notch, when

screwed together tightly by hand. The maximum variation which

might occur and be permissible, expressed in terms of longitudinal

distance or stand-off, is given in column 9 of table 56. In order properly to maintain interchangeability of pipe threads,

gages should consist of "master," "checking," "inspection," and

"working" gages.

1. Classification of Gages—(a) Master gage. —The master gage

is a taper threaded plug gage. (See fig. 27.) It is the gage to which

all other gages are ultimately referred, either by transfer of measurers PER /IN 16. MEASURED ON

DIAMETER

ROOTS ARE UNDERCUT

TO FACILITATE GRINDING

CAGING NOTCH

fh"0-' -J

1

Figure 27.Master gage or check gage for checking inspection gages. ments or direct comparison by engagement. It is intended primarily

for the use of gage and thread tool manufacturers. It should be made

to the basic size as accurately as possible and be within the tolerances

given in table 56. Each master gage shall be marked with an identification number

or symbol, and be accompanied by a report showing the error on each

of the elements of thread and a statement of the accumulative error derived from the errors in the various elements. In case of question,

the deviations of this gage from the basic size shall be ascertained by

the Bureau of Standards at Washington, D.C.

(b) Checking plug gage.-—The checking plug gage is similar in all respects to the master gage, and is used to inspect inspection and

working taper threaded ring gages.

(c) Inspection gages.-—Inspection gages consist of one taper threaded

plug gage and one taper threaded ring gage.

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
GAGES FOR PIPE THREADS 111

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 frequently

and in use their errors should be taken into account.

(d) 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

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.

2. Thread Form of Taper Pipe Thread Plug and Ring

Gages.—The roots of the threads of all taper pipe thread gages are

Figure 28.

Inspection or working gages for checking product.

cut to sharp V or may be undercut to facilitate making the thread.

The crests are truncated an amount equal to O.lp, but otherwise the

gages are made to the dimensions given in table 49.22

(c) GAGING PRACTICES

A common practice in the gaging of taper pipe threads is illustrated

in figures 27, 28, 29, and 30. However, other practices, some of which

may be equally satisfactory, are widely used.

The basic gaging length is equal to the dimension Lx

. In figures 27

and 28 this dimension is shown as the thickness of the ring gage, and

as the distance from the small end to the gaging notch of the plug gage.

1. Gaging Internal Threads.—The inspection and working

plug gages, figure 29, should screw tight by hand 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,

(first thread scratch). The fitting or coupling is within the working

or net tolerance if the working gage notca is within one turn of the

m The object of truncating the crests on gages (truncation O.lp) 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.
112 NATIONAL SCREW THREAD COMMISSION

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 face when screwed on tight by hand.

AMERICAN NATIONAL TAPE/?

iNTERMflL THREAD INTERNAL. THREAD /NTERNAL. THREfiQ

BASIC S/Z£ MfiX/"7t/M S/Z£ MlNtntU/ri SIZE

Figure 29.Gaging of internal American National taper pipe threads. This method of gaging is used either for taper internal threads or

for straight internally threaded couplings which screw together with

taper external threads.

2. Gaging Taper External Threads.—The ring gage, figure 30,

should screw tight by hand on the pipe or external thread until the

AMERICAN fi/ATIOH/\L TAPE/? INSPECTION fi>if*G GAGE ONE AND ONE-NALR TURNS LAr?Cr£ ONE AND ONE-HALF

TURNS S/W-t-

£XTERNAL THREAD

BASfC SIZE EXTERNAL THREAD MAXIMUM STT.E EXTERNAL THREAD

MtN/OnuM SIZE. Figure 30.

Gaging of external American National taper pipe threads. 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.
GAGES FOR PIPE THREADS 113

Table 56.

Tolerances for American National taper pipe thread plug and ring

gages

Nominal sizes

(in inches) Number

of threads

per inch

Toler- ance on

pitch diameter 1

(includ- ing

taper)

Toler- ance on

Toler- ance on

half angle of thread

Toler- ance on

major

diameter

of plug

Toler- ance on minor

diameter

of ring

Maxi- mum

longitu- dinal variation from

basic for plug or ring gage

Maxi- mum

stand-off between

plug and

ring gages at gaging end when

screwed

together

tightly by hand

H

H3A

H

H

lIX—

1*4—

22*4—

3.3*4—

4.4*4—

56

8

1012

14 O.D

16 O.D

18 O.D

20 O.D

24 O.D

27

1818

141411*4

11*4

11*4 11*4

Inch

0. 0002

.0003

.0003 .0003

.0003

.0003

.0003

.0003 .0003 .0004

.0004

.0004

.0004

.0004

.0004 .0004

.0005

.0005

.0005

.0006 .0006

.0006

.0006

.0006

Inch ±

0. 0002 .0002

.0002 .0002

.0002

.0003

.0003

.0003

.0003 .0004

.0004

.0004 .0004

.0004

.0004

.0004

.0005

.0005 .0005

.0006

.0006

.0006

.0006

.0006

Deg. Min

±

10

1010

8

Inch +

0.0005

.0005 .0005

.0010 .0010

.0010

.0010

.0010

.0010

.0015 .0015

.0015

.0015

.0015

.0015

.0015 .0020

.0020 .0020

.0025

.0025

.0025

.0025 .0025

Inch

0. 0005 .0005

.0005 .0010

.0010

.0010

.0010 .0010

.0010

.0015 .0015

.0015

.0015

.0015

.0015

.0015 .0020 .0020

.0020

.0025 .0025

.0025

.0025

.0025

Inch

0. 0115 .0144

.0144

.0146

.0146

.0181

.0181

.0181

.0181 .0219

.0219

.0219 .0219 .0219

.0219

.0219 .0264

.0264

.0264

.0307

.0307

.0307

.0307 .0307

Inch

0. 0230

.0292

,0292 0362

,0362 ,0362

,0362

,0438

,0438

,0438

,0438

,0438

,0438

,0528

,0528 0528

0614

,0614 0614

0614

0614

1 The taper of the pitch diameter cone shall be such that the pitch diameter will be within the tolerance given at all points. For example, if the gage is to maximum size at the small end, the taper shall not be

greater than 0.750 inch taper per foot. If a gage is to minimum size at the small end, the taper shall not be

less than 0.750 inch taper per foot.

2 Pitch diameter tolerance is to be applied plus on plug gages (other than checking plug gages) ; minus on

checking plug gages and ring gages.

3 Allowable variation in lead between any 2 threads. Note.—The tolerance for the height from the gaging end to notch of all plug gages shall be plus 0.000 inch, minus 0.001 inch for sizes *6 inch to 2 inches, inclusive, and plus 0.000 inch, minus 0.002 inch for sizes 2*4 to 24 inches, inclusive. The tolerance for the over-all thread length of plug gages shall be plus *32 inch, minus 0.000 inch for sizes

*£ inch to 2 inches, inclusive, and plus *l6 inch, minus 0.000 inch for sizes 2*4 to 24 inches, inclusive. The thickness of the ring gage shall be held within a tolerance of plus 0.001 inch, minus 0.000 inch for sizes *£ inch to 2 inches, inclusive, and plus 0.002 inch, minus 0.000 inch for sizes 2*4 to 24 inches, inclusive
114 NATIONAL SCREW THREAD COMMISSION

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GAGES FOR PIPE THREADS

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116 NATIONAL SCREW THREAD COMMISSION

SECTION VIII. AMERICAN NATIONAL SCREW, BOLT, AND

NUT PROPORTIONS 23 A project to which the Commission gave early attention was the

standardization of bolt and nut proportions. 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 standards for wrench-head bolts

and nuts which are referred to below.

The Commission endorses the standards for proportions of the fol- lowing threaded products as listed in the references below:

Bolt heads: Reference Heavy 2 Regular 1, 2 Cap screw heads, hexagon 2 Cap screws, slotted head 3, 4 Carriage bolts: Countersunk 5 Fin-neck 5 Ribbed 5 Square-neck 1, 5 Castellated nuts 1, 2 Heavy nuts 2 Jam nuts 1, 2 Jam nuts, heavy 2 Light nuts 1, 2 Regular nuts 1, 2 Machine bolts 1 Machine bolts, button-head 1, 5 Machine screws, slotted-head 3, 4 Machine screw nuts 2 Plow bolts 8

Set screws 2, 3 Step bolts 5 Stove bolts 3 Stove bolt nuts 2 Tap rivets 1 Track bolts 7 Track bolt nuts 7 Wood screws 4, 6

1. Federal Specification for Bolts, Nuts, Studs, and Tap Rivets (and material

for same). No. FF-B-571, October 13, 1931. Promulgated by the Federal

Specifications Board. Sold by the Superintendent of Documents, Washington, D.C. Price 10 cents.

2. American Standard Wrench-head Bolts and Nuts and Wrench Openings.

Report No. B18. 2-1932, issued and sold by the American Standards Association, 29 West Thirty-ninth Street, New York, N.Y. Price, 50 cents.

3. Federal Specification for Screws, Machine, and Set; and Bolts, Stove, No.

FF-S-91, April 22, 1933. Available at the Bureau of Standards in mimeographed form.

4. American Standard Slotted Head Proportions—Machine Screws, Cap Screws,

and Wood Screws. Report No. B18c-1930, issued and sold by the American

Standards Association, 29 West Thirty-ninth Street, New York, N.Y.

Price, 45 cents.

5. American Standard Round Unslotted Head Bolts—Carriage, Step, and

Machine Bolts. Report No. B18e-1928, issued and sold by the American

Standards Association, 29 West Thirty-ninth Street, New York, N.Y.

JPrice 40 cents

6. Federal Specifications for Screws, Wood, No. FF-S-111, April 28, 1931. Promulgated by the Federal Specifications Board. Sold by the Superintendent of Documents, Washington, D.C. Price, 5 cents.

23 See also appendix 5, p. 161.
OIL-WELL EQUIPMENT THREADS 117

7. American standard track bolts and nuts. Report No. B18d-1930, issued and

sold by the American Standards Association, 29 West Thirty-ninth Street, New York, N.Y. Price, 40 cents.

8. Plow Bolts. United States Department of Commerce Simplified Practice Recommendation R23, February 19, 1924. Issued by the Bureau of Standards and sold by the Superintendent of Documents, Washington, D.C.

Price, 5 cents. Also published as Report No. B18f-1928, 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. MISCELLANEOUS SPECIAL THREADS

Section IX A. 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 MidContinent Oil and Gas Association in 1921, but this was complicated by

a proposal to simplify casing sizes and weights, and provide 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, cer- tain 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. Standard No. 5-A, "Pipe

Specifications", issued by the division of standardization, American

Petroleum Institute, 1508 Kirby Building, Dallas, Tex.

The Commission endorses 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 tools. 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 oil-well pumps (barrels, plungers, valves, etc.). No. 11-B. A.P.I, sucker rod specifications.

Section IX B. American National Standard Hose Connections for Welding and Cutting Torches

The specifications given herein, covering hose connections for

welding and cutting torches, were 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 various manufacturers.

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 their

usual practice as much as possible. Two sizes of connections are

specified, as illustrated in figures 31 and 32.
118 NATIONAL SCREW THREAD COMMISSION

1. STANDARD DIMENSIONS

1. Screw threads corresponding to the American National fine- thread series, and class 3, medium fit, are specified in figures 31 and

32, for which dimensions are given in table 13. Right-handlfhreads

are specified for oxygen and left-hand threads for fuel gas.

2. Angle and outside diameter of internal seat.

3. Radius and distance of radius center of external seat from shank

shoulder.

4. Diameter of shank shoulder.

5. Diamter 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 31 and 32.

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 con- nection 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 33. B size hose connection, as shown in figure 38.

2. "Go" adjustable thread-ring gage for right-hand nipple thread: A size, %-24NF-3:

Minor diameter, maximum, 0.3299; minimum, 0.3294 inch. Pitch diameter, maximum, 0.3477; minimum, 0.3474 inch. B size, %6-18NF-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, 3/8-24NF-3LH:

Minor diameter, maximum, 0.3299; minimum, 0.3294 inch. Pitch diameter, maximum, 0.3477; minimum, 0.3474 inch. B size, %6-18NF-3LH:

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, %-24NF-3:

Minor diameter, maximum, 0.3304; minimum, 0.3299 inch. Pitch diameter, maximum, 0.3458; minimum, 0.3455 inch. B size, %6-18NF-3:

Minor diameter, maximum, 0.5029; minimum, 0.5024 inch. Pitch diameter, maximum, 0.5237; minimum, 0.5234 inch.
WELDING-TORCH HOSE CONNECTIONS 119

Hose A B c

Inch MeXInch %2

Yl6

Inch MeH

Inch

n 000

187+ .000

• 187 - .005

Figure 31.

"A" size of standard hose connections for welding and cutting torches.

Hose A B C

Inch %

MeU

MeH

Inch H

MeX

%2He

Inch %

Me

J4Me

Inch

4

o n+o. 000

,.,-+0. 000

.005

o 19+ .000

• 6U- .005 250+ • 000

.005 1R7+ .000

• 187 - .005 Figure 32.

" B" size of standard hose connections for welding and cutting torches.
120 NATIONAL SCEEW THREAD COMMISSION

55

Figure 33."Go" and 11 not go" gage for depth of threaded recess, and shank bore, A size.

Figure 34.Taper gage for nipple seat, A size

A.

N i% O0IS)

Figure 35.

"Go" ring gage for diameter of shank shoulder and concentricity of serrated portion, A size.

! *2

.164

/25" 5

'-lee 1 f —* jf—.040" T

Figure 36.

Master template for nose of shank, A size.

.os4 R

J2S"

<64

i— .093R

Figure 37.Template gage for nose of shank, A size. -Li

-O £ !?!? r- I Figure 38.

"Go" and "not go" gage for depth of threaded recess, and shank bore, B size.
WELDING-TORCH HOSE CONNECTIONS 121

Gage no.

5. "Not go" adjustable thread-ring gage for left-hand nipple thread

A size, H-24NF-3LH:

Minor diameter, maximum, 0.3304; minimum, 0.3299 inch. Pitch diameter, maximum, 0.3458; minimum, 0.3455 inch. B size, %6-18NF-3LH:

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, H-24NF-3:

"Go" end: Major diameter, maximum, 0.3750; minimum, 0.3740 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, %6-18NF-3:

"Go" end: Major diameter, maximum, 0.5625; minimum, 0.5620 inch. Pitch diameter, maximum, 0.5262; minimum, 0.5259 inch. "Not go" end: Major 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, %-24NF-3LH:

"Go" end: Major 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, %6-18NF-3LH:

"Go" end: Major diameter, maximum, 0.5625; minimum, 0.5620 inch. Pitch diameter, maximum, 0.5262; minimum, 0.5259 inch. "Not go" end: Major diameter, maximum, 0.5548; 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, H-24NF-3:

"Go" end: Major diameter, maximum, 0.3755; minimum, 0.3750 inch. Pitch diameter, maximum, 0.3484; minimum, 0.3481 inch. Gaging notch, 0.125 inch from back. "Not go" end: Major diameter, maximum, 0.3665; minimum, 0.3660 inch. Pitch diameter, maximum, 0.3503; minimum, 0.3500 inch. B size, Me-18NF-3:

"Go" end: Major diameter, maximum, 0.5630; minimum, 0.5625 inch. Pitch diameter, maximum, 0.5269; minimum, 0.5266 inch. Gaging notch, 0.125 inch from back. "Not go" end: Major diameter, maximum, 0.5510; minimum, 0.5505 inch. Pitch diameter, maximum, 0.5294; minimum, 0.5291 inch.

9. "Go" and "not go" double-end thread plug gage for left-hand nut thread: A size, H-24NF-3LH:

"Go" end: Major diameter, maximum, 0.3755; minimum, 0.3750 inch. Pitch diameter, maximum, 0.3784; minimum, 0.3481 inch. Gaging notch, 0.125 inch from back. "Not go" end: Major diameter, maximum, 0.3665; minimum, 0.3660 inch. Pitch diameter, maximum, 0.3503; minimum, 0.3500 inch.

182129—33 9
122 NATIONAL SCREW THREAD COMMISSION

Figure 39.

Taper gage for nipple seat, B size.

4.250* :I96R

.054-

FlGURE 41. -Master template for nose of shank, B size.

Figure 42.Template gage for nose of shank, B size.
ELECTRIC SOCKET AND LAMP BASE THREADS 123

Gage no. 9. "Go" and "not go" double-end thread plug gage for left-hand nut thread

Continued.

B size, ^6-18NF-3LH:

"Go" end: Major diameter, maximum, 0.5630; minimum, 0.5625 inch. Pitch diameter, maximum, 0.5269; minimum, 0.5266 inch. Gaging notch, 0.125 inch 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 34. B size, as shown in figure 39.

11. "Go" ring gage for diameter of shank shoulder and concentricity of serrated

portion:

A size, as shown in figure 35. B size, as shown in figure 40.

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 K-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 36. B size, as shown in figure 41.

19. Template gage for nose of shank: A size, as shown in figure 37. B size, as shown in figure 42. Section IX C. 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 shown in figure 43.
124 NATIONAL SCREW THREAD COMMISSION

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 58. SOC/f£T SCftBW SHELL.

S 5 5 $

\\w

lilt lili

till

Figure 43.

Illustration ofallowance and tolerances, American National rolled threads

for screw shells of electric sockets and lamp bases. The corresponding dimensions and limits for socket screw shells,

which are used in electric sockets, receptacles, and similar devices, are given in table 59. Table 58.

American National rolled threads for lamp base screw shells

Threads

per inch Depth of thread

Major diameter Minor diameter

Size Pitch Radius

Maxi- mumMini- mumMaxi- mumMini- mum

1 2 3 4 5 6 7 8 9

Miniature . . ... . 14 Inch

0. 07143 Inch

0. 020 Inch

0. 0210 Inches0. 375 Inches0. 370 Inches0. 335 Inches

0. 330 Candelabra 10

9

. 10000 .025 .0312 .465 .460 .415 .410 Intermediate. . . 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
ELECTRIC SOCKET AND LAMP BASE THREADS 125

Table 59.

American National rolled threads for socket screw shells

Size Threads

per inch Pitch Depth of thread Radius

Major diameter Minor diameter

Maxi- mumMini- mumMaxi- mumMini* mum

1 2 3 4 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

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 gages

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.

(6) Gaging op 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 gages 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 percent of the tolerance on the product, and should be applied in such 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 58 and 59, and should not be more than 10

percent 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 percent greater.

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 jio inch:

Pitch diameter tolerances for pitches finer than %o inch are to each other and to the tolerance for }4o inch as the 0.6th power of their respective pitches.

Pitch diameter tolerances for pitches coarser than ]4o inch are to each other and to the tolerance for y2 o inch as the 0.9th power of their respective pitches.

The exponent 0.6 was chosen for pitches finer than }io 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.

(b) Tolerances for Screw Threads of Special Diameters, Pitches,

and Lengths of Engagement.—As stated in section V, the pitch diameter

tolerances for special sizes of threads of American National form as given in tables 36, 37, 38, and 39 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 60.

Inch Class 1, loose fit Class 2, free fit.

0. 0045

. 0030

. 0020

. 0010

Class 3, medium fit Class 4, close fit

127
128 NATIONAL SCREW THREAD COMMISSION

Table 60.

Schedule of tolerance increments for special threads

nioqc nf fit Diameter

increment Length of engagement

increment

Pitch in- crement

1 2 3 4

Class 1, loose fit 0.002^

.002^

.002V-P

.001V-0

0. 002 Q

.002Q

.002Q

. 001Q

0.020 Vp

.010 Vp

.005 Vp

.0025Vp

Glass 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 6*f engage- ment and its diameter equivalent is as follows: E' = (±p') cot a

in which

E' =pitch diameter increment due to lead error p

f =the maximum lead error between any two of the threads engaged

a =half angle of thread The quantity E' 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

E' = l. 7321 p

r

(b) Diameter Equivalent of 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: cot a'=nr,—-. ±cot a E sin a cos a

in which

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 In solving for E" the average value of a' for the two sides of the thread, regardless

of their signs, should be taken. 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:
WIEE METHODS OF MEASUREMENT 129

For threads of American National form this formula reduces to

cot a =2^77

or #" = 1.5 v tan a' For the form of thread recommended for pipe-thread gages the formula becomes

, 1. 53812p

cot a — —

or

1.53812,. E"= tan a' n 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 44. 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 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 "best-size" wire for that pitch.

Any size, however, may be used which will permit 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 variation 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 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:

(x =^sec a

in which

G= diameter of wire p =pitch

included angle of thread

This formula reduces to

G=0.57735Xp, for 60° threads

It is frequently desirable, as, for example, when a best-size wire is not available, to measure pitch diameter by means of wires of other than the best size.
130 NATIONAL SCREW THREAD COMMISSION

The minimum size which may be used is limited to that permitting the wire to 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

creast of the thread. The diameters of the best size, maximum, and minimum

wires for American National coarse, fine, hose-coupling, and pipe threads are given in tables 61 and 62.

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

Figure 44.

Three-wire method of measuring pitch diameter of thread plug gages. 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 as determined by measurements under stand- ard conditions as specified below.

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 as determined by measure- ments under standard conditions as specified below, 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.
WIRE METHODS OF MEASUREMENT 131

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

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 14 to 16 ounces is recommended. For pitches

of 20 threads per inch and coarser a pressure of 2% to 2% 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 cannot be expected.
132 NATIONAL SCREW THREAD COMMISSION

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+~^-G (1+cosec a) 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 formerly given in 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

E

O 86603 n For a given set of best-size wires E=M-X

when

•tr VY/1 i \ cot a X~G (1+ cosec a) 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

°°2r^

^or s*an(*ard pitches are given in table 61.

1 The general formula, in which the helix angle is taken into account, is: E=MJr~~ —G(l+cosec a+^r 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 .UWE 3.1416 NE

in which i=lead N=number of turns per inch E=nominal pitch diameter -g— cos a cot a) 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. The 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 formula except when the value of the term cos a cot exceeds 0.00015 inch, as in the case of Acme

and multiple threads, or other threads having exceptionally large helix angles.
WIRE METHODS OF MEASUREMENT 133

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

Figure 45.

Measurement of -pitch diameter of taper thread gages hy the 3-wire method. shown in figure 45 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. Measure- ment 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. 45.) 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 thread plug gage, the
NATIONAL SCREW THREAD COMMISSION

Figure 46.

•Measurement of pitch diameter of taper thread gages by the 2-wire method.
WIRE METHODS OF MEASUREMENT 135

threads of which are symmetrical with respect to a line perpendicular to the axis, then has the form: J E=M sec V +^~ — G (1+cosec a) in which

E=pitch diameter

M=measurement over wires

2/ = half angle of taper of thread n—number of threads per inch=l/p

a = half angle of thread G= diameter of wires 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 for- mula:

E=l. 00049 M+0. 86603 p-SG

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. In recent years measuring machines have replaced micrometer calipers generally

for the measurement of taper thread plug gages, and the following method, illus- trated in figure 46, is applied: This method 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 to be

correct, it is more accurate. The axis of the gage and the line of measurement

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 46 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 measurement is taken over

the two wires; the second wire is then moved to the thread 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 1.00049 M.

6. MEASUREMENT OF PITCH DIAMETER OF THREAD RING GAGES

The application of direct methods of measurement to determine the pitch

diameter of thread ring gages presents serious difficulties, particularly in securing 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.

2 See footnotes 18 and 1, pp. 100, 132. In the above formula for the value of E, the term is an approxi- mation for the value of H. The exact value of H is used when the value of the term

taD

° exceeds

0.00004 inch, which ordinarily occurs only on special taper threads of coarse pitch or steep taper. Also the

multiplication of the measurement over the wires by the secant of the half angle of the taper of the thread is not an exact correction for the inclination of the measurement. The complete formula is— „ , cot a -tan2

(/ tan a . ,S2

. , E = (Ai— G) sec iM G (cosec a cos a cot a) This formula gives a value of E which is 0.000081 inch smaller than that given by the simplified formula for the 2^>-inch-8 American National taper pipe thread, the worst case in this thread series.
136 NATIONAL SCREW THREAD COMMISSION

Table 61.

Wire sizes and constants, American National coarse, fine, hose-coupling,

and pipe threads

Wire sizes 1 Threads

per inch n

Pitch Pitch

2 Depth of V thread Best

0.577350p Maximum1.010363p Minimum0.505182p

1 p=- V i 2 2n

cot 30°

271

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

56

48

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

44

4036

32

28

. 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

2724

20

18

16

. 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

1312rm

11

. 07143

. 07692

. 08333

. 08696

. 09091

. 03571

. 03846

. 04167

. 04348

. 04545

. 06186

. 06662

. 07217

. 07531

. 07873

. 05773

. 06415

. 07217

. 07698

. 08248

. 10104

. 11226

. 12630

. 13472

. 14434

. 05052

. 05613

. 06315

. 06736

. 07217

109

8

7

. 10000 .11111

. 12500

. 13333

. 14286

. 05000

. 05556

. 06250

. 06667

. 07143

. 08660

. 09623

'. 10825

. 11547

. 12372

. 09623

. 11547

. 12830

. 14434

. 16839

. 20207

. 22453

. 25259

. 08420

.10104

. 11226

. 12630

65m4

. 16667

. 20000

. 22222

. 25000

. 08333

. 10000 .11111

. 12500

. 14434

. 17321

. 19245

. 21651

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.
WIRE METHODS OF MEASUREMENT

e

©

1 !

;

! 1 1 1 III ' III II X®

X i i

! ! ! : : 1 j 1 II i i i i i III II iii ix ®X

>o

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CO

i i ! ! i ! ! II ill i i III II | |

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1

!. I

! ! i i ! ! ! i II ix® xxx i

i ; i ! !

,' i i ! ! ! ! M II <®x XXx i

00

i f; ; ; III II III 1 III

X<?5XX XX

I

i i ! ! ! i : i i i i III II | |

| X®XXX x ; I j o

i j II II III II jX ®XXXX X j

i S j j II.

i I : i><x® xxxxx |

;

i i i i Ill II : i i x ><®X XXXXX |

j

i i i ! II i i i i 1 I x€5>XX xxxxx |

j

CO

i

,' i

;' i i i i X®XXX xx>CX ; ; ;

23 II II ; : i i

i

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CO

; i i : i i X® XXXXX X ;

00 M : i i i x <8>x xxxxx ;

i oCN i i | j II II® XX xx> \ | i

! !

CN II |

| x®xxx x j

CM i i i 1 |x ®xxxx | i

i i 3

1 1 i 1® XXX x i i i

CO

i

i i i : x®X XXX

COCO

1

:' i i x®XX XX | 1 1 oTt<

| ; X®XXX XX ;

t£ ;X ®xxxx x ; ;

00

|<8> XXXXX ; ;, ; -1 Mi ®x XXX

CO |x®xx XX i

<NI> X0XXX x i o00 ®xxxx ; i ;

inches)

I

).

00722

.

00802

).

00902

.

UiUdl

.

....

_

.01203 .01312 ).

01443 ).01604

.

01804

).

02062 ).

02138 ).

02406 ).02887 ).03608 ).

04124 ).04441 ).04811

>.

05020

).

05249 ).

05773 ).05415 ).07217

.

07698

.08248 ).

09623 ).11547

.

14434

182129—33 o o © o o

-10 ooooo ooooo ooooo ooooo oooo
138 NATIONAL SCREW THREAD COMMISSION

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 3-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 3-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 M—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 £=p/4

and the thread angle being 29°, the above formula reduces to

i=1.12931p + 0.25862(M-.D)-G(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 63. Also, for convenience in carrying out computations, the values of 1.12931p and of 1.29152 + 0.48407$ 2 for various diameters and pitches of single, double, triple, and quadruple threads are given

in tables 64, 65, 66, and 67. Table 63.

Wire sizes and constants, American National Acme threads (29°)

Pitch Wire sizes 1 Threads per inch 1 " n Best

0.516450p Maximum,0.650013p Minimum,

0.487263p

1 2 3 4 5

1 - Inch

1. 00000 Inch

0. 51645 Inch0. 65001 Inch0. 48726 1H— . 75000 . 38734 . 48751 . 36545 1H . 66667 . 34430 . 43334 . 32484

2 . 50000 . 25822 . 32501 . 24363 2H . 40000 . 20658 . 26001 . 19491

3 . 33333 . 17215 . 21667 . 16242

4 .25000 . 12911 . 16250 . 12182

5 . 20000 . 10329 . 13000 . 09745

6 . 16667 . 08608 . 10834 . 08121 8.— . 12500 . 06456 . 08125 . 06091

10 . . 10000 . 05164 . 06500 . 04873

12 . 08333 . 04304 . 05417 . 04061 14 . 07143 . 03689 . 04643 . 03480

16 . 06250 . 03228 . 04063 .03045

1 Based on zero helix angle.
WIRE METHODS OF MEASUREMENT 139

Table 64.— Values of 1.12931? and 1.29152 + 048407S 2 for various diameters and

pitches, Acme threads SINGLE THREADS

12 | 10 • 2H • m m

1.129313?

0. 09411 0. 11293|o. 14116 0. 18822 0. 22586 0. 28233|o. 37M4|o. 45172 0. 56465|o. 75287 0. 84698 1. 12931

Threads per inch, n = l/p

1. 291518+0. 484074S2

1. 29458

369 1. 29478

314 394 1. 29552

277 339 300458 252 394

233 272 348

220 252 314

288

1. 29458 209 236 408

201 224 268 369 1. 29478

194 214 252 339 432

189 206 239 314 394

181 194 220 277 339 1. 29458

175 186 206

196 252 300 394

171 168

180 233 272 348

175 189 220 252 314

288

1. 29458

165 172 183 209 236 408

163 169 179 201 224 268 369 1. 29478

1 AO 10.4 1 A7 10/ 1 7^ I/O 194 214 i.OL AQ1 161 165 172 189 206 239 314 394

160 163 170 184 200 228 294 364

159 162 168 181 194 220 277 339 1. 29458

158 161 166 178 190

186 212 264 318

OUU

423

10/ 160 165 175 206 394

157 159 163 173 183 201 242 285 369

156 159 162 171 169 180 196 233 272 348

156 158 161 177 192 226 261 330

156 157 161 168 175 189

186 220 252 314 1. 29458100 157 i fin 10U 10/ 173 I/O Z14 244 inn OUU 4Q1 10

1

155 157 159 165 172 183 209 236 288 4C8

155 156 159 164 170

169

181 205 230 277 387

155 156 158 163 179 201 224 268 369 1. 29434

154 156 158 163 168 177 197 219 259 353

ooy

413

lot 155 157 162 1 A7 10/ 17K 1 / O L\fi 91 A 252

154 155 157 161 166 174 191 210 245 326 377

154 155 157 161 165 172 189 206 239 314 362

154 155 156 160 164 171 187 203 233 303 348

154 155 156 160 163 170 184 200 228 294 336

154 154 156 ioy 163 169 183 197 994 285 324

154 154 156 159 162 168 181 194 220 277 314 1. 29458

153 154 155 158 161 167 179 192 216 270 305 440

153 154 155 158 161 166 178 190 212 264 296 423

153 154 155 158 160 165 176 188 209 257 288 408

153 154 155 157 160 165 175 186 206 252 281 394

153 154 155 157 159 163 173 183 201 242 268 369

153 153 154 156 159 162 171 180 196 233 257 348

153 153 154 156 158 161 169 177 192 226 247 330

153 153 154 156 157 161 168 175 189 220 239 314

153 153 154 155 157 160 167 173 186 214 232 300

153 153 154 155 157 159 165 172 183 209 225 288

153 153 154 155 156 159 164 170 181 205 220 277

152 153 153 155 156 158 163 169 179 201 215 268

152 153 153 154 156 158 163 168 177 197 210 259

152 153 153 154 155 157 162 167 175 194 206 252

152 153 153 154 155 157 161 166 174 191 203 245

152 153 153 154 155 157 161 165 172 189 199 239

152 153 153 154 155 156 160 164 171 187 196 233 152 152 153 154 155 156 160 163 170 184 194 228

152 152 153 154 154 156 159 163 169 183 191 224

152 152 153 154 154 156 159 162 168 181 189 220

152 152 153 153 154 155 158 161 167 179 187 216

152 152 153 153 154 155 158 161 166 178 185 212

152 152 153 153 154 155 158 160 165 176 183 209

1. 29152 1. 29152 1. 29153 1. 29153 1. 29154 1. 29155 1.29157 1. 29160 1. 29165 1. 29175 1. 29182 1. 29206
140 NATIONAL SCREW THREAD COMMISSION

Table 65.

Values of 1.12931-p and 1 .29152+0. 48407S 2 for various diameters and

pitches, Acme threads DOUBLE THREADS

Basic major

diameter

(inches)

H—

Vl6- Y2-

/l6. HH--

13/16 V8-

15/l6 1... m.

1H- m.

154- VA.

2 .... 2H- 2H256- 2H25/6. 294. VA. 8—

3H31/4. 356_ 3H356. 3%.

374-

4___

41-6. 4H456- 4J4_

456-

454-

477 6_ 5__.

5^4. 5H554- 6_-.

6J4- 6^-

654. 7—

7i/4- 7H754- 8—

8J4- 8H854. 9—

9i/4- m~

954- 10-

Threads per inch, n=l/p

12 10 8 6 i | 3 2H IH > 1.12931©

0. 0941l|0. 11293|o. 14116 0. 18822 0. 22586|o. 28233 0. 37644 0. 45172 0. 56465 0. 75287 0. 84698 1. 12931

.

1.291518+0.484074S*

1. 32291 L 31009

1. 30378

1. 34056

1. 31999

1. 31009

1. 37871

1. 34056

1. 32291 1. 35558

1. 30021

1. 29800

654 552

478

423

381 348

322

300

268

245

228

1. 30458

1. 30121

1. 29899

745

635 552 489

440

401 369

322

288

264

1. 31332

1. 30753

1. 30378

1. 30121

1. 29937

800

697

616 552

501 423

369

330

1. 33496

1. 32291

1. 31525

1. 31009

1. 30645

1. 30378

1. 30177

1. 30021

1. 29899 800

654

552

478

1. 36041

1. 34056

1. 32820

1. 31999

1. 31425

1. 31009

1. 30698

1. 30458

1. 30271

1. 30121

1. 29899

745 635

1. 37871

1. 35558

1. 34056

1. 33027

1. 32291

1. 31746

1. 31332

1. 31009

1. 30753

1. 30378

1. 30121

1. 29937

1. 37188

1. 35558

1. 34378

1. 33496

1. 32820

1. 37519

1. 36041

1. 34923

1. 322911 1. 34056

1.31525 1. 32820

1. 37871

1. 35558

.

1. 31009

1. 30645

1. 31999

1. 31425

1. 34056

1. 33027 1. 37188 216 245 300 423 552 800 1. 30378 1. 31009 1. 32291 1. 35558 1. 37871 206 231 277 381 489 697 I. OUl / / 1. 30698 1. 31746 1. 34378 1. 36215

198 220 259 348 440 616 1. 30021 1. 30458 1. 31332 1. 33496 1. 34989

192 211 245 322 401 552 1. 29899 1. 30271 1. 31009 1. 32821 1. 34057

187 203 234 300 369 501 800 1. 30121 1. 30753 1 32291 1. 33331 1. 37871

183 197 224 283 343 458 72C 1. 29999 1. 30547 1. 31868 1. 32755 1. 36581

180 192 216 268 322 423 654 899 1. 30378 1. 31525 1. 32291 1. 35558

177 188 209 256 303 394 599 815,1.30238 1. 31244 1. 31911 1. 34732

174 184 203 245 288 369 552 745 1. 30121 1. 31009 1. 31596 1. 34056

172 181 198 236 275 348 513 686 1. 30021 1. 30812 1. 31332 1. 33496- 170 179 194 228 264 330 478 635 1. 29937 L 30645 1. 31108 1. 33027

169 176 191 222 254 314 449 590 864 1. 30502 1. 30917 1. 32630

167 174 187 216 245 300 423 552 800 1. 30378 1. 30753 1. 32291

166 173 184 211 238 288 401 519 745 1. 30271 1. 30611 1.31999

165 171 182 206 231 277 381 489 697 1. 30177 1 30487 1. 31746: 164 170 180 202 225 268 364 463 654 1. 30094 L 30378 L 31525- 163 168 178 198 220 259 348 440 616 1. 30021 1. 30282 1. 31332

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

161 165 173 190 207 239 310 384 525 847 1. 30053 1 30874

160 164 172 187 203 234 300 . 369 501 800 1. 29992 L 30753

160 164 170 185 200 228 291 356 478 758 937 1. 30645

159 163 169 183 197 224 283 343 458 720 887 1. 30547

159 162 168 181 195 220 275 332 440 686 842 1. 30458

159 162 167 180 192 216 268 322 423 654 800 1. 30378

158 161 167 178 190 212 261 312 408 625 763 L 30305

158 161 166 177 188 209 256 303 394 599 728 1. 30238

158 160 165 176 186 206 250 295 381 575 697 1. 30177

157 160 164 174 184 203 245 288 369 552 668 1. 30121

157 159 163 172 181 198 236 275 348 513 616 1. 30021

156 158 162 170 179 194 228 264 330 478 572 1. 29937

156 158 161 169 176 191 222 254 314 449 534 864

156 157 160 167 174 187 216 245 300 423 501 800

155 157 160 166 173 184 211 238 288 401 472 745

155 157 159 165 171 182 206 231 277 381 446 697

155 156 159 164 170 180 202 225 268 364 423 654

155 156 158 163 168 178 198 220 259 348 403 616

154 156 158 162 167 176 195 215 252 334 385 582

154 155 157 162 166 174 192 211 245 322 369 552

154 155 157 161 165 173 190 207 239 310 355 525

154 155 157 160 164 172 187 203 234 300 342 501

154 155 156 160 164 170 185 200 228 291 330 478

154 155 156 159 163 169 183 197 224 283 319 458

154 154 156 159 162 168 181 195 220 275 309 440

153 154 156 159 162 167 180 192 216 268 300 423

153 154 155 158 161 167 178 190 212 261 292 408

153 154 155 158 161 166 177 188 209 256 284 394

153 154 155 158 160 165 176 186 206 250 277 381

1. 29153 I. 29154 1. 29155 1. 29157 1. 29160 1. 29164; 1. 29174

1

1. 291841. 29203 1. 29245 1. 29271 1. 29369
WIRE METHODS OF MEASUREMENT 141

Table 66.— Values of 1.12981? and 1.89152+048407S* for various diameters and

pitches, Acme threads TRIPLE THREADS

Threads per inch, n = l/p

12 » 6 5 » 2^ m 1H 1 1.12931p

0. 09411 0. 11293 0. 14116 0. 18822 0. 22586|0. 28233 0. 37644 0. 45172 0. 56465 0. 75287|o. 84698 1. 12931 1.291518+0.484074S2

I 1. 4018711.48771 1.35558 1.40187

1. 33331 1. 36215 1.320921.34057

1.313321.32755

1.308321.31911

X. OOOOl. 1.31911

1. 31108

1. 30611

X. 0\J404

X. OVJVJUO

1. 29887

763

668

593

534 486

413 362 324

1. 43565

1. 38927

1. 36215

1. 34492

1. 33331 L 32511

1.31911

1. 31458

1. 31108

1. 30832 L 30611

1. 30282

1. 30053

1. 29887

1. 44653

1. 40187

1. 37406

1. 35558 L 34267

1. 33331

1. 32630

1. 32092

1 31669 L 31332

1. 30832

1. 30487

1. 30238

-------

1. 48771

1. 43566

1. 40187

1. 37871

1. 36215

1 QAQfiO i. o^tyoy

1. 34057

1. 33331

1. 32755

1. 31911

1. 30918

1. 30487

1. 30238

1. 30053

1. 29911 800 712

641

534 458

403

1. 31332

1. 30918

1. 30611

1. 30378

1. 30197

1. 30053

1. 29937

763

641 552

1. 47233

1. 43566

1. 40911 1. 47978

1. 38927 1. 44653

1. 3740611. 42137

1. 36215

1. 34492

1. 33331

1. 32511

11.

1.

1.

40187

37406

35558

34267

1

11

1

48771 43566 40187

37871 1. 47233

296 362 486 763 1. 30053 1. 30611 1. 31911 1 33331 1 36215 X. 1. 48771 274 33C 434 668 1. 29911 1. 30378 1. 31458 1. 32630 1 34989 1.40911 L 45043

257 305 394 593 800 1. 30197 1. 31108 1. 32092 1 34057 1. 38927 1. 42285

243 284 362 534 712 1. OUUOO 1. 30832 1. 31669 1 33331 1. 37406 1. 40188

232 268 336 486 641 1. 29937 1. 30611 1. 31332 1 32755 I. 36215 1. 38555 1. 48771

222 254 314 446 582 842 1. 30431 1. 31058 1 32291 1. 35263 1. 37260 1X. 4^868 ^UOLtO 215 243 296 413 534 763 1. 30282 1. 30832 1 31911 1. 34492 L 36214 1. 43566

208 233 281 385 493 697 1. 30158 1. 30645 1 31596 1. 33858 1. 35359 1. 41708

203 225 268 362 458 641 1. 30053 1. 30487 1 31332 1. 33331 1. 34650 1. 40187

198 218 257 342 429 593 1. 29963 1. 30353 1 31108 1. 32887 1. 34056 1. 38927

194 212 247 324 403 552 887 1. 30238 1 30918 1.32511 1. 33554 L 37871

190 207 239 309 381 517 820 1 30139 1 30753 1. 32189 L 33125 L 36977

187 203 232 296 362 486 763 1. o\j\joo 1 30611 1.31911 1. 32755 1. 36215

184 199 225 284 345 458 712 1. 29977 1 30487 1. 31669 1. 32435 1. 35558

182 195 220 274 330 434 668 911 1 30378 1. 31458 1. 32156 X. O^i/OiJ 179 192 215 265 316 413 628 852 1 30282 1. 31272 1. 31911 1. 34493

177 18S 210 257 305 394 593 800 1 30197 1. 31108 L 31694 L 34056

176 186 206 250 294 377 562 754 1 30121 1. 30962 1. 31502 1. 33672

174 184 203 243 284 362 534 712 1 30053 1. 30832 1. 31332 1. 33331

173 182 199 237 276 348 508 675 1 29992 1. 30716 1. 31179 X. OOv^J

171 180 196 232 268 336 486 641 937 1. 30611 1. 31041 1 32755

170 178 194 227 261 324 465 610 887 1.30516 L 30917 L 32511

169 177 191 222 254 314 446 582 842 1. 30431 1. 30805 1. 32291

168 175 189 218 248 305 429 557 800 1. 30353 1. 30704 1. 32091

167 174 187 215 243 296 413 534 763 1. 30282 1. 30611 1 31911

166 173 185 211 238 288 399 513 738' 1. 30217 X, OwiU 1 31746

166 172 183 208 233 281 385 493 697 1. 30158 1. 30449 ll 31595

165 171 182 205 229 274 373 475 668 1. 30103 1. 30378 1 31458

164 170 180 203 225 268 362 458 641 1. 30053 L 30313 1. 31332

163 168 177 198 218 257 342 429 593 1. 29963 1. 30197 1. 31108

162 167 175 194 212 247 324 403 552 887 1. 30097 1. 30918

161 165 173 190 207 239 309 381 517 820 1. 30011 1. 30753

160 164 171 187 203 232 296 362 486 763 1. 29937 1. 30611

160 163 170 184 199 225 284 345 458 712 871 1. 30487

159 162 168 182 195 220 274 330 434 66§ 814 1. 30378

159 162 167 179 192 215 265 316 413 628 763 1. 30282

158 161 166 177 189 210 257 305 394 593 717 1. 30197

158 160 165 176 186 206 250 294 377 562 677 1. 30121

157 160 164 174 184 202 243 284 362 534 641 1. 30053

157 159 163 173 182 199 237 276 348 509 608 1. 29991

157 159 163 171 180 196 232 268 336 486 579 937

156 158 162 170 178 194 227 261 324 465 552 887

156 158 162 169 177 191 222 254 314 446 528 842

156 158 161 168 175 189 218 248 305 429 506 800

156 157 160 167 174 187 215 243 296 413 486 763

155 157 160 166 173 185 211 238 288 399 467 728

155 157 160 166 172 183 208 233 281 385 450 697

155 156 159 165 171 182 205 229 274 373 434 668

1. 29155 1. 29156 1. 29159 1. 29164 1. 29170 1. 29180 1. 29202 1. 29225 1 29268 1. 29362 1. 29420 1. 29641
142 NATIONAL SCREW THREAD COMMISSION

Table 67.Values of 1.12981$ and 1.29152 + 048407S 2 for various diameters and

pitches, Acme threads QUADRUPLE THREADS

Basic major

diameter

(inches)

Threads per inch, n = l/p IS 10 8 6 | 5 3 2*4 2 1*4 m i 1.12931p

0. 09411 0. 11293 0. 14116|o. 18822 0. 22586 0. 28233 0. 37644|o. 45172 0. 56465 0. 75287 0. 84698|l. 12931 1.291518+0.484074S2 n 1. 41708

1. 36582

1. 34057

1. 62060

1. 31746

1. 48771

1. 40540

1. 36581

1. 3437S

1. 33027

1. 32139

1. 31525

1. 31083

1. 30753

1. 64030

1. 48771

1. 41708

1 9.7Q71

1. 35558

1. 34056

1. 33027

1. 32291

1. 31746

1. 31332

1. 31009

1. 30753

1. 30547

1. 60160

1. 30021

1. 29864

745 654

582

525

MeH— 1. 54776

1. IOO0U

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. 2,\)\)67 831

y\6 1. OD/ 1U

1. 48771

1. 43827

1. 40540

1. 38246

1. 36581

1. 35335

1. 34378

1. 33627

1. 33027

1 901 9fi 1. 31525

1. 31083

1. 30753

1. 30502

1 9fi9fi£

1. 6O6O0

1. 30148

*4 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 91 fififi 1. oiuuy

1. 30753

946— 1.31161 % 1. 30753

1. 30458

1. 6026a

1 VlQ 1. 61295

1. 54777

1. 50057

1. 46531

6A13/l6 1. 30069

1. 29937

1. 30502

1. 30305

1. 30148

1. 30021

1 OO.C91

1. 2\)o6l 697

599 525 468

423 387

1, 62621

7A 1. 56710

15Ae 831 745

616

525

458 408

369

339 314

1. 43827

1. 41708

1 9QA/1A 1. oUO'iD

1. 36581

1. 35124

1. 34056

1. 33252

1. 6Z06U

1. 32140

1. 52237

1. 48771

1 43826

1. 4054C

1. 38246

1. 36581

1. 35335

1 34378

l! 33627

1 1. 64030

1 54776

1.' 48771

1. 44653

1. 41708

1. 39529

1 37871 L 36581

1*4

i

3A 1. 61295

1. 54776

1. 50056

1. 46530

1. 43827

1*4 1. 64030

1

5A 1. 57403

1 3/a 1. 52499

l 1. 48771 7A

2 294 358 478 745 1. 30021 1. 30547 1. 31746 1. 33027 1. 35558 1. 41708 1. 45868 1. 64030 2A 277 334 440 675 1. 29917 1. 30378 1. 31425 1. 32540 1. 34732 1. 40017 1. 43566 1. 58870

2*4 263 314 408 616 831 1. 30238 1. 31161 1. 32139 1. 34056 1. 38646 1. 41708 1. 54776

252 297 381 567 758 1. 30121 1 9fifi/ffi 1. ouy<±u 1. oloUO 1 99AOA 1. ooiyo 1. 37519 1. 40187 1 K1A79 1. 014/

O

2*4 242 283 358 525 697 1. 30021 1. 30753 1. 31525 1. 33027 1. 36581 1. 38927 1. 48771

2

5A 233 270 339 489 644 1. 29937 1. 30595 1. 31287 1. 32630 1. 35793 1.37871 1. 46530

2

SA 226 259 322 458 599 864 1. 30458 1. 31083 1. 32291 1. 35124 1. 36977 1. 44653

2

7A 220 250 307 431 559 800 1. 30341 1. 30907 1. 31999 1. 34551 1. 36215 1. 43064

o 214 242 294 408 525 745 1 9A19C 1. 6026o 1. 30753 1 917/1/?

1. ol/4o 1. 34056 1. 35558 1. 41708

3*£ 209 235 283 387 495 697 1. 30148 1. 30619 1. 31525 1. 33627 1. 34989 1. 40540

3*4 205 228 272 369 468 654 1. 30069 1. 30502 1.31332 1. 33252 1. 34493 1. 39529 3% 201 223 263 353 444 616 1. 29999 1. 30397 1.31161 1. 32922 1. 34056 1. 38647

3*4 197 218 256 339 423 582 937 1. 30305 1. 31009 1. 32630 1. 33672 1. 37871

6°/% 194 213 248 326 404 552 881 1. 60222 1 9/107/1

1. ,30874 1. 32371 1. 33331 1 9 71 CO1. o/loa 3% 191 209 242 314 387 525 831 1. 30148 1. 30753 1.32139 1. 33027 1. 36581 3% 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*i 184 199 226 285 346 458 708 1. 29967 1. 30458 1. 31578 1. 32291 1. 35124

183 196 222 277 334 440 675 917 1. 30378 1. 31426 1. 32091 1. 3473/ 4% 181 194 218 270 324 423 644 872 1. 30305 1. 31287 1. 31911 1. 34377

4*4 179 191 214 264 314 408 616 831 1. 30238 1. 31161 1. 31746 1. 34056

ty& 178 189 211 257 305 394 591 793 1. 30177 1. 31045 1. 31595 1. 33764 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

5*4 172 181 197 233 270 339 489 644 1. 29937 1. 30595 1. 31009 1. 32630 5*4— 170 178 193 226 259 322 458 599 864 1. 30458 1. 30832 1. 32291

5?4 169 176 190 220 250 307 431 559 800 1. 30340 1. 30680 1. 31999

6 167 174 187 214 242 294 408 525 745 1. 30238 1. 30547 1. 31746

6*4 166 172 184 209 235 283 387 495 697 1. 30148 1. 30431 1. 31525

6*4 165 171 181 205 228 272 369 468 654 1. 30069 1. 30329 1.31332 m 164 169 179 201 223 263 353 444 616 1. 29999 1. 30238 1.31161

7 163 168 177 197 218 256 339 423 582 937 1. 30157 1. 31009

7*4 162 167 175 194 213 248 326 404 552 881 1. 30086 1. 30874

7*4 162 166 174 191 209 242 314 387 525 831 1. 30021 1. 30753

73/4 161 165 173 189 205 236 303 372 501 786 1. 29963 1. 30644

8 160 164 171 187 202 231 294 358 478 745 , 911 1. 30547

8*4 160 163 170 184 199 226 285 346 458 708 863 1. 30458

8*4 159 163 169 183 196 222 277 334 440 675 821 1. 30378

834 159 162 168 181 194 218 270 324 423 644 781 1. 30305

9 159 162 167 179 191 214 264 314 408 616 745 1. 30238

9*4 158 161 166 178 189 211 257 305 394 591 712 1. 30177 9*4— 158 161 166 176 187 208 252 297 381 567 682,1. 30121

93/4 158 160 165 175 186 205 247 289 369 545 6541.30069

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
CONTROL OF ACCURACY IN PRODUCTION 143

APPENDIX 3. CONTROL OF ACCURACY OF THREAD ELEMENTS IN THE PRODUCTION OF THREADED PRODUCT

1. INTRODUCTION

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 common use. 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. Internal threads or tapped holes are commonly produced by means of taps

and sometimes by lathe tools. Much progress has been made in the standardization of the dimensions and tolerances for cut and ground thread taps. 3

2. 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.

(a) Control of Tooth Outlines.—Inspection of the angle and profile of the thread-forming tool is essential to control the accuracy of the thread produced.

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. 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

8 See Report No. B5e-1930, "Taps: Cut and Ground Threads" of the American Standards Association.
144 NATIONAL SCREW THREAD COMMISSION

to a magnification of 50 or 15 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 system free from distortion. Optical projection

machines and comparators are available for this work in commercial designs.

(See " Thread comparators," p. 151.) In table 68 are given useful data for drawing the charts for any standard pitch.

Table 68.Dimensions for determining shape of cutter, chaser, hob, or tap teeth American National coarse, fine, and hose coupling threads

Threads

per inch, n

Pitch, P HXp HXp HiXp

Depth

of thread h HXh R=%Xh YeXh HsXh

One

half pitch diameter

toler- ance

for class 2

fit, ViXT

h+YiXT

12

Inch

0.01250

. 01389

. 01562

. 01786

. 02083

. 02273

. 02500

. 02778

. 03125

. 03571

. 04167

. 05000

. 05556

. 06250

. 07143

. 07692

. 08333

. 08696

. 09091

. 10000

. 11111

. 12500

. 13333

. 14286

. 16667

. 20000

. 22222

. 25000

Inch

0. 00625

. 00781

. 00893

. 01042

.01136

. 01250

, 01389

.01562

, 01786

. 02083

, 02500

, 02778

, 03125

, 03571

, 03846

. 04167

. 04348

, 04545

, 05000

. 05556

, 06250

. 06667

, 07143

. 08333

, 10000

, 11111 12500

Inch

0. 00156

. 00174

. 00195

. 00223

. 00260

. 00284

. 00312

. 00347

. 00391

. 00446

. 00521

. 00625

. 00694

. 00781

. 00893

. 00962

. 01042

.01087

.01136

. 01250

. 01389

. 01562

. 01667

. 01786

. 02083

. 02500

. 02778

.03125

Inch

0. 00052

. 00058

. 00065

, 00074 00087

, 00095 00104

00116

. 00130

00149 00174

00208

00231 00260

00298

00321 00347

00362

00379

00417 00463

00521 00556

00595

Inch

0. 00812

. 00902

.01015 .01160

. 01353

. 01476

. 01624

. 01804

. 02030

. 02320

. 02706

. 03248

. 03608

. 04059

. 04639

. 04996

. 05413

. 05648

. 05905

. 06495

. 07217

.08119

Inch Inch

0. 00406 0. 00271

. 00451

. 00507

. 00580

. 00677

. 00738

. 00812

. 00902

.01015 .01160

. 01353

. 01624

. 01804

. 02030

. 02320

. 02498

. 02706

. 02824

. 02952

00833

00926 01042

, 09279

, 10825

. 12990

, 14434

. 16238

03608

04059

04330

04639 05413

06495

07217

08119

. 00301

. 00338

. 00387

. 00451

. 00492

. 00541

. 00601

. 00677

. 00773

. 00902

. 01083

. 01203 .01353

. 01546

. 01665

. 01804

. 01883

. 01968

. 02165

. 02406

. 02706

. 02887

. 03093

. 03608

. 04330

. 04811

. 05413

Inch

0. 00180

. 00200

. 00226

.00258

. 00301

. 00328

. 00361

. 00401

. 00451

. 00515

. 00601

. 00722

. 00802

. 00902

. 01031 .01110

. 01203

. 01255 .01312

. 01443

. 01604

. 01804

. 01925

. 02062

. 02406

. 02887

. 03208

. 03608

Inch

0. 00135

. 00150

, 00169

. 00193

, 00226

, 00246

00271

. 00301

. 00338

00387

00451 00541

00601 00677

00773

00833 00902

00941 00984

01083 01203

01353

01443 01546

01804 02165

02406

02706

Inch

0. 00045

.00050

. 00056

. 00064

, 00075

, 00082

. 00090

. 00100

,00113

, 00129

, 00150

. 00180

00200

, 00226

, 00258

, 00278

, 00301

, 00314

00328

00361

00401 00451

00481

00515

00601 00722

00802

00902

Inch

0. 00085

. 00090

. 00095

. 00100

. 00110

.00115

. 00120

. 00125

. 00135

. 00155

. 00165

. 00180

. 00205

. 00225

. 00245

. 00260

. 00280

1.00425

. 00295

. 00320

. 00350

. 00380

1 . 00800

. 00425

. 00505

. 00580

. 00635

. 00700 Based on hose-coupling thread tolerances.

(b) Control of Lead Errors.—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.

(I) 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 milling 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 cf 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 145

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, variations 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.

(2) 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.

When especially accurate work is required, as in producing threaded product to

class 4, close-fit specifications, it is very desirable, and sometimes necessary, that the feed of the tap or die be controlled by means of a lead screw. 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.

3. 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 when it is not practicable to apply other methods.

Various forms of single-point cutting tools for cutting threads of American

National form are illustrated in figure 47 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.
146 NATIONAL SCREW THREAD COMMISSION

(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

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 47 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 a 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 withdrawing 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 somefan DC = 7a./7 CL Sec V

fan V = fa*?S CoTo.

D

Figure 47.

Single point and multiple point thread cutting tools. times made to secure greater accuracy. Dies 4 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

* Simplified lists of sizes and varieties, for threads of American National form, of die-head chasers for self-opening and adjustable die heads, as adopted at general conferences of representative manufacturers,

distributors, and users, are promulgated in United States Department of Commerce Simplified Practice Recommendation R51-29.
CONTROL OF ACCURACY IN PRODUCTION 147

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.5 (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.6 4. ROLLING OF SCREW THREADS

The second general process for forming screw threads—namely, that of rolling

is a cold-forging process. It may be denned as an impression or displacement

method whereby the threads are formed by means of a die or roll having threads

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 percent

of the single depth of thread for small screws to 85 percent 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: A= VD2 -1.3Dp + 0.63^2 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. 7 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

6 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), vol. 113, Apr. 7, 1922, pp. 441-442, and discussion pp. 412-414.

6 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 the American Society of Mechanical Engineers, vol. 42, 1920, pp. 569-593; also the reference cited in footnote 5, for thread milling cutter profile.

7 This formula is derived in Size of Stock for Bolts Having Kolled Threads, by F. Webster. American

Machinist, vol. 30, Oct. 31, 1907, p. 630.
148 NATIONAL SCREW THREAD COMMISSION

the work with the necessary rigidity to withstand the heavy pressure, and to provide a bearing for the roll which will withstand the stress. 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 48, or radially as shown at B; a satisfactory thread is formed in either case.

(b) 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 48 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

SECTION ON AB.

Figure 48.

Methods of rolling screw threads. 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

ai=half angle of ridge of die a =half angle of thread to be rolled

s =helix angle of thread

The spacing of the ridges is determined by the formula

Px = p cos s in which

Pi— 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
CONTROL OF ACCURACY IN PRODUCTION 149

cylindrical segment. This method is used extensively for threading almost all forms of small and medium sizes of screws and bolts, when required in sufficiently

large quantities to warrant the use of a thread-rolling machine.8

5. 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 LAP

THRB.AD

A B

C

Figure 49.

Thread form of laps for lapping screw threads. 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

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

8 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, vol. 33, Apr. 21, 1910, pp. 739-741.
150 NATIONAL SCREW THREAD COMMISSION

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- 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 49.

6. 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

periodical tests of the tools, by periodical gaging of the product, and sometimes

by both. 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. Furthermore, 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 cannot be

taken as conclusive, and 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 wear on tools, etc.

(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. Thread snap gages are

to be preferred as "not go" gages. The cone-pointed snap gage usually has a single point on each side of the frame,

and is an effective "not go" gage. It does not, however, fully meet the require- ments for a "go" gage, as it does not check the lead, and, therefore, must be sup- plemented with some type of indicating gage to check the lead when used for checking pitch diameter, angle, and thread form. Also, as it checks only a single

diameter at a time, the "go" snap gage must be tried at a series of points to deter- mine 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 checks the lead for progressive, but not always for local or periodic lead errors, and, thus, it more

nearly fulfills the requirements for a "go" thread gage. This type or other types of short engagement are suitable for product of classes 4 and 5, provided

that an independent inspection of the lead is made.
GAGING PEACTICES 151

Thread snap gages having multiple toothed contact points, that is, toothed

blades, serrated or grooved plates, or grooved or threaded cylinders, are made in a

variety of forms, either as separate or combined "go" and "not go" gages. 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

for the less accurate classes of work, such as classes 1 and 2, and, if well designed

and accurately made, also for classes 3, 4, and 5.

(c) Thread Ring Gages.—'Thread ring gages are extensively used to inspect 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 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 lie 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 light, 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 tj^pes of optical thread comparators are applicable to external

threads. Two types of optical thread comparators for internal threads have

been developed by the Bureau of Standards, one know as an "optical coin- cidence thread gage", and the other as a "stereoscopic thread gage."9 (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.

(/) 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 fall below the minimum dimensions specified.

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

9 Described in B.S. Jour. Research, vol. 6, pp. 229-237, February 1931.
152 NATIONAL SCREW THREAD COMMISSION

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 hole. 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 combined as a "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 scale and

vernier or a 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. 10 APPENDIX 4. 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 % inch to 1^ 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.

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.

ii Methods of measuring pitch diameter of screw-thread gages are described in appendix 2, p. 129.
WRENCH FIT FOR THREADED STUDS 153

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 one

half 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 percent zinc dust, which has passed through a 200-mesh

sieve, and 60 percent 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 69. These

tolerances necessitate the use of ground-thread taps.

(e) The p

; tch diameter tolerances for the stud are as given in tables 69 and 70. They are the maximum variations permissible for each individual size of stud, as determined by the maximum and minimum interferences.

(/) Pitch diameter tolerances include angle variations but do not include lead

variations.

(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 (%X?>) at the root. It is equal to the measured pitch diameter of the stud minus the basic thread depth.

0') 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 class 2 nut.

0') 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 OkXp). 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.

(/c) 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.

182129—33 11
154 NATIONAL SCREW THREAD COMMISSION

(I) The tolerance on the minor diameter of a tapped hole of a given pitch is one sixth of the basic thread depth.

8. Illustration.—The relations of the maximum and minimum major,

pitch, and minor diameters of stud and tapped hole specified herein are shown in

figures 50, 51, and 52.

(b) CLASSIFICATION

1. Allowance and Tolerance Values.—Allowances and tolerances are

specified in tables 69 and 70, inclusive, for coarse-threaded and fine-threaded

Figure 50.

Illustration of tolerances, allowance, and crest clearances for class 5, wrench fit for threaded studs. 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 71 and 72 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.
WRENCH FIT FOR THREADED STUDS 155

TUD TAPPED

Figure 51.

Illustration of loosest condition for class 5, wrench fit for threaded studs, one-half inch, 13 threads, set in hard materials. NOTATION D = major diameter. E = pitch diameter. K = minor diameter,

ft = 0.0500 = basic thread depth.
156 NATIONAL SCREW THREAD COMMISSION

STUD " TA PPED

Figure 52.

Illustration of tightest condition for class 5, wrench fit for threaded studs, one-half inch, IS threads, set in hard materials. NOTATION D=major diameter. E=pitch diameter. K=minor diameter.

/i = 0.0500=basic thread depth.
WRENCH FIT FOR THREADED STUDS 157

Table 69.Class 5, wrench fit for threaded studs, allowances and tolerances for

studs and tapped holes, coarse threaded studs in hard materials

Sizes Threads

per inch

Interference on

pitch diameter

Mini- mumMaxi- mum

Pitch diameter

tolerances 1

Stud Tapped

holes

Errors in half angle consuming one

half of pitch di- ameter tolerances

Stud

54- Me

3 S. Me

Me%.

H.

7A-m

wm

m

Inch

0. 0003 .0005 .0005

.0006

.0007 .0008

.0008

.0009 .0010

.0011

.0011 .0012

.0012

.0013

Inch

0. 0018

.0040

.0045

.0050

.0055

.0060 .0060

.0065

.0065 .0065

.0065 .0065

.0065 .0070

Inch

0. 0007 .0020

.0024

.0026

.0029 .0032

.0031 .0033

.0031 .0027

.0024

.0023

.0017

.0021

Inch

0. 0008

.0015 .0016

.0018

.0019

.0020

.0021 .0023 .0024

.0027

.0030

.0030

.0036 .0036

Deg. Min

16

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 lead. (See "5. 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 tolerances 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, with the exception of the J4-mch size. Table 70.

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 di- ameter tolerances Mini- mum

Maxi- mum Stud Tapped

hole 2 Stud Tappedhole

1 2 3 4 5 6 7 8 Inch Inch Inch Inch Deg. Min. Deg. Min. u 28 0. 0005 0. 0034 0. 0018 0. 0011 58 35 Me 24 .0005 .0037 .0020 .0012 55 33 H - 24 .0006 .0044 .0026 .0012 1 11 33 Me . 20 .0006 .0044 .0025 .0013 57 30 X 20 .0007 .0050 .0030 .0013 1 9 30 Me... 18 .0007 .0050 .0028 .0015 58 31 M 18 .0008 .0055 .0032 .0015 1 6 31 H 16 .0008 .0059 .0035 .0016 1 4 29

74 14 .0008 .0061 .0035 .0018 56 29

l 14 .0009 .0069 .0042 .0018 1 7 29 m 12 .0009 .0067 .0038 .0020 52 28 IK 12 .0011 .0060 .0029 .0020 40 28 m 12 .0011 .0055 .0024 .0020 33 28 in — 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 lead. (See "5. 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 tolerances on

pitch diameter given in columns 5 and 6.

» The tolerances on the tapped hole given in column 6 are the same as those specified for class 4, close-fit screws and nuts.
158 NATIONAL SCREW THREAD COMMISSION

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WRENCH FIT FOR THREADED STUDS 159

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160 NATIONAL SCREW THREAD COMMISSION

5. 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 c f a slight difference in lead between stud

and hole is an advantage, especially with minimum pitch diameter interference.

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 minimum 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 r~ay 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 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 YsXp is sufficient. The use of thread micrometers or "go" thread snap gages of short engagement

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 cannot 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.
COMMON SCREW THREAD PRACTICE 161

APPENDIX 5. 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 73. Table 73.- -Common practice as to thread series and class of fit for screws, bolts, and nuts

Product Thread series Class of fit

Rough machine bolts Semifinished machine bolts: General applications Automotive vehicles Finished machine bolts: General applications Automotive vehicles Aircraft Machine screws Machine-screw nuts: Numbered sizes.. Fractional sizes. . Cap screws Stove bolts Carriage bolts Step bolts Button-head machine bolts. Set screws Threaded studs: Nut end__

Stud end Tap bolts Tap rivets

Coarse.

....doFine. Coarse

.

Fine... doCoarse or fine... do.

do.

doCoarse.

.do.

_do.

.do.

.do. '.-do

Fine

Coarse or fine. Coarse do

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. APPENDIX 6. AMERICAN NATIONAL ACME SCREW

THREADS (TENTATIVE SPECIFICATIONS)

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 herein.

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 op 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

half of the pitch.11

11 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. See p. 138.
162 NATIONAL SCREW THREAD COMMISSION

4. Clearance at Minor Diameter.—A clearance shall be provided at the minor diameter by making the minor diameter of the screw 0.010 inch smaller than basic for 10 or less threads per inch and 0.005 inch smaller than basic for more than 10 threads per inch.

5. Clearance at Major Diameter.—A clearance shall be provided 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 rounding of the corners of the threading tool and the side cutting action of milling cutters when these threads are milled. It will be necessary, 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 53.

Figure 53.

American National Acme form of thread. NOTATION A=2$° 00' 0=14° 30' p = pitch n=number of threads per inch N=number of turns per inch h=0.5p, basic depth of thread /= thickness of thread .F=0.37069p= basic width of flat

4. THREAD SERIES

For general purposes there has been selected a series of diameters and pitches

of Acme threads, listed in table 74, which are designated as standard. When it

is not feasible to use one of these sizes, it is recommended that, as far as practicable, some one of the pitches shown in table 75 be used; also, that the diameter

be within the range 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.
AMERICAN NATIONAL ACME SCREW THREADS 163

Table 74.American National Acme general purpose thread series

Identification Basic diameters Thread data

Sizes Threadsper

inch

IVIajor

eter,

Pitch

eter,

IVIinor

eter, Pitch P

Thread

thickness

at pitch

Basic depth of thread, Depth of thread with

Basic width

of flat, F=

Helix

angle

at basic pitch D E K line ft = 0.5 p clearance

0.37069p diameter,

8

1 2 3 4 5 g 7 g 9 10 11 Inches Inches Inches Inch Inch Inch Inch Inch Beg. Min. H 16 0. 2500 0. 2187 0. 1875 0. 06250 0. 03125 0. 03125 0. 03625 0. 0232 5 12 Me 14 .' 3125 . 2768 . 2411 . 07143 '. 03571 . 03571 . 04071 . 0265 4 42 %

~"

12 '. 3750 . 3333 '. 2816 . 08333 . 04167 . 04167 . 04667 . 0309 4 33

"fte 12 !4375 !3958 !3541 '. 08333 '. 04167 ! 04167 '. 04667 !o309 3 50 & 10 .5000 .4500 .4000 . 10000 . 05000 . 05000 . 06000 .0371 4 3 % g . 6250 . 5625 . 5000 . 12500 . 06250 . 06250 . 07250 . 0463 4 3 % g . 7500 . 6875 . 6250 . 12500 . 06250 '. 06250 ° 07250 '. 0463 3 19 % 8 !8750 !8125 !7500 ! 12500 ! 06250 ! 06250 ! 07250 !0463 2 48

5 1. 0000 . 9000 . 8000 20000 . 10000 . 10000 . 11000 . 0741 4 3 m 5 l! 1250 L 0250 !9250 . 20000 ! ioooo ! ioooo ! nooo !0741 3 33 VA 5 1. 2500 1. 1500 1. 0500 . 20000 . 10000 . 10000 . 11000 .0741 3 10 m 5 1. 3750 1. 2750 1. 1750 . 20000 . 10000 . 10000 . 11000 .0741 2 52 m- 4 1. 5000 1. 3750 1. 2500 . 25000 . 12500 . 12500 . 13500 .0927 3 19 W- 4 1. 7500 1. 6250 1. 5000 . 25000 . 12500 . 12500 . 13500 .0927 2 48 2 4 2. 0000 1. 8750 1. 7500 . 25000 . 12500 . 12500 . 13500 .0927 2 26 2J4 2 2. 5000 2. 2500 2. 0000 . 50000 . 25000 . 25000 . 26000 .1853 4 3

3 2 3. 0000 2. 7500 2. 5000 . 50000 . 25000 . 25000 . 26000 .1853 3 19 4 2 4. 0000 3. 7500 3. 5000 . 50000 . 25000 . 25000 . 26000 .1853 2 26

5 2 5. 0000 4. 7500 4. 5000 . 50000 . 25000 . 25000 . 26000 .1853 1 55 Table 75.

Recommended pitches, corresponding range of major diameters, and

basic thread data, American National Acme threads

Number of threads per inch, n

1.. m2..

2i/2 3..

4..

5.. 6-

8..

10.

12. 14.

16.

Recommended range of major diameters 1 Least

Inches

4. 5000

3. 5000

3. 0000

2. 2500

1. 7500

1. 5000

1. 1250 .8750

.7500 .5625

.4375 .3750

.3125

.2500

Greatest

Inches

13. 5000

10. 5000

9. 0000

6. 7500

5. 2500

4. 5000

3. 3750

2. 6250

2. 2500

1. 6875

1. 3125

1. 1250 .9375 .7500

Pitch, p

Inch

1. 00000

. 75000

. 66667

. 50000

. 40000

. 33333

. 25000

. 20000

. 16667

. 12500

. 10000

. 08333 .07143

.06250

Basic depth

of thread,

h = 0.5p

Inch

0. 5000 .3750

.3333

.2500 .2000

.1667

. 1250 .1000

.0833 .0625 .0500

.0417

.0357 .0312

Basic width

of flat, F=0.37069p

i These recommended least diameters correspond to a maximum helix angle (at the minor diameter) of approximately 5°. The recommended greatest diameters are 3 times the least.

5. CLASSIFICATION AND TOLERANCES

There is established herein for general use a single class of fit of American

National Acme screw threads.

(a) GENERAL SPECIFICATIONS

The following general specifications apply to all standard Acme screw threads:

1. Basic Diameters.—The maximum major and pitch diameters of the screw, and the minimum minor diameter of the nut are basic.

2. Tolerances.—(a) The tolerances specified represent the extreme variations allowed on the product.

(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.
164 NATIONAL SCKEW THREAD COMMISSION

(d) The tolerances on the thicknesses of threads are minus, and 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

and pitch are equal.

(J) The thread thickness tolerances include lead and angle errors.

(g) The tolerances on the major diameters of the screws and minor diameters

of the nuts are based upon the pitch of the thread.

(h) The minimum major diameter of the nut is at least 0.020 inch larger than

the basic major diameter. THREAD //V HUT

BASIC THICKNESS

M/N. r/Y/CXA/ttS OFOF THR^MB

M/N. T/-//C^A/£T-35 Of

7~/-//?£AD /A/ HUT

MAX. Trt/C/C,V£:5S QFj

T/i,9£AD ON SCREW

3 7O7p-.Q0S2r~-

FlGTJKE 54. -Illustration of allowances, tolerances, and crest clearances, Acme

threads. NOTATION p=pitch. /i=basic thread depth. Heavy line shows basic size.

(i) The maximum major diameter of the nut of a given pitch is such as to

result in a flat equal to 0.3707p — 0.0052 inch when the pitch diameter of the nut

is at its maximum value.

(j) The maximum minor diameter of a screw of a given pitch is such as to

result in a flat at the root equal to 0.3707^ — 0.0052 inch when the pitch diameter

of the screw is at its maximum value. 13

(b) LIMITING DIMENSIONS AND TOLERANCES

Limiting dimensions for standard Acme threads are given in table 76. The

application of these limits is illustrated in figures 54, 55, and 56.

1 3 When the width of flat of the cutting tool is at this maximum value the entire thread thickness or pitch diameter tolerance cannot be used without falling below the minimum limit on minor diameter of the screw.
AMERICAN" NATIONAL ACME SCREW THREADS 165

Figure 56.Illustration of tightest condition for 1%-inch 4 Acme threads.
NATIONAL SCREW THREAD COMMISSION

I

1

If"

B slim mil mil mi

I

on thickness of threads 3

§§§§§ sllil 11111 ssis

Pitch

diameter II

liill! Illli lilii 1111

SO T—It—< i-H i—IHi-1 MNW^

31 a Jlilli illli Ills

K C> H h'hhhh NNMii

1

1

SI

llllll illli Illli IHI

SO 1-irtHHH NNCO'*

Mini- mum

(basic) 3 llllll iiiii Illli 1111

SO i—I t—i i—1 i—i r-H NINCO^

1

s

1

1

ii

OS isllll Illli Illli Illl

11

00 llllll Hill illli mi

Tolerance equivalent on thickness of threads t~ Hill Hill Hill gggg

1

!

11

llllll IIIII Illli Illl

SO H HHHMH NCqri"*

Maxi- mum(basic) iiiiii urn mil mi

KO H HrirtHH NNW<*

Major

diameter ii

llllll Illli IIIII IIII

Maxi- mum

(basic) Inches 0.

2500

.3125 .3750

.

4375

.5000 .6250 .7500 .8750 1.

0000 1.

1250 1.

2500 1.

3750 1.

5000 1.7500 2.0000 2.5000 3.0000 4.0000 5.0000

Threads per

inch CM

Sm

1

:

!

i

i

i i i

i i !

Ii J

; :

;

;

i i

j

i

J i

; :

i

;

ii

i

Lh

i

;

J, j
AMEBICAIST NATIONAL ACME SCEEW THEEADS 167

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) GAGE TOLERANCES

Table 77 is given herein 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 of gages should be 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.

1. Tolerances on Lead.—The tolerances on lead given in table 77 are specified as an allowable variation between any two threads not farther apart than 12

inches.

2. Tolerances on Angle of Thread.—The tolerances on angle of thread, as

specified in table 77 for the various pitches, are tolerances on one half of the included angle. This insures that the bisector of the included angle will be per- pendicular to the axis of the thread within proper limits. The equivalent deviation from the true thread form caused by such irregularities as convex or con- cave sides of thread, or slight projections on the thread form, should not exceed

the tolerances permitted on angle of thread.

3. 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 77.

Tolerances for " go" and "not go" thread gages, American National

Acme threads

Threads per inch

Tolerance on thread

thickness at basic pitch line Tolerance

in lead

Tolerance on half angle of thread

Tolerance on major

diameter

Tolerance on minor

diameter From— To— From— To— From— To—

1 2 3 4 5 6 7 8 9

Inch Deg. Min.

In h Inch dz db Inch Inch Inch Inch

1 0. 0000 0. 0008 0. 0005 5 0. 0000 0. 0010 0. 0000 0. 0010 m .0000 .0007 .0005 5 .0000 .0010 .0000 .0010 1H - .0000 .0006 .0005 5 .0000 .0010 .0000 .0010

2. .0000 .0006 .0005 5 .0000 .0010 .0000 .0010

.0000 .0005 .0005 5 .0000 .0010 .0000 .0010

3 .0000 .0005 .0005 5 .0000 .0010 .0000 .0010

4 .0000 .0004 .0005 5 .0000 .0010 .0000 .0010

.0000 .0004 .0005 5 .0000 .0010 .0000 .0010

6 .0000 .0003 .0005 5 .0000 .0008 .0000 .0008 8 .0000 .0003 .0005 5 .0000 .0006 .0000 .0006

10 .0000 .0002 .0005 10 .0000 .0005 .0000 .0005

12 .0000 .0002 .0005 10 .0000 .0004 .0000 .0004

14 .0000 .0002 .0005 10 .0000 .0004 .0000 .0004

16 .0000 .0002 .0005 10 .0000 .0003 .0000 .0003

INDEX

A Page

Accuracy, control ol 143-152 Acme screw threads 161-167

historical -- 161 Allowance (definition) 8 (numerical values) 20, 28, 96, 157 American Gage Design Standards 51 American National: Acme general purpose thread series 163 coarse-thread series 14,32-37,42-45

8-pitch thread series - 68, 69, 71-72

fine-thread series 15, 38-41, 46-49

fire-hose coupling threads 94, 98 form of thread 11, 68, 76, 152 hose-coupling threads 92, 96 locknut threads 106-107 16-pitch thread series 68, 71, 75 standard hose connections 117-123

straight pipe threads. 104-108 taper pipe threads 101-103 threads for electric sockets and bases— 123-125

12-pitch thread series 68, 70, 73-74 Angle errors, diameter equivalent of 20, 22,24,28,96,128,157 Angle of helix (see Helix angle) 7 Angle of thread (definition) 7 Arrangement of report— 6 Authorization by Congress 2 Axis of screw (definition) 8

Base of thread (definition) 8 Basic size (definition) 8 Bolt and nut proportions 116 Bolts and nuts, screw threads for 11-67

carriage 116 machine. 116 plow 116 round unslotted head 116 step... 116 stove 116 tap.- 116 track 116 wrench head 116

Cable drilling tool joints 117 Cap screws 116 Carriage bolts 116 Chaser, thread 146 Chasers, died head 143, 146 Class 1, loose fit 19-20, 32, 38, 79 Class 2, free fit 20-22, 34, 39, 71-74, 79 Class 3, medium fit.. 22-26, 36, 40, 71-74, 79 Class 4, close fit 24-29, 37, 41, 79 Class 5, wrench fit for threaded studs 152-160

Classification of fits.. 16, 69, 77, 152 Clearance, crest 8

at major diameter 12, 162

at minor diameter 12, 152, 162 Close fit, class 4 24-29, 37, 41, 79 Comparators, thread 151 Core diameter (see Minor diameter) 7 Crest (definition) 7 Crest clearance (definition) 8 Cutter, thread milling 143,146 Cutting of screw threads 145-147 Cutting torch hose connections 117-123

Definitions Depth of engagement (definition), thread (definition)

7-8

182129—33- -12

Page

Diameter, major 7 minor 7 pitch 7 Die head chassers 143-146 Dimensions (tables of thread) . .. 14-15, 31-49, 69-75,

&3-90, 92, 94, 96-97, 102-103, 105, 107, 124-125,

144, 157-159, 163, 166. Directions of tolerances on—

gages 53,56-58,76 hose couplings 94 pipe threads 104 screw and nut 17, 78 E

Electric socket threads 123-125 Engagement, depth of 8 length of 8,16,19,72-76,104

Errors, control of lead 28, 144-145 Error, diameter equivalents of lead and angle. 20,

22, 24, 28, 96, 128, 157 European trip 4,6 External thread (definition) 7 F

Fillets in Acme threads 162 Finish (definition) 8

Fit, close, class 4. _ 24-29, 37, 41, 79

(definition) 8

free, class 2 20-22, 34, 39, 71-74, 79

loose, class 1 19-20, 32, 38, 79 medium, class 3_ 22-26, 36, 40, 71-74, 79 wrench, class 5 152-160

Fits, common practice 161 Form of Acme threads 161 American National coarse and fine threads - 11 fire-hose coupling threads 92 hose-coupling threads 92 pipe threads 100 threads of special diameters and

pitches... 68,76 Free fit, class 2 20-22, 34, 39, 71-74, 79 G

Gage classification 51, 110 design standards 51 practice recommended 55, 111 thickness . 152 Gages, American standard 51 American National Acme screw threads.. 167 American National coarse and fine threads 50-67 American National fire-hose coupling

threads 98-99 American National pipe threads 109-115 checking plug ..51,110

class W 53,58,76

class X 52,56,76

class Y 53,57,76

class Z 53, 57, 76

classification as to accuracy 52 dimensions of 59-67, 99, 114, 118-123

direction of tolerances on 53, 56-58, 76

electric socket 125

" go" and "not go" 50, 150-152 hose connection 98, 118-123 indicating 151 inspection 52,98,110,125 lamp base. 125 marking of 10,56,82 master 52 measurement of 56, 129-142, 152 mechanical 51 optical 51,151 169
170 INDEX

Page

Gages, plain 54,152

setting 52

specifications for 52,109

testing of 152 thread plug 53, 151 thread ring 53, 151 thread snap 150 threads of special diameters and pitches.. 82

tolerances on 55-58, 76, 113, 125, 167 wear on 53 working 52, 111 wrench fit 160 Gaging 50-52

98, 111-112, 118-123, 125, 150-152, 160, 167 fundamentals of 50,109,167

object of 50 practices 111, 150-152, 160 Grinding threads 149 H

Hearings, public 5 Helix angle (definition) 7 Historical 1, 91, 99, 116, 117, 161 Hob, threading 147 Hobs, tooth outlines of 143, 147 Hose-connection gages 98, 118-123 Hose connections for torches 117-123 Hose threads 91-99

Interchangeability 2 Internal thread (definition) 7 International standardization 6 L

Lamp-base threads 123-125 Lapping of screw threads 150 Lead (definition) 7

errors, control of 144 diameter equivalent of.. 20, 22, 24, 28, 96, 128, 157 Lead screw 144 Length of engagement (definition) 8 pipe thread 104 Lengths, bolt and screw 116 tolerances on . 116 Limits (definition) 8 Line pipe 117 Locknut threads 106 Long screw j oints 105 Loose fit, class 1 19-20, 32, 38, 79 M

Machine bolts 116 Machine-screw nuts 116 proportions 116 Major diameter (definition) 7 Manual on pipe threads 99, 109 Marking of gages 10, 56, 82

tools 10 Measurement of pitch diameter 129-137 thread gages 56, 129-142, 152 thread thickness 138-142 wire methods of 129-142 Measuring pressure. 52, 131 Medium fit, class 3 22-26, 36, 40, 71-74, 79 Members of commission 3 Micrometers, thread 150 Minor diameter (definition) 7 uniform, of nut... 16,163 N

Net tolerances, basis of 127 Neutral zone (definition) 8 Nomenclature (see Terminology) 7 Notation 9-12, 95, 100-101, 105-106, 162 Number of threads (definition) 8 Nut 7 proportions 116 O

Oil-well casing threads 117

drilling equipment 117 Organization of commission 3-6 Outside diameter (see Major diameter) 7

Page

Pipe dimensions, tables of 107-109

specifications.. 107-109,117 thread gages 109-115 manual 99, 109 threads, straight 104 taper 101 Pitch (definition) 7 diameter (definition) 7 measurement of 129-137 uniform, of minimum nut 16, 77, 153 Plow bolts 116-117 Practice for fits and thread series 161 Pressure, measuring 52, 131 Procedure of commission 5 Proportions, screw, bolt, and nut 116 Public hearings. 5 R

Report, arrangement of 6 Rethreading tools 91 Riverts, tap.. 116 Roll, threading 148 Roller dies 148 Rolling of screw threads 147 Root (definition) 7 Rotary drilling taper joints 117 S

Screw 7

axis 8 lengths 116 proportions 116-117 thread (definition) 7 threads, American National Acme 161-167 cutting of 145-147

finishing of 149

for oil-drilling equipment 117 hose-coupling 91-99 miscellaneous special 76-90, 117-125 regular (see American National)

.

rolling; of 147 special 76-90

tools for cutting 145-147 Screws, cap 116 hexagon head... 116 machine 116

set -~ 116 wood 116 Set screws 116 Side of thread (definition) 8 Standard temperature 52 Stove bolt nuts 116 proportions 116 Straight pipe threads 104 Sucker rod specifications 117 Symbols 9-11, 101 T

Tap bolts —- 116

rivets 116 Taper, effect on thread depth 100 threads, measurement of 133-135 Taps - 143,146 marking of 10 Temperature, standard 52 Terminology 7-11 Thread (see Screw threads). angle -- 7 depth 8

series (see American National)

.

common practice 161 Threads, internal and external 7 Tolerance (definition).. 8 pitch diameter 17, 78, 94, 104, 128 Tolerances: Acme thread 163-164 derivation of _ 127-129 direction on gages 53, 56-58, 76 gage . 55-58, 76, 113, 125, 167 hose couplings 94-96
INDEX 171

Tolerances— Continued Page

numerical values:

class 1, loose fit 20,84

class 2, free fit 22, 71-74, 86

class 3, medium fit 24, 71-75, 88

class 4, close fit 28,90

class 5, wrench fit 157 on length of screws, etc 116 pipe threads 104 (product specifications) 16-31, 69-75, 77-90, 94-96, 101-107, 152-154, 163-166 screw and nut 16-19 wood screws- 116 wrench openings .. 116 Tool, single point 145 Tools:form of 143 marking of 10 rethreading for fire-hose threads 91 tooth outlines 143

Page

Torques, wrench fit, for studs 158-159 U

Uniform minimum nut 16, 77, 153 Utility of report . . 6 W

Welding torch hose connections 117-123 Wire methods of measurement 129-142 Wires, measurement of 131

sizes of 129

specifications for 130 Wood screws 116 Working-barrels 117 Wrench fit, class 5, for threaded studs 152-160 Wrench head bolts. 116 Wrench openings.. „ 116 O