DEPARTMENT OF COMMERCE

BUREAU OF STANDARDS

S. W. STSATTON, Duticrot

PROGRESS REPORT

OF THE

NATIONAL SCREW THREAD COMMISSION

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

AS APPROVED JUNE 19, 1920

JANUARY 4, 1921

MISCELLANEOUS PUBLICATIONS

OF THE

BUREAU OF STANDARDS

No. 42

WASHINGTON «OVIRNMENT PRINTING OFFICE
. -

-
NATIONAL SCREW THREAD COMMISSION,

WASHINGTON,

June ig, 1920.

The accompanying Progress Report of the National Screw

Thread Commission has been approved by the Commission, and

by the Secretaries of War, Navy, and Commerce, in accordance

with the provisions of the law establishing the Commission.

APPROVAL BY THE MEMBERS OF THE COMMISSION.

The Progress Report of the National Screw Thread Commission, as

revised in accordance with the vote of November 23-24, 1919, and

embodying certain changes recommended by a special committee of the Society of Automotive Engineers, is hereby approved.

S. W. Stratton,

Chairman.

B. C. Peck,

J. O. Johnson,

Representing the United States Army.

N. H. Wright,

P. M. McNair,

Representing the United States Navy.

James Hart'ness,

F. O. Wells,

Nominated by the American Society of Mechanical Engineers. E. H. Ehrman,

H. T. Herr,

Nominated by the Society of Automotive Engineers.

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

doc. No. 201, 65th Cong., H. R. 10852), is hereby accepted and approved.

Newton D. Baker,

Secretary of War.

Josephus Daniels,

Secretary of the Navy.

Joshua W. Alexander,

Secretary of Commerce.

35455°—21

WASHINGTON : GOVERNMENT PRINTING OFFICE : 1921

DEPARTMENT OF COMMERCE

BUREAU OF STANDARDS

S. W. STRATTON, Director

PROGRESS REPORT

OF THE

NATIONAL SCREW THREAD COMMISSION

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

AS APPROVED JUNE 19, 1920

JANUARY 4, 1921

MISCELLANEOUS PUBLICATIONS

OF THE

BUREAU OF STANDARDS

No. 42

WASHINGTON GOVERNMENT PRINTING OFFICE

1921
PREFACE

Recognizing the impossibility of bringing out a report of this

character which in the first issue in entirely free from error or

inconsistency, Congress has extended the life of the commission

for a period of two years, in which such corrections and changes

will be made as are found necessary or desirable by practical use of

the report in the designing room and in the shop.

Criticisms and suggestions for the improvement of the report

should be addressed to the National Screw Thread Commission,

Bureau of Standards, Washington, D. C.

2
PROGRESS REPORT OF THE NATIONAL SCREW

THREAD COMMISSION

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

AS APPROVED JUNE 19, 1920

CONTENTS Page Preface 2

I. Introduction 4

1 . Origin and progress of commission 4

2. Purpose of report , . 4

3. Utility of report 5

4. Organization and procedure of commission 5

5. Arrangement of report 5

II. Terminology 6

1. Introductory 6

2. Definitions 6

3. Symbols 8

4. Illustrations showing terminology 9

III. Form of thread 9

r. National form 9

2. National fire-hose coupling-thread form 13

3. National hose-coupling thread form 16 IV. Thread series adopted 16

1. Introductory : 16

2. National coarse-thread series 17

3. National fine-thread series 17

4. National fire-hose coupling threads 18

5. National hose-coupling threads 18

6. National pipe-thread series 19 V. Classification and tolerances 21

1. General L 21

2. Classification of fits 22

(a) General specifications 23

(b) Class I, loose fit 23

(c) Class II-A, medium fit (regular) 33

(d) Class II-B, medium fit (special) 41

(e) Class III, close fit -. 47

(/) Class IV, wrench fit 55

3. Tolerances 56

(a) Tolerances represent extreme variations 56

(6) Pitch diameter tolerances 56

(c) Class I and Class II tolerances. . v 56

(d) Pitch diameter tolerances on screw 56

(e) Tolerances on major diameter of screw 56

(J) Tolerances on minor diameter of screw 56

(g) Tolerances on major diameter of nut 57

(h) Tolerances on minor diameter of nut 57

(i) Illustration 57

(_/') Scope of tolerance specifications 57

3
4 NATIONAL SCREW THREAD COMMISSION

Page VI. Gages S 8

i. Introductory 58

(a) Fundamentals 58

(b) Gage classification 60 VII. National pipe threads 60

1. Introductory 60

2 . National standard pipe threads 61 VIII. Future work of commission 84 Threads requiring standardization 84

2. Standardization of products closely allied to the manufacture of screw threads 84

3. Possibility of international standardization 84 IX. Appendixes 86

1. Origin of the commission 86

2. Organization of the commission 87

3. Procedure of commission 89

4. Historical 93

5. Technical 94

6. Gages and methods of test 98

7. Typical specifications for screw-thread products 107 X. Index 109

I. INTRODUCTION

1. ORIGIN AND PROGRESS OF COMMISSION

The National Screw Thread Commission, which was created by

an act of Congress (H. R. 10852) approved July 18, 191 8, for the

purpose ofv ascertaining and establishing standards for screw

threads for use of the various branches of the Federal Government and for the use of manufacturers, recommends herewith

certain systems of threads, together with information, data, and

specifications pertaining to the manufacture of the threads recom- mended.

2. PURPOSE OF REPORT

It is the desire of the commission to make available to American manufacturers at the present time the information contained

in its progress report for immediate use, rather than delay making

a report in order to consider more fully the possibilities of international standardization of screw threads. It is the opinion of

the commission, however, that international standardization of screw threads is very desirable and that the present time is most

opportune for accomplishments in this direction. Further refer- ence is made to the possibilities of international standardization

in Section VIII of this report.

In the time provided in the act of Congress the commission

has devoted its attention to the standardization of only those

threads, sizes, types, and systems which are of paramount importance by reason of their extensive use and utility. As indi-
PROGRESS REPORT 5

cated in Section VIII, there remains much to be accomplished

along the lines of standardization of special but important threads,

and of maintaining progress in our standardization work in keeping with the developments of manufacturing conditions.

3. UTILITY OF REPORT

The advances made by the commission up to date will reduce

the variety of screw threads in general use, 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, and

aeroplane, and in general will increase the dependability of all mechanisms. The war has given a new life to industrial activities

in all countries and has made it necessary for us not only to share

in the progress in standardization but to take advantage of every

possible means to maintain America's progress. We, as a people,

are keenly awake to the economic necessities of the reconstruction

period and the period of peace following, and every step toward

standardization of our products will result in increased production

with a minimum expenditure of materials, energies, and other

resources.

4. ORGANIZATION AND PROCEDURE OF COMMISSION

Prior to the formal appointment, under date of September 21,

1 918, of the various commissioners, a preliminary meeting was

held at "Washington, D. C, on September 12. At this preliminary

meeting was outlined the detailed organization of the commission

as described in Appendix 2 and, also, a program covering the procedure of the commission as described in Appendix 3. The commission in formulating this progress report has acted

largely in the capacity of a judiciary, 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 matters of particular importance and of general interest, while in the appendixes

there is arranged detailed information of both a general and a

technical nature. There is included in the body of the report
6 NATIONAL SCREW THREAD COMMISSION

sufficient information to permit the writing of definite and complete specifications for the purchase of screw-thread products,

and there is included in the appendixes material which explains

or goes more fully into the application of the specifications. The

subjects covered in the report are arranged in the following

manner

I. Introductory.

II. Terminology.

III. Form of thread. IV. Thread series adopted. V. Classification and tolerances. VI. Gages. VII. National pipe threads. VIII. Future work of commission. IX. Appendixes. X. Index.

II. TERMINOLOGY

1. INTRODUCTORY

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

nontechnical words and terms which would best convey to the

producer and user of screw threads the information presented.

2. DEFINITIONS

The following definitions are given of the more important

terms used in the report. Definitions of terms which are obviously elementary in character are intentionally omitted.

(a) Words Relating to Screw Threads.—i . Screw Thread.—

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

inside or outside surface of a cylinder or cone.

2. Screw Helix.—The path of a point moving at a uniform

angular rate on a cylindrical or conical surface and at the same

time moving at a uniform axial rate.

3. Major Diameter {formerly known as "outside diameter")

—

The largest diameter of the thread on the screw or nut. The term

"major diameter" replaces the term "outside diameter" as applied to the thread of a screw and also the term "full diameter"

as applied to the thread of a nut.

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

smallest diameter of the thread on 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 which would pass through the threads at
PROGRESS REPORT 7

such points as to make the width of the threads and the width

of the spaces cut by the surface of the cylinder equal

6. Pitch.—The distance from a point on a screw thread to a

corresponding point on the next thread measured parallel to the

axis.

p Number of threads per inch.

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

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

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

the thread measured in an axial plane.

9. Helix Angle.—The angle made by the helix of the thread at the pitch diameter with a plane perpendicular to the axis.

10. Crest.—The top surface joining the two sides of a thread.

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

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

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

screw.

14. Base of Thread.—The bottom section of the thread, the

greatest section between the two adjacent roots.

15. Depth of Thread.—The distance between the top and the

base of thread measured normal to the axis. 16. Number of Threads.—Number of threads in any unit of

length.

17. Length of Engagement.—The length of contact between

two mating parts, measured axially.

18. Depth of Engagement.—The depth of thread in contact of

two mating parts, measured radially.

(6) Words Relating to Classification and Tolerances.—

1. Allowance {Neutral Zone).—A difference in dimensions, the

limits of which are prescribed; it is to provide for different kinds

or classes of fit. 2. Tolerance.—A definite difference in the dimensions prescribed in order to permit of variations in manufacture.

Extreme Tolerance.—The maximum and minimum tolerance

permitted by the designer, the limits of which are to be placed on the drawings. It is the net tolerance as affected by the

master-gage tolerance.
8 NATIONAL SCREW THREAD COMMISSION

Net Tolerance.—The tolerance limits within which the product

is ordinarily passed by the master gages. It is the extreme

tolerance as affected by the master-gage increment.

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

all variations are made.

4. Finish.—The character of the surface on a screw thread.

5. Crest Clearance.—Defined on a screw form as the space

between the top of a thread and the root of its mating thread.

6. Fit.—The relation between two mating parts with reference

to ease of assembly; for example: Wrench fit; close fit; medium

fit; loose fit. The quality of fit is dependent upon both the

relative size and the quality of finish of the mating parts.

7. Neutral Zone {Allowance).—A space between the mating

parts which must not be encroached upon.

8. Gage Increment.—Gage increment is a predetermined allow- ance by which the net tolerance of the product is increased for

gaging purposes.

9. Limits.—The extreme dimensions, which are prescribed, to

provide for variations in fit and workmanship.

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 P =jr

Pitch or thread interval b =— ^ n

Helix angle s p Tangent of helix angle S =

3.14159X.E Width of basic flat at top, crest, or root F

Depth of basic truncation /

Depth of sharp V-thread H

Depth of national (U. S.) form of thread h Included angle of taper Y

(One-half included angle of taper) y Additional Symbols for national pipe threads are given in Sec. VII.
PROGRESS REPORT 9

Symbols are for use on correspondence, drawings, shop and

storeroom cards, specifications for parts, taps, dies, gages, etc., and on tools and gages.

The basis of the system is the initial letters of the series, preceded by the diameter in inches (or the screw number) and number

of threads per inch, all in Arabic characters, followed by the classi- fication of fit in Roman numerals. Examples:

National Coarse-Thread System: To specify a threaded part i in. -diameter, 8 threads per inch, Mark

Class I fit x"—8

NC—

I

National Fine-Thread System:

Threaded part i in. -diameter, 14 threads per inch, Class III fit. x"—14

NF—III National Form, Special Pitch: Threaded part 1 in. -diameter, 12 threads per inch, Class IV fit. x"—12

N—IV

National Pipe-Thread Series: National taper pipe thread. Threaded part 1 in.-diameter,

1 x% threads per inch 1"—1 i^—NPT

National straight pipe thread x"—xx%—NPS

National Fire-Hose Thread Series and National Hose-Thread

Series: Threaded part 3 in.-diameter, 6 threads per inch 3"—6

NH

Threaded part 1 in.-diameter, 11% threads per inch x"—

NH

Remarks.—The number of threads per inch must be indicated

in all cases, irrespective of whether it is the standard number of

threads for that particular size of threaded part or special.

Symbols for Wire Measurements

Measurement over wires Diameter of wire

(Corresponding radius).

.

1. NATIONAL FORM

M

G

9

4. illustrations showing terminology

The following illustrations of thread forms illustrate the use of

the terms used in the report and as previously defined. (See

Figs. 1 and 2.)

III. FORM OF THREAD

The national form of thread profile as specified herein, and

known previously as the United States Standard or Sellers' Profile, is adopted by the commission and shall hereafter be known

as the National Form of Thread.

(a) Where Used.—The National Form of Thread Profile shall

be used for all screw-thread work except when otherwise specified

for special purposes.
IO NATIONAL SCREW THREAD COMMISSION

(b) Specifications.—The basic angle of thread (A) between

the sides of the tliread measured in an axial plane shall be 6o°.

The line bisecting this 6o° angle shall be perpendicular to the axis

of the screw thread.

-MAJOR DJAM. -PJTCH D/ftfyir

SCREW.

(Outside Dia.]B

\ (EffectiveDia)E

(Core DicQ K

HELIXANGLEftJ

-PITCH

i

Fig. i. —Screw thread notation The basic flat at the root and crest of the thread form will be

yi Xp, or 0.125X/).

The basic depth of the thread form will be 0.649519 X p =

0649519 n

where p = pitch in inches, n = number of threads per inch.
PROGRESS REPORT II

(c) Illustration.—There are indicated in Fig. 3 the relations as

specified herein for the National Form of Thread for the minimum

nut and maximum screw, medium fit. These relations are further

shown in Figs. 5, 9, and 11.

(d) Clearance in Nut.—1. Clearance at Minor Diameter.—

A

clearance shall be provided at the minor diameter of the nut by

Fig. 2.Screw thread notation removing the thread form at the crest by an amount equal to onesixth to one-fourth of the basic thread depth.

2. Clearance at Major Diameter.—A clearance at the major

diameter of the nut shall be provided by decreasing the depth of

the truncation triangle by an amount equal to one-third to twothirds of its theoretical value.
12 NATIONAL, SCREW THREAD COMMISSION

National form of thread for minimum nut and maximum

screw

Note.—No allowance is shown. This condition exists in Class II, Medium Fit, where both the minimum nut and the maximum screw are basic. NOTATION

A=bO° Angle of thread

a=30° One-half angle of thread

p=- Pitch n n=

H=0.866025 p

h- .649519 p

5/6/i= .541266/?

F= .125000 p

f= .108253 p = l/8H =l/6/i

Fig. 3.

Nationalform of thread

. . Number of threads per inch

. .Depth of 60° sharp V thread

. . Depth of national form thread

. . Width of flat at crest and root of national

form

Depth of truncation
PROGRESS REPORT 13

2. NATIONAL FIRE-HOSE COUPLING THREAD FORM

For threads cut on fire-hose couplings the form of the thread

profile will be as specified herein and previously known and specified as the National Standard Hose Coupling Thread recommended

(See Tables 3 and 4 for dimensions. See Table 5 for tolerances)

Fig. 4.National fire hose and national hose coupling threads by the National Fire Protection Association and by the Bureau of

Standards, and known hereafter as the National Fire-Hose

Coupling Thread.

(a) Specifications.—The basic angle (A) between the sides of

the thread measured in an axial plane shall be 6o°. The line

bisecting this 6o° angle shall be perpendicular to the axis of the screw thread.
NATIONAL SCREW THREAD COMMISSION

Allc>*rc>r>cGsi and <Z>Jear<ar>ces Of

7s threads per Inch

BASIC ^/ZSsS

Fig. 5.National fire hose coupling thread
PROGRESS REPORT 15

National hose couplings tolerances, allowances, and clearances, illustrated for 3/4 in. —11 1/2 threads per inch

COUFUNGFORM

—/V O T*\ TV O /V—

p = ri+ch

h = Basic. 7~hr&adDepth

= o. e,** &&/9p

f = Sa&tc. Oe/o^h of

yraneicrf-ior-i

Fig. 6.

National hose coupling thread
i6 NATIONAL SCREW THREAD COMMISSION

The crest and root of the basic thread form will be flattened or truncated from a sharp V-form as follows:

Threads per inch. '. Depth of truncation in inches 4 o. 02

6 01 7K 01

3. NATIONAL HOSE-COUPLING THREAD FORM

For threads cut on hose couplings from |^ inch to 2 inches, inclusive, the National Form of Thread shall be used as specified under

Section III, "Form of Thread."

IV. THREAD SERIES ADOPTED

1. INTRODUCTORY

It is the aim of the commission, in establishing thread systems

for adoption and 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 present "United States Standard" threads, supplemented in

the sizes below one-fourth inch by the standard established by the

American Society of Mechanical Engineers (A. S. M. E.). The

fine-thread series is composed chiefly 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.)

The recommendation of these standards will tend toward their

more universal use, and will constitute important gain that is affected by standardization with a minimum handicap.

Also, the testimony was very consistent in favoring the adoption in practically its present shape of the American Briggs

standard pipe-thread sizes as recommended by the American

Society of Mechanical Engineers and the fire-hose coupling sizes as

established by the National Fire Protection Association.
PROGRESS REPORT 17

2. NATIONAL COARSE-THREAD SERIES

There is specified in Table 1 a thread series which will be known

as the National Coarse-Thread Series. This series contains certain

sizes known previously as the United States Standard threads

and also certain sizes known as the A. S. M. E. machine-screw

threads. There are included in the National Coarse-Thread

Series only those sizes which are essential.

(a) WHERE Used.—The National Coarse Threads are recom- mended 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.

(&) Specifications.—The series of sizes and basic dimensions

are specified in Table 1

.

1 . Form of Thread.—The standard form of thread profile shall be

used as specified and described in Section III, "Form of Thread."

2. Classification and Tolerances.—The National Coarse Thread

shall be manufactured in accordance with the specifications as given in Section V, "Classification and Tolerances."

3. Gages.—The gages used for the manufacture of National

Coarse Threads will be as specified in Section VI, "Gages."

3. NATIONAL FINE-THREAD SERIES

The threads specified in Table 2 will be known as the National

Fine-Thread Series. This series contains certain sizes known

previously as the S. A. E. threads, and, also, certain sizes known

as the A. S. M. E. machine-screw sizes. There are included in the

National Fine-Thread Series, only the sizes which are essential.

(a) Where Used.—The National Fine Threads are 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, such as, for instance, on large sizes where sufficient force can not be secured to set properly a screw or bolt of coarse pitch, by exerting on an ordinary

wrench the strength of a man.

(b) Specifications.—The series of sizes and basic dimensions

are specified in Table 2.

j. Form of Thread.—The standard form of thread profile shall

be used as specified and described in Section III, "Form of

Thread."

12071°—21 2
1 8 NATIONAL SCREW THREAD COMMISSION

2. Classification and Tolerances.—The National Fine Thread

shall be manufactured in accordance with specifications given in

Section V, "Classification and Tolerances."

3. Gages.—The gages used for the manufacture of National

Fine Threads will be as specified in Section VI, "Gages."

4. NATIONAL FIRE-HOSE COUPLING THREADS

There is specified in Table 3 a thread series and basic dimensions

for fire-hose couplings from 2}4 to \Y2 in. diameter which will

be known as the 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.

(a) Where Used.—The National Hose Thread shall be used 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 23^ and 4^ in. in diameter.

(b) Specifications.—Series of sizes and basic dimensions for

National Fire-Hose Threads are specified in Table 3.

1. Form of Thread.—There should be used a special form of

thread as specified for National Fire-Hose Threads in Section III,

"Form of Thread."

2. Classification and Tolerances.—National Fire-Hose Threads

shall be manufactured in accordance with the specifications as given in Section V, "Classification and Tolerances."

3. Gages.—The gages used for the manufacture of National

Fire-Hose Threads will be as specified in Section VI, "Gages."

5. NATIONAL HOSE-COUPLING THREADS

There is specified in Table 4 a thread series and basic dimensions for hose-coupling threads from ^ to 2 in. in diameter,

which will be known as the National Hose-Coupling Threads.

(a) Where Used.—The National Hose-Coupling Thread shall

be used on all couplings and connections where sizes between

and 2 in. in diameter are required.

(b) Specifications.—The series of sizes and basic dimensions

for National Hose-Coupling Threads are specified in Table 4.

1. Form of Thread.—The National Form of Thread as specified

in Section III, "Form of Thread," should be used.

2. Classification and Tolerances.—The National Hose-Coupling

Thread shall be manufactured in accordance with the specifications as given in Section V, "Classification and Tolerances."
PROGRESS REPORT 19

3. Gages.—The gages used for the manufacture of the National

Hose-Coupling Thread will be as specified in Section VI, "Gages."

• 6. NATIONAL PIPE-THREAD SERIES

There are specified in Section VII, Tables 19, 20, and 21, thread

series and basic dimensions for National Taper Pipe Threads,

National Straight Pipe Threads, and National Locknut Threads.

TABLE 1.—National Coarse-Thread Series

Identification Basic diameters Thread data

1 2 3 4 5 6 7 8

n D E K Metric p h

Sizes equivalent Threads Major Pitch Minor of major Pitch Depth ot per inch

-

diam. diam. diam. diam. thread

T U lliLii d b Inch Inch

64 073 0629 0527 1 854 n n 1 c-fi?^ U. Ul OO-OU 0101

2 56 .086 .0744 .0628 2.' 184 . 0178571 .0116

3 48 .099 .0855 .0719 2.515 . 0208333 .0135

4 40 .112 .0958 .0795 2.845 .0250000 .0162

5 40 .125 .1088 .0925 3.175 .0250000 .0162

6 32 .138 .1177 .0974 3.505 . 0312500 .0203

8 32 .164 .1437 .1234 4.166 . 0312500 .0203

10 24 .190 .1629 .1359 4.826 .0416667 .0271

12 24 .216 .1889 .1619 5.486 .0416667 .0271 M 20 .2500 .2175 .1850 6.350 . 0500000 .0325

•fV 18 .3125 .2764 .2403 7.938 .0555556 .0361 Vs 16 .3750 .3344 .2938 9.525 .0625000 .0406 A 14 .4375 .3911 .3447 11.113 .0714286 .0464

V* 13 .5000 .4500 .4001 12.700 .0769231 .0500 h 12 .5625 .5084 .4542 14. 288 .0833333 .0541 % 11 .6250 .5660 .5069 15. 875 . 0909091 .0590 % 10 .7500 .6850 .6201 19. 050 . 1000000 .0650

9 .8750 .8028 .7307 22. 225 .1111111 .0722

1 8 1.0000 .9188 .8376 25.400 . 1250000 .0812

7 1.1250 1.0322 .9394 28. 575 . 1428571 .0928

7 1 2500 1.1572 1.0644 31.750 . 1428571 .0928 6 1.5000 1.3917 1.2835 38. 100 . 1666667 .1083

5 1.7500 1.6201 1.4902 44.450 . 2000000 .1299

2 4^ 2.0000 1.8557 1.7113 50. 800 .2222222 .1443 2H 4^ 2. 2500 2. 1057 1.9613 57. 150 .2222222 .1443

2V2 4 2. 5000 2.3376 2. 1752 63.500 .2500000 .1624 2M 4 2.7500 2.5876 2.4252 69.850 .2500000 .1624

3 4 3.0000 2.8376 2.6752 76. 200 .2500000 .1624
20 NATIONAL SCREW THREAD COMMISSION

TABLE 2.—National Fine-Thread Series

Identification Basic diameters Thread data

1 2 3 4 5 6 7 8

n D E E Metric V ?! Sizes equivalent Threads Major Pitch Minor of major Pitch jjeptn ot per inch diam. diam. diam. diam. thread

Tn rTi PC Incti 6 S Inches mm Inch Inch 1° 0.060 0.0519 0. 0438 1.524 0.0125000 0.00812

1 V2 .073 .0640 .0550 1.854 .0138889 . 00902

2" 64 . 086 . 0759 . 0657 2. 184 . 0156250 .01014

3 56 . 099 . 0874 . 0758 2. 515 . 0178571 . 01160

4 48 . 112 . 0985 . 0849 2.845 . 0208333 . 01353

5 44 .125 .1102 .0955 3.175 .0227273 .01476

6 40 .138 .1218 .1055 3. 506 .0250000 .01624

8 36 . 164 . 1460 . 1279 4. 166 . 0277778 . 01804

10

" 32 . 190 . 1697 . 1494 4. 826 .0312500 . 02030 12 28 . 216 . 1928 . 1696 5. 486 . 0357143 . 02319 M 28 .2500 .2268 .2036 6.350 . 0357143 . 02319 A 24 .3125 .2854 .2584 7.938 . 0416667 . 02706

24 . 3750 . 3479 . 3209 9. 525 . 0416667 . 02706 £ 20 . 4375 . 4050 . 3725 11. 113 . 0500000 . 03248 72 20 . 5000 . 4675 . 4350 12. 700 . 03248

18 .5625 .5264 .4903 14.288 .0555556 .03608

13 .6250 .5889 .5528 15.875 .0555556 . 03608 & 16 .7500 .7094 .6688 19. 050 .0625000 .04060 % 14 .8750 .8286 .7822 22.225 .0714286 . 04640

l 14 1.0000 .9536 .9072 25.400 .0714286 . 04640

12 1.1250 1.0709 1.0167 28. 575 . 0833333 . 05413

12 1.2500 1.1959 1.1417 31.750 .0833333 .05413

12 1.5000 1.4459 1.3917 38. 100 .0833333 . 05413 1M 12 1.7500 1.6959 1.6417 44.450 .0833333 . 05413

12 2.0000 1.9459 1.8917 50. 800 .0833333 .05413

2}4 12 2. 2500 2.1959 2.1417 57.150 . 0833333 .05413

12 2.5000 2.4459 2.3917 63. 500 . 0833333 . 05413 2% 12 2.7500 - 2.6959 2.6417 69. 850 . 0833333 .05413

3 10 3. 0000 2.9350 2.8701 76. 200 . 1000000 . 06495

TABLE 3.—National Fire-Hose Couplings BASIC MINIMUM COUPLING DIMENSIONS

Nominal

size

Threads

per inchPitch in inches

Depth of thread

in inches

Major dia. mmmeter in

Inches

Pitch diameter

in inches

Minor

diameter

in

inches

Allowance, inches

2.5000

3. 0000 3.5000

4. 5000

7.5

6.0

6.0

4.0

0. 13333

. 16667

. 16667 .25000

0. 0955

.1243 .1243

.1765

78. 550

92. 837

108. 712 147.320

3.0925 3.6550 4.2800

5. 8000

2.9970

3. 5306

4. 1556

5. 6235

2.9015

3.4063

4.0313

5. 4470

0.03

.03

.03

.05

BASIC MAXIMUM NIPPLE DIMENSIONS

2.5000

3. 0000

3. 5000

4. 5000

7.5 6.0 6.0

4.0

0. 13333

. 16667

. 16667 .25000

0.0955

.1243

.1243

.1765

77.788 92.075

107. 950

146. 050

3. 0625

3. 6250

4. 2500

5. 7500

2. 9670

3. 5006

4. 1256 5.5735

2.8715

3. 3763 4.0013

5. 3970

0.03

.03

.03

.05
PROGRESS REPORT 21

TABLE 4.—National Hose-Coupling Threads

BASIC MINIMUM COUPLING DIMENSIONS

Nominal

size

Threads

per

inch

Pitch in inches

Depth of thread

in inches

Major diameter in

Pitch diameter

in inches

Minor

diameter

in inches

Allowance, inches mm Inches

%

1

2

ny2 ny2 ny2 ny2 \\v%

0. 08696

.08696

. 08696

. 08696

. 08696

0. 0565

.0565 .0565

.0565 .0565

27.242

33. 150

41. 908 47.976

60.015

1.-0725

1. 3051 1.6499

1.8888 2.3628

1.0160

1.2486

1.5934

1.8323

2.3063

0.9595

1. 1922

1. 5369

1. 7759 2.2498

0.01

.01

.01 .01

.01

BASIC MAXIMUM NIPPLE DIMENSIONS

H

lm

V4

2

ny2 ny2 ny2 uy2

0. 08696

.08696

. 08696

. 08696

. 08696

0.0565

. 0565

.0565

.0565

.0565

26. 988

32. 896

41. 654

47. 722

59. 761

1.0625

1.2951

1.6399 1.8788 2.3528

1. 0060

1.2386

1. 5834

1.8223 2.2963

0.9495

1.1822

1.5269

1.7659 2.2398

0.01

.01

.01

.01 .01

V. CLASSIFICATION AND TOLERANCES

1. GENERAL

One of the most important phases of standardization of screw- thread products is that of interchangeability. The direct result

of establishing a national thread system will be the elimination of

many unnecessary sizes. Of even more importance are the advantages to be gained in the manufacture of interchangeable screw- thread parts, which having been made in different manufacturing

plants at widely separated points, will assemble without difficulty

and in a manner which will insure proper operation of the mechanism being produced.

(a) Strict Interchangeability.—Many manufacturers, previous to the war, were making interchangeable machine parts in

their own shops where there was but one master gage or reference

standard, but one individual who had authority to pass on parts

in dispute, and where it was possible to secure assembly and satisfactory operation by fitting the parts.

The experience gained by manufacturers producing war material has demonstrated the economic advantage of producing interchangeable parts, especially where large quantities of parts are manufactured. In addition to the direct saving in the cost of

manufacture, the numerous other advantages to be gained will

make it mandatory that the procedure for producing interchange-
22 NATIONAL SCREW THREAD COMMISSION

able work as specified under the subject of classification and toler- ances be explicitly followed, if we are to keep pace or lead in the

world's progress as manufacturers.

(6) Need of Definite Specifications.—The difficulties en- countered in obtaining enormous quantities of war material needed

by the United States Government during the recent World War

has pointed out to Government authorities, as well as manufacturers, the need of writing definite and complete specifications for

material required. All specifications should be so written that

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

known measurable standards and correctly defined by the largest

tolerance limits compatible with the satisfactory operation or performance of the articles or material for the purpose intended. To

this end every factor involved in the acceptability of the manufactured product required should be comparable within specified

limits with a known measurable standard. Every specification

should be so concise that no dispute regarding the limiting lines

of acceptance can arise.

The specifications stated under classification and tolerances

are intended for the sole purpose of establishing the physical

dimensions of screw-thread products. While under tolerances

various grades of workmanship are covered, it is not intended in

any way to specify or limit the material or physical qualities

required by the user. These specifications as to material and

physical qualities must be established according to individual

needs. Here again the importance of stating these requirements

in concise and definite specifications is emphasized.

2. classification of fits

There are established herein for general use, unless otherwise

specified, four distinct classes of screw-thread fits with subdivisions as specified in the following brief outline of the four classes. 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.

The examples given under each class of fit are for the purpose

of illustration only. It is not the intention of the commission to

arbitrarily 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 each class of fit are given in Tables

5 to 1 8, inclusive.
PROGRESS REPORT 23

Class I, loose fit.

Subdivision A

Class II, medium

fit.

Class III. close fit

Class IV, wrench

fit.

Includes screw-thread work of rough commercial

quality, where the threads must assemble readily,

and a certain amount of shake or play is not objectionable, such as artillery ammunition, hose

couplings, etc. ("Includes the great bulk of screw-thread work of

( ordinary quality of finished and semifinished

l regu ).

^ bolts and nuts, machine screws, etc. Subdivision B P

ncludes the better grade of interchangeable screw- special) I tnrea<i work, such as high grade automobile and

[ aircraft bolts and nuts. Includes screw-thread work requiring a fine snug

fit, somewhat closer than the medium fit special. In this class of fit selective assembly of parts may

be required.

I

Includes screw threads used in light sections with moderate stresses, such as aircraft and automobile-engine work. (Includes screw threads used in heavy sections with

heavy stresses, such as steam-engine and heavy

hydraulic work. On account of lack of data, tolerance and allowances are not

specified herein for Class IV, Wrench Fit.

(a) General Specifications.—The following general specifications will apply to all classes of fits hereinafter specified.

1. Uniform Minimum Nut.—In order to conform to the general

ideas of standardization the pitch diameter of the minimumthreaded hole or nut should correspond to the basic size, the

errors due to workmanship being permitted above the basic size.

2. Length of Engagement.—The maximum length of engagement for screw threads manufactured in accordance with any of

the classes of fit specified herein shall not exceed the quantity as determined in the following formula:

L=(i.5 ) D,

where L = length of engagement,

D = basic major diameter of thread.

3. Scope of Classification.—The specifications established for

the various classes of fit are applicable to the National Coarse

Threads, the National Fine Threads, the National Hose Threads,

Straight Pipe Threads, and to any special thread required in manufacture which is not intentionally tapered.

(b) Class I, Loose Fit.—The loose-fit class of screw threads

will be defined and specified as follows

:

1. Definition.—This class is intended to cover the manufacture

of strictly interchangeable threaded parts where the work is pro-
24 NATIONAL SCREW THREAD COMMISSION

duced in two or more manufacturing plants. In this class will be

included threads for artillery ammunition and rough commercial

work, such as stove bolts, carriage bolts, and other threaded work

of a similar nature, where quick and easy assembly is necessary

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

National Straight Pipe Threads and National Hose-Coupling

Threads are to be produced in this class of fit only. National

Fire-Hose Threads are to be produced in this class in accordance

with special allowances and tolerances for fire-hose coupling

threads, as given in Table 8. 2. Minimum Nut Basic.—The pitch diameter of the minimum

nut of a given diameter and pitch will correspond to the basic

pitch diameter as specified in the tables of thread systems given

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

thread to be manufactured. The pitch diameter of the minimum

nut is the theoretical pitch diameter for that size. 3. Maximum Screw Below Basic.1 —The dimensions of the maximum screw of a given pitch and diameter will be below the basic

dimensions as specified in the tables of thread systems given

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

threads to be manufactured, by the amount of the allowance

given in Table 5. 4. Direction of Tolerance on Nut.—The tolerance on the nut

will be plus; to be applied from the basic size to above basic size.

5. Direction of Tolerance on Screw.—The tolerance on the screw

will be minus; to be applied from the maximum screw dimension

to below the maximum screw dimension.

6. Allowance Values.—The allowance provided between the

size of the minimum nut, which is basic, and the size of the maximum screw for a screw thread of a given pitch, will be as specified

in Table 5. 7. Tolerance Values.—The tolerance allowed on a screw or nut

of a given pitch will be as specified in Table 5.

1 The maximum minor diameter of the screw is above the basic minor diameter, as shown in Fig. 7.
PROGRESS REPORT 25

Z OOSJE" FtTT

CLCARAKCe-S /jLl.LtSTBAT£0 FOR.

/"— & ST/ZD

7l - Bas/c thread

' = ttPTH of T/eury-

= 0/08Z53p

3/=>S/c S/ZE

FlG. 7.Illustration of tolerance and allowance {neutral space) for Class I, loose fit

PROGRESS REPORT 27

NoTE.—Dotted line shows basic size.

f=0.00 54=Basic depth of D=Major diameter

truncation E=Pitch diameter

h= .0325=Basic thread K=Minor diameter

depth

FlG. g.

Illustration of loosest condition for Class I, loose fit, y£ inch, 20 threads
28 NATIONAL, SCREW THREAD COMMISSION

5 *M NOTATION

/=0.0054=Basic depth of

truncation

h= .0325=Basic thread

depth

Fig. io.—Illustration of tightest condition for Class I, loose fit, % inch, 20 threads

D=Major diameter

E—Pitch diameter

K=Minor diameter
PROGRESS REPORT 29

TABLE 5.—Class I, Loose Fit, Allowances and Tolerances for Screws, Nuts, Gages,

and Hose Couplings

1 2 3 4 5 • 6 7

Threads per inch Allowances

Extreme or drawing pitch diameter

tolerances

Master-gage tolerances Net pitch diameter

tolerances Diameter Lead b J£ angle

Inch Inch Inch Inch Deg. Min. Inch

80 0. 0007 0. 0024 0. 0002 ±0.0002 ±0 30 U. Uu£U

72 . 0007 . 0025 .0002 ± 0002 ±0 30 . 0021

64 !ooo7 !0026 0002 ± 0002 ±0 30 '.0022 56 .0008 .0028 !ooo2 ± 0002 ±0 30 .0024

48 . 0009 . 0031 .0002 ± 0002 to 30 . 0027

44 .0009 . 0032 .0002 ± 0002 ±0 30 . 0028

40 . 0010 . 0034 .0002 ± 0002 ±0 20 . 0030

36 !oon !0036 . 0002 ± 0002 ±0 20 !o032 32 .0011 .0038 !ooo2 ± 0002 ±0 20 .0034

28 . 0012 . 0043 .0003 ± 0002 ±0 15 . 0037

24 . 0013 .0046 .0003 ± 0002 ±0 15 . 0040 20 . 0015 . 0051 .0003 ± 0002 ±0 15 . 0045

18 !ooi6 !o057 .0004 ± 0003 ±0 10 !o049

16 .0018 .0063 .0004 ± 0003 ±0 10 .0055

14 .0021 .0070 .0004 ± 0003 ±0 10 .0062

13 .0022 .0074 .0004 ± 0003 ±0 10 .0066

12 .0024 .0079 .0004 ± 0003 ±0 10 .0071

11 .0026 .0085 .0004 ± 0003 ±0 10 .0077

10 .0028 .0092 .0004 ± 0004 ±0 5 .0084

9 .0031 .0100 .0004 ± 0004 ±0 5 .0092

8 .0034 .0111 .0004 ± 0004 ±0 5 .0103

7 .0039 .0124 .0004 ± 0004 ±0 5 .0116

6 .0044 .0145 .0006 ± 0005 ±0 5 .0133 5 .0052 .0169 .0006 ± 0005 ±0 5 .0157 4i .0057 .0184 .0006 ± 0005 ±0 5 .0172

4 .0064 .0204 .0006 ± 0005 ±0 5 .0192

"See "VI. Gages."

6 Allowable variation in lead between any two threads not farther apart than the length of engagement.
30 NATIONAL SCREW THREAD COMMISSION

os « E n Bii

tv O OH iH N gOHOOHH

jad '

* *

o woinom oocoo ooooo o oo

toooTfowovo NviNON in o m o in ooooo ooo d h in Hixnoa r\j m r- o cm m o in o in o m o r-< h (M cm co co --j- m in ^omcoh nuinon in o

So • • • •

co cn vo vo co cm co co in tj- hhnnn cocotfinm IOMJiOh o o co m m co oo m o o _ _ _

oo

ess co din o mom m t — ' - — - o co m oo o

r . ^ S O CO S So ' '

•

co co o o md lomNkom <o cm o o co notoo ooo O vo co d co vo d cm in oo i-< r-» co d in o oo ^ o vo co oo oo tVOOHHVl HN^-OVO CO m CO O CO H UD r-H£J H^H <-i h h mm co co in m ^onodoh Nint^-Oro m t-» o HH H H H CM CM N N CO

JJiflNOOOlH

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So

a

in m m m o h r-« «-h co «hNNCOCM NOOOt^lO

CM IO d CM COtOM/lH

rHiH pHrHpg CMCOCO-^-m

1

- CM 00 d vO iflNOHrt OOO Tj- CM CTi Ollflt^U-'t 00 00 OO

• ffiHtM't voocor-cM mom 1 vo co d O HtnocoH co vo co

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d Tt- m oo oo

cm tj- in oo SgSSSS

So ' *

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r-- d_ d_ in -<J- Tf- r-c O T}- O O 00 CO N (\J 1^. -H [> Cv VO VDVO r»coNooN vof hoco vo m cm co cm r-. h o in in r»c-c*» i-i^voooth r- co d in o vo co o i—< co in d cm in o co oo co

»-1 1~* < >—< cm cm co co "^f" m m vo co d o ^miocon co m oo H »—5 »—5 •—< >—< CM (M CM (M

00 vO vO vO

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So •

•

•

tmo cm oo oo vo >—i m m u- -»3- Tt- vo cm vo oo m o r- m co co vo vo vo comor^oo

IT) i-icomcoco mom (DNCO Ol HCOlflNO CM LO oi-J 1-J t-i H CVJ CM fM CM

.—< t-- rj- d d vo vo vo r- wmvoNcoov

2 o o o o o So •

•

CM CM d d d CO CM f- CO TTOI-Om NInOvON O CO *N d IOOiQhN w H H CM CO CO •>*•

vO r* I> t>. -fl- N^invON

in vo £*» oo d

Tj- vo in ^ Tf Tj- mdcodd ddd d i—• co m o CM c— CM ocomc-o cm t>- H i-i h H N CM CM CM*

tJ-CMC^-h^

r _ d d r- in co

x5 tj- in «d oo 2 o o o o o

m m o o ONvoinc?

cm oo vo oo co m m o co dHcoinr- co oo co d O H H t-H H cm cm co co ^j- h «o ~* cm cm rj- n- COTT0OI>t> CO OO CO

tj- vo vo oo co u- d O CM T O d i—I CO VO H H H H H CM CM CM

i-i co in co co

Xh CO CO CM O CO

cu m vo r- oo d

jjj] o o o o o yd ' ' "

"

vovovovocm t--moo^j-d d m vo cm co

co 1-- co r- tMvot^-cot^ o m co in d cm co vo oo ^a-dTrom ripoco*-* o -<-« i-h i-i cm cm co «*- in vo c- co d

c- d d cm c*. VO vO vo

t-> TT VO

I a>a

vo co m tjaj m d» oo d O jS o o o o H 3tj-tj- mvot>do d co o vo vo OCMCOHH

tj- o- d co co

1—" co m oo o

CM VO VO CO CO W (M CO "fl" c*-

_£h O O O O H

vo vO vO vO O

H CM CM CM CM

<—< VO d CM CM

ca r- d >—< tJ- j)voncj\oh jgOOOHH . _ - . o cm m c- d CM CO m VDNCOOtO

co vo o m in co oo c i—< »o —> o- r-< cm cm c cm vo r—i m o in o i CM ^" t>- d CM U-t-C

1—5 1—3 t-H i—5 CM CM CM C

CO CM O O

c/i cm in oo i-c

fll ("- OO d i—• CM JgOOO HH

d d r- r>. in d cm oo h ti- cm d vo h

vo <m co rj- co ocomt>o CMt-HvOH covooohtj- h r> co d vo cM-^-c^dcM H i—I i—I CM CM CO CO -3- m VO t-« 00 d H H VO 00 CO CO vo m -"i- tj- d T d tj- CM U- t>. CM

* H CM CM C

c- vo in

h cm co m «»f c CM CM CM CM CO
PROGRESS REPORT 31

it!

1

I

s"

1

1

9

8

,§S§S3 ***** 1111 IIIII IIII

Jills IIIII IIIII IIIII IIII

illlll lllll IIIII IIIII IIIII IIII

iiiiii mis 11111 iisii mil 1111

3

I

illlli IIIII IIIII IIIII Hill IIII

IpIII IIII! mi 11111 11111 1111

illlll lllls IIIII IIIII IIIII IIII

illlli Illli IIIII IIIII IIIII IIII

lllil IIIII IIIII IIIII IIIII IIII ^^^^^ NNNN

IpIII Islfl iini 11111 11111 mi

Iplil lllil IIIII lllil IIIII IIII

11111 mn mm 11111 11111 1111

IIII IIIII IIPI IIII

SSSSS JSSSS 22222 222s

I

g1

EI5

II

11

1

ft

1!

If
32 NATIONAL SCREW THREAD COMMISSION

TABLE 8.—National Fire-Hose Couplings, Thread Dimensions

COUPLING THREAD

Major diameter Pitch diameter Minor diameter Nominal Threads Pitch Depth of size per inch thread Max. Min. Max. Min. Max. Min.

Inch Inch Inches Inches Inches Inches Inches Inches

2.5000.

.

7.5 0. 13333 0. 09547 3. 1183 13.0992 3.0094 2.9970 2.9263 2.9015 3.0000 6.0 . 16667 . 12434 3. 6829 a 3. 6617 3. 5451 3. 5306 3.4353 3.4063

3. 5000 6.0 . 16667 . 12434 4.3079 a 4. 2867 4. 1701 4. 1556 4.0603 4.0313 4.5000 , 4.0 .25000 . 17651 5. 8470 a 5. 8133 5.6439 5.6235 5.4878 5.4470

NIPPLE THREAD

2.5000.

,

7.5 0. 13333 0. 09547 3. 0625 3.0377 2.9670 2.9546 a 2. 8715 2.8591

3.0000,

.

6.0 . 16667 . 12434 3. 6250 3. 5960 3. 5006 3. 4861 a 3. 3763 3.3618

3. 5000 6.0 . 16667 . 12434 4.2500 4.2210 4. 1256 4.1111 « 4. 0013 3.9868 4.5000 4.0 .25000 . 17651 5. 7500 5. 7092 5. 5735 5. 5531 a 5. 3970 5. 3763

"Dimensions given are figured to the intersection of the worn tool arc with a center line through crest and

root. The dimensions given in the tables of coupling and nipple sizes are the limiting dimensions of the work and not of the gages. TABLE 9.—National Hose Couplings, Thread Dimensions

COUPLING THREAD

Major diameter Pitch diameter Minor diameter Nominal Threads Depth of size per inch Pitch thread Max. Min. Mas. Min. " Max. Min.

Inch Inch Inches Inches Inches Inches Inches Inches H ny2 0. 08696 0.05648 1.0936 a 1. 0788 1. 0245 1.0160 0. 9765 0.9595

l ny2 .08696 . 05648 1. 3262 a 1.3114 1.2571 1.2486 1.2091 1.1921 1M ny2 .08696 . 05648 1.6710 a 1. 6562 1.6019 1. 5934 1.5539 1.5369 m ny2 .08696 . 05648 1.9099 a 1.8951 1. 8408 1.8323 1. 7929 1.7759 2 ny2 . 08696 . 05648 2.3839 a 2. 3691 2. 3148 2.3063 2.2668 2. 2498

NIPPLE THREAD

% ny2 0. 08696 0. 05648 1. 0625 1. 0455 1. 0060 0. 9975 0.9495 0. 9410

1 uy2 . 08696 . 05648 1.2951 1.2781 1.2386 1.2301 a 1. 1821 1. 1736 m ny2 . 08696 . 05648 1.6399 1. 6229 1.5834 1.5749 a 1. 5269 1. 5184 iy2 ny2 .08696 . 05648 1.8788 1.8618 1.8223 1.8138 a 1. 7659 1. 7574

2 ny2

. 08696 . 05648 2.3528 2.3358 2.2963 2. 2878 a 2. 2398 2.2313

o Dimensions given are figured to the intersection of the worn tool arc with a center line through crest and

root. The dimensions given in the tables of coupling and nipple sizes are the limiting dimensions of the work and not of the gages.
PROGRESS REPORT 33

(c) Class II-A, Medium Fit (Regular).—This class of screw- threads will be defined and specified as follows:

/. Definition.—The medium-fit class, Subdivision A, Regular,

is intended to apply to interchangeable manufacture where the

threaded members are to assemble nearly, or entirely, with the

fingers and where a moderate amount of shake or play between

the assembled threaded members is not objectionable. This

class will include the great bulk of fastening screws for instruments, small arms, and other ordnance material, such as gun carriages, aerial bomb-dropping devices, and interchangeable ac- cessories mounted on guns; also machine screws, cap screws, and

screws for sewing machines, typewriters, and other work of a

similar nature.

2. Minimum Nut Basic.—The pitch diameter of the minimum

nut of a given diameter and pitch will correspond to the basic

pitch diameter as specified in tables of thread systems given

herein which is computed from the basic major diameter of the

thread to be manufactured.

3. Maximum Screw Basic.—The major diameter and pitch

diameter of the maximum screw of a given pitch and diameter

will correspond to the basic dimensions as specified in tables of

thread systems given herein which are computed from the basic

major diameter of the thread to be manufactured.

4. Direction of Tolerance on Nut.—The tolerance on the nut will

be plus; to be applied from the basic size to above basic size. 5. Direction of Tolerance on Screw.2—The tolerance on the screw

will be minus ; to be applied from the maximum size to below maximum size.

6. Zero Allowance.—The allowance between the pitch diameter

of the maximum screw and the minimum nut will be zero for all pitches and all diameters.

7. Tolerance Values.—The tolerance for a screw or nut of a

given pitch will be as specified in Table 10.

The maximum minor diameter of the screw is above the basic minor diameter, as shown in Fig. n. 12071 °-=21- 3
34 NATIONAL SCREW THREAD COMMISSION

CjLASsW/lvRPErJJLARVSPECfAtMFniUfilFlT.

» AL L O W/?A/f£,% 41AID

t Jl-i. U-5TfZ/*TED /=•<=>/g

^Z?= P/TGH

•f =JDE*>r*i TftVrtCAT/OH

R©. II.

Illustration of tolerance and allowance for Classes II-A and II-B, medium fit
PROGRESS REPORT
36 NATIONAL SCREW THREAD COMMISSION

MOTE: GOTT£n LINE <5HOhY*5 SASfC <S/2Z^

NOTATION

/=0.0054=Basic depth of D=Major diameter

truncation E=Pitch diameter

h= .0325=Basic thread K^Minor diameter

depth

Fig. 13.

Illustration of loosest condition for Class II-A, medium fit regular, % incK

20 threads
PROGRESS REPORT 37

NOTATION

/=0.0054=Basic depth of

truncation

h= .0325 =Basic thread depth

D=Major diameter

E=Pitch diameter

K=Minor diameter

FlG. 14.Illustration of tightest condition for Class II-A, medium fit regular and Class II-B, medium fit special, % inch, 20 threads
38 NATIONAL SCREW THREAD COMMISSION

TABLE 10.—Class II-A, Medium Fit (Regular), Allowances and Tolerances for Screws, Nuts, and Gages

1 2 3 4 5 6 7

Threads per inch Allowances

Extreme or drawing pitch diameter

tolerances

Master-gage tolerances a Net pitch diameter

tolerances Diameter Lead & § angle

T t. Inch Inch Inch Inch Deg. Min. Inch

ft ftnnn 0. 0017 n ftnfti 0- 0UU2 ±0.0002 ±0 30 0013

72 .0000 .0018 .0002 ± 0002 ±0 30 i0014 64 .0000 .0019 .0002 ± 0002 ±0 30 .0015 56 0000 . 0020 .0002 ± 0002 ±0 30 0016

oooo . 0022 .0002 ± 0002 ± 30 0018

44 0000 . 00_ 3 . 0002 ± 0002 ±0 30 . 0019

40 ioooo .0024 .0002 ± 0002 ±0 20 !0020

36 .0000 .0025 .0002 ± 0002 ±0 20 .0021

32 9999 . 0027 .0002 ± 0002 ±0 20 0023 28 . oooo . 0031 .0003 ± 0002 ±0 15 0025

24 . 0000 . 0033 .0003 ± 0002 ±0 15 0027 20 .0000 .0036 .0003 ± 0002 ±0 15 !(H)30 18 .0000 .0041 .0004 ± 0003 ±0 10 .0033

16 .0000 .0045 .0004 ± 0003 ±0 10 .0037 14 .0000 .0049 .0004 ± 0003 ±0 10 .0041

13 .0000 .0052 .0004 ± 0003 ±0 10 .0044

12 .0000 .0056 .0004 ± 0003 ±0 10 .0048

11 .0000 .0059 .0004 ± 0003 ±0 10 .0051

10 .0000 .0064 .0004 ± 0004 ±0 5 .0056

9 .0000 .0070 .0004 ± 0004 ±0 5 .0062

8 .0000 .0076' .0004 ± 0004 ±0 5 .0068

7 .0000 .0085 .0004 ± 0004 ±0" 5 .0077

6 .0000 .0101 .0006 ± 0005 ±0 5 .0089

5 .0000 .0116 .0006 ± 0005 ±0 5 .0104 4J .0000 .0127 .0006 ± 0005 ±0 5 .0115

4 .0000 .0140 .0006 ± 0005 ±0 S .0128

a See "VI. Gages."

6 Allowable variation in lead between any two threads not farther apart than the length of engagement.
PROGRESS REPORT 39

a "1

sssaiQ ssssal BgSls sIrss lllll ill gogsaa assss sssss ssasa sssgs ses

-ai11

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. 11

12

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.

2805

.3389 .3960 .4552 .5140 .5719 .6914 .8098 .9264 1.

0407 1.

1657

1.

4018

1.

6317

1.

8684 2.

1184

2.

3516

2.

6016

2.

8516

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s

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NATIONAL SCREW THREAD COMMISSION

lesss s§is§ mil mil §§in 1111

i

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mis iiiii iiiii iiiii mil mm

mil siiii nils iiiii iii§§ iiii

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PROGRESS REPORT 41

(d) Class II-B, Medium Fit (Special).—This class of screw

threads will be defined and specified as follows:

1. Definition.—The medium-fit class, Subdivision B, Special, is intended to apply especially to the higher grade of automobile

screw-thread work. It is the same in every particular as Class

II-A, Medium Fit (Regular), except that the tolerances are

smaller.

2. Minimum Nut Basic.—The pitch diameter of the minimum

nut of a given diameter and pitch will correspond to the basic

pitch diameter as specified in tables of thread systems given herein

which is computed from the basic major diameter of the thread

to be manufactured.

3. Maximum Screw Basic.—The major diameter and pitch diameter of the maximum screw of a given pitch and diameter will cor- respond to the basic dimensions as specified in tables of thread

systems given herein which are computed from the basic major

diameter of the thread to be manufactured.

4. Direction of Tolerance on Nut.—The tolerance on the nut

will be plus; to be applied from the basic size to above basic size.

5. Direction of Tolerance on Screw.3—The tolerance on the screw

will be minus; to be applied from the maximum size to below

maximum size.

6. Zero Allowance.—The allowance between the pitch diameter

of the maximum screw and the minimum nut will be zero for

all pitches and all diameters.

7. Tolerance Values.—The tolerance for a screw or nut of a

given pitch will be as specified in Table 13.

3 The maximum minor diameter of the screw is above the basic minor diameter, as shown in Fig. u.
42 NATIONAL SCREW THREAD COMMISSION
PROGRESS REPORT 43

A/& 7~£r: DorTED L 1NB SHOWS BAS/C S/Z£

NOTATION

/=0.0054=Basic depth of D=Major diameter

truncation E=Pitch diameter

h= .0325=Basic thread X=Minor diameter

depth

Fig. 16.Illustration of loosest conditionfor Class II-B, mediumfit special. For illustra- tion of tightest conditionfor Class II-B, see Fig. 14, p. 37, % inch, 20 threads
44 NATIONAL SCREW THREAD COMMISSION

TABLE 13.—Class II-B, Medium Fit (Special), Allowances and Tolerances for Screws, Nuts, and Gages

1 2 3 4 5 6 7

Threads per inch Allowances All Extreme or drawing pitch diameter

tolerances

Master-gage tolerances

jn et pitcu diameter

tolerances Diameter Lead 6 M angle

Inch Inch Inch Inch Dee. Min. Inch

80 0. 0000 0.0013 0. 0002 ±0. 0002 ±0 30 0. 0009

72 .0000 .0013 .0002 ± .0002 ±0 30 .0009

64 .0000 .0014 .0002 ± .0002 ±0 30 .0010

56 .0000 .0015 .0002 ± .0002 ±0 30 .0011 48 .0000 .0016 .0002 ± .0002 ±0 30 .0012

44 .0000 .0016 .0002 ± .0002 ±0 30 .0012

40 .0000 .0017 . 0002 ± .0002 ±0 20 .0013

36 .0000 .0018 .0002 ± .0002 ±0 20 .0014

32 .0000 .0019 .0002 ± .0002 ±0 20 .0015 2C .0000 .0022 . 0003 i . 0002 ±0 15 .0016

24 .0000 .0024 .0003 ± .0002 ±0 15 .0018

20 .0000 .0026 .0003 4- .0002 ±0 15 .0020

18 .0000 .0030 .0004 ± .0003 ±0 10 .0022

16 .0000 .0032 .0004 ± .0003 ±0 10 .0024

14 .0000 .0036 .0004 ± .0003 ±0 10 .0028

13 .0000 .0037 .0004 ± .0003 ±0 10 .0029

12 .0000 .0040 .0004 ± .0003 ±0 10 .0032

11 .0000 .0042 .0004 ± .0003 ±0 10 .0034

10 .0000 .0045 .0004 ± .0004 ±0 5 .0037

9 .0000 .0049 .0004 ± .0004 ±0 5 .0041

8 .0000 .0054 .0004 ± .0004 ±0 5 .0046

7 .0000 .0059 .0004 ± .0004 ±0 5 .0051

6 .0000 .0071 .0006 ± .0005 ±0 5 .0059

5 .0000 .0082 .0006 ± .0005 ±0 5 .0070 4^ .0000 .0089 .0006 ± .0005 ±0 5 .0077

4 .0000 .0097 .0006 ± .0005 ±0 5 .0085

a See "VI. Gages."

& Allowable variation in lead between any two threads not farther apart than the length of engagement.
if]

ii

PROGRESS REPORT

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45

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NATIONAL SCREW THREAD COMMISSION

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M gS|g| SgSgS ggggg SSSgg S|||§ ssss

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PROGRESS REPORT 47

(e) Class III, Close Fit.—The close-fit class of screw threads

will be defined and specified as follows:

1. Definition.—This class is intended for threaded work of the

finest commercial quality, where the thread has practically no

back lash, and for light screwdriver fits. In the manufacture of

screw-thread products belonging in this class it will be necessary

to use precision tools, selected master gages, and many other re- finements. 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 neces- sary in some cases to select the parts when the product is being

assembled.

2. Minimum Nut Basic.—The pitch diameter of the minimum

nut of a given diameter and pitch will correspond to the basic

pitch diameter as specified in tables of thread systems given herein

which is computed from the basic major diameter of the thread

to be manufactured.

j. Maximum Screw Above Basic.—The major diameter and

pitch diameter of the maximum screw of a given diameter and

pitch will be above the basic dimensions as specified in tables of

thread systems given herein which are computed from the basic

major diameter of the thread to be manufactured by the amount

of the allowance (interference) specified in Table 16.

4. Direction of Tolerance on Nut.—The tolerance on the nut

will be plus ; to be applied from the basic size to above basic size.

5. Direction of Tolerance on Screw.—The tolerance on the screw

will be minus; to be applied from the maximum screw dimensions

to below the maximum screw dimensions.

6. Allowance Values.—The allowance (interference) provided

between the pitch diameter of the minimum nut, which is basic,

and that of the maximum screw, which is above basic, will be as

specified in Table 16.

7. Tolerance Values.—The tolerance for a screw or nut of a

given pitch will be as specified in Table 16.
48 NATIONAL, SCREW THREAD COMMISSION

CLASSJK - Close. F> t

. Allownc£s, *f*o CL£APAr<e£.$

'"-3 Thread

FlG. 17.

Illustration of tolerance and allowance (interference) for Class III, close fit
PROGRESS REPORT 49

12071°—21-
5° NATIONAL, SCREW THREAD COMMISSION

/vote: dotted L /ne Shocks e/is/c S/zrE

NOTATION

/=0.0054=Basic depth of

truncation

.0325=Basic thread

depth

h=

D=Major diameter

E=Pitch diameter

K=Minor diameter

Fig. 19.

Illustration of loosest conditionfor Class III , close fit, inch, 20 threads
PROGRESS REPORT 5

1

NOTATION

/=0.00 54=Basic depth of D=Major diameter

truncation E—Pitch diameter

h= .0325=:Basic thread K=Minor diameter

depth

Fig. 20.Illustration of tightest conditionfor Class III, close fit, % inch, 20 threads
52 NATIONAL SCREW THREAD COMMISSION

TABLE 16.—Class III, Close Tit, Allowances and Tolerances for Screws, Nuts, and

Gages

1 2 3 4 5 6 7

Threads per inch

Interference

or negative allowances

Extreme or drawing pitch diameter

tolerances

Master-gage tolerances " Net pitch diameter

tolerances Diameter Lead f> angle

Inch Inch Inch Inch Min. Sec. Inch

80 0. 0001 0. 0006 0. 0001 ±0.0001 ±15 00 0.0004

72 .0001 .0007 .0001

'

± 0001 ±15 00 .0005

64 .0001 .0007 .0001 0001 ±15 00 .0005

56 0002 0007 .0001 ± 0001 ±15 00 0005

48 !o002 .0008 . 0001 ± 0001 ±15 00 ]0006

44 .0002 .0008 . 0001 ± 0001 ±15 00 .0006 40 .0002 .0009 . 0001 ± 0001 ±10 00 .0007 36 .0002 .0009 .0001 ± 0001 ±10 00 .0007

32 0002 . 0010 .0001 ± 0001 ±10 00 0008 28 .0002 .0011 .00015 ± 0001 ± 7 30 iooos

24 .0003 .0012 .00015 ± 0001 ± 7 30 .0009 20 .0003 .0013 .00015 ± 0001 ± 7 30 .0010

18 .0003 .0015 .0002 ± 00015 ± 5 00 .0011

16 0004 0016 .0002 ± 00015 ± 5 00 0012

14 !0004 .0018 .0002 ± 00015 ± 5 00 !ooi4

13 . 0004 .0019 .0002 ± 00015 ± 5 00 .0015

12 .0005 .0020 .0002 ± .00015 ± 5 00 .0016

11 .0005 .0021 .0002 ± 00015 ± 5 00 .0017

10 .0006 .0023 .0002 ± 0002 ± 2 30 .0019 9 .0006 .0024 .0002 ± 0002 ± 2 30 .0020

8 .0007 .0027 .0002 ± 0002 ± 2 30 .0023

7 .0008 .0030 .0002 ± 0002 ± 2 30 .0026

6 .0009 .0036 .0003 ± 00025 ± 2 30 .0030

5 .0010 .0041 .0003 ± 00025 ± 2 30 .0035 4Ji .0011 .0044 .0003 ± 00025 ± 2 30 .0038

4 .0013 .0048 .0003 ± 00025 ± 2 30 .0042

a See "VI. Gages."

6 Allowable variation in lead between any two threads not farther apart than the length of engagement
PROGRESS REPORT 53

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NATIONAL SCREW THREAD COMMISSION

4> ToTM •

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PROGRESS REPORT 55

(/) Class IV, Wrench Fit.—The wrench-fit class of screw

threads will be defined and specified as follows:

1. Definition.—This class is intended to cover the manufacture

of threaded parts one-fourth inch diameter or larger which are to

be set or assembled permanently with a wrench. Inasmuch as for

wrench fits, the material is an important factor in determining the

fit between the threaded members, there are provided herein two

subdivisions for this class of work, namely, Subdivision A and

Subdivision B. These two subdivisions differ mainly in the

amount of the allowance (interference) values provided for dif- ferent pitches.

Subdivision A of Class IV, Wrench Fit, provides for the production of interchangeable wrench-fit screws or studs used in light

sections with moderate stresses, such as for aircraft and automobile engine work.

Subdivision B of Class IV, Wrench Fit, provides for the production of interchangeable wrench-fit screws or studs used in

heavy sections with heavy stresses, such as for steam-engine and

heavy hydraulic work.

2. Minimum Nut Basic.—The pitch diameter of the minimum

nut of a given diameter and pitch for threads belonging in either

Subdivision A or Subdivision B will correspond to the basic pitch

diameter as specified in tables of thread systems given herein,

which is computed from the basic major diameter of the thread

to be manufactured.

j. Maximum Screw above Basic.—The major diameter and pitch

diameter of the maximum screw of a given diameter and pitch

for threads belonging in either Subdivision A or Subdivision B

will be above the basic dimensions as specified in tables of thread

systems given herein, which are computed from the basic major

diameter of the thread to be manufactured, by the amount of the

allowance (interference) provided.

4. Direction of Tolerance on Nut.—The tolerance on the nut

will be plus; to be applied from the basic size to above basic size.

5. Direction of Tolerance on Screw.—The tolerance on the screw

will be minus ; to be applied from the maximum screw dimensions

to below maximum screw dimensions.

6. Allowance and Tolerance Values not Included.—At the present

time the commission does not have sufficient information or data

to include in its progress report values for tolerances and allow ances for wrench fits. It is hoped, however, that sufficient information resulting from investigation and research will enable the
56 NATIONAL SCREW THREAD COMMISSION

commission to decide, at an early date, the allowance and toler- ance values for the two classes of wrench fits included herein,

which will be applicable to the various materials and which will

meet the requirements found in manufacture of machines or product requiring wrench fits.

3. TOLERANCES

There are specified herein for use in connection with the various

fits established, three different sets of tolerances as given in Tables

5, io, 13, and 16.

(a) Tolerances Represent Extreme Variations.—The tol- erances as hereinafter specified represent the extreme variations

allowed on the work.4

(b) Pitch Diameter Tolerances Include Lead and Angle

Variations.—The tolerance limits established represent, in reality,

the sizes of the "Go" and "Not Go" master gages. Errors in

lead and angle which occur on the threaded work can be offset by

a suitable alteration of the pitch diameter of the work. If the

"Go" gage passes the threaded work interchangeability is secured

and the thread profile may differ from that of the "Go" gage in

either pitch diameter, lead, or angle. The " Not Go " gage checks

pitch diameter only, and thus insures that the pitch diameter is such that the fit will not be too loose. (See Appendix 5 for further explanation.)

(c) Class I and Class II Tolerances Permit the Use of

Commercial Taps.—The tolerances established for Class I, Doose

Fit, and Class II, Medium Fit, permit the use of commercial taps

now obtainable from various manufacturers. For Class III,

Close Fit, in which it is desired to produce a hole close to the basic

size, it is recommended that a selected tap be used.

(d) Pitch Diameter Tolerances on Screw Same as on Nut.—

The pitch diameter tolerances provided for a screw of a given

class of fit will be the same as the pitch diameter tolerances provided for a nut corresponding to the same class of fit.

(e) Tolerances 6n Major Diameter of Screw Twice the

Pitch Diameter Tolerances.—The allowable tolerances on the

major diameter of screws of a given classification will be twice the

tolerance values allowed on the pitch diameters of screws of the same class.

(/) Tolerances on Minor Diameter of Screw.—The minimum minor diameter of a screw of a given pitch will be such as to

* Recommendations and explanations regarding the application of tolerances are given in Appendix 5.
PROGRESS REPORT 57

result in a basic flat (}4 X p) at the root when the pitch diameter

of the screw is at its minimum value. (Note.—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.)

The maximum minor diameter 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.

(g) Tolerances on Major Diameter op Nut.—The maximum

major diameter of the nut of a given pitch will be such as to result

in a flat one-third of the basic flat X p) when the pitch diameter

of the nut is at its maximum value. (Note.—When the minimum

nut is basic, the 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.)

The nominal minimum major diameter of a nut will be above

the basic major diameter by an amount equal to one-ninth of the

basic thread depth plus the neutral space. This results in a

clearance which is provided to facilitate manufacture by permitting a slight rounding or wear at the crest of the tap. In no case, however, should the minimum major diameter of the nut, as re- sults 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.

(h) Tolerances on Minor Diameter of Nut.—The tolerances on minor diameter of a nut of a given pitch will be one-sixth of the

basic thread depth regardless of the class of fit being produced.

Xi) Illustration. —In Fig. 21 there are shown the various re- lations previously specified for tolerances on both the screw and

the nut.

(j) Scope op Tolerance Specifications.—The specifications

establishing the various sets of tolerances for the different classes

of fit specified herein will apply to the manufacture of National

Coarse Threads, National Fine Threads, National Hose-Coupling

Threads, National Fire-Hose Coupling Threads, Straight Pipe

Threads, and wherever applicable to the production of all special

threads.
58 NATIONAL SCREW THREAD COMMISSION

Where tolerances are desired for a special thread and the pitch

is not listed in the tables given, the tolerance values should be

chosen corresponding to the number of threads per inch nearest

to that of the special thread being produced. Where the number

of threads per inch is midway between two of the pitches listed,

the tolerance corresponding to the coarser pitch should be used.

For instance, the tolerance on a screw having \i}4. threads per

inch would correspond to the tolerances specified for a screw of

ii threads per inch. VI. GAGES

1. INTRODUCTORY

For the production of interchangeable threaded parts in large

quantities, as provided for by specifications given under the

subject of "Classification and Tolerances," it will be necessary to

employ an adequate system of measuring or gaging the parts

produced.

It is not the desire of the commission, nor is it wise at the

present time, to lay down hard-and-fast specifications of a gaging

system to meet the requirements of various manufacturers. To

do this would not only cause hardship in certain lines of industry,

but also would tend to limit progress in this important subject

connected so closely with quantity production. It is felt, however, that inasmuch as at the present time the use of gages is the

only known means of securing interchangeability, it is wise,

especially in view of the experience and education gained during

the recent World War, that certain fundamentals should be

adopted which will serve as a unification of various gaging

systems now in use by manufacturers in this country. A complete gaging system which has been found adequate in the

production of war material is specified in detail in Appendix 6. (a) Fundamentals.—(i) Standard Master Gage is the gage to

which all other gages and all dimensions of the mating parts are ultimately checked or referred, either by direct check or by

comparative measurements.

It clearly establishes the low limit of the threaded hole and the

high limit of the screw at the point at which interference begins

between mating parts.

(2) The tolerance limits of the component as physically represented by the Limit Master Gages must never be exceeded as a

result either of errors or wear of the gages.
PROGRESS REPORT 59

(Drawing shows one side of thread only and therefore

spaces indicate half tolerances or tolerances on radii.)

Tol. major dia. screws=2xTol. pitch dia.

Tol. minor dia. screws=Tol. pitch dia. + 2/3 /

=Tol. pitch dia. + 1/9 /i Tol. major dia. nuts =Tol. pitch dia. +2/3 /

=Tol. pitch dia. + 1/9 h

Tol. minor dia. nuts =1/6 h

D=Major diameter

E=Pitch diameter

i<=Minor diameter

/=Depth of basic truncation

h—Depth of basic thread

Fig. 2i.

Relation between tolerance on pitch diameter, major diameter, and minor diameter
6o NATIONAL SCREW THREAD COMMISSION

(3) "Go" gages are absolutely essential to prevent interference

of mating parts.

(4) "Not Go" gages are essential to prevent excess shake,

play, or looseness of mating parts as determined by the extreme

component limits.

(6) Gage Classification: i. Standard Master Gage.—The

Standard Master Gage is a threaded plug representing as exactly

as possible all physical dimensions of the nominal or basic size of

the threaded component. In order that the Standard Master

Gage be authentic, the deviations of this gage from the exact

standard should be ascertained and certified by the National

Bureau of Standards and, when used, its known errors should

be taken into account.

2. Limit Master Gages.—The Limit Master Gages are threaded

plugs representing as nearly as possible the exact limiting physical

dimensions of the threaded mating parts as established by the

specified tolerances. (For further information on limit gages

see Appendix 6.) A complete set of Limit Master Gages, in the form of threaded

plugs, representing the maximum and minimum screw and nut

dimensions for both the coarse and the fine series, and for all classes of fit, should be standardized by and kept at the National

Bureau of Standards for use in settling any controversies that

may arise with reference to the dimensions of other Limit Master

Gages. The maximum ("Not Go") gages should be made to the

maximum pitch diameter only. The major diameter and minor

diameter should not be greater than the minimum specified for

the minimum ("Go") gages. (See Appendix 6 (c) (5).) 3. Inspection Gages.—Inspection gages are for the use of the

purchaser in accepting the product.

4. Working gages.—Working gages are those used by the

manufacturer to check the parts produced as they are machined.

(c) Standard Temperature.—Gages and product should have

their correct nominal dimensions at 68° F.

VII. NATIONAL PIPE THREADS

1. INTRODUCTORY

The material on the subject of pipe threads presented herewith was 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.
PROGRESS REPORT 6l

M. E. committee on International Standards for Pipe Threads.

It was published in October, 191 9, under the title of "Manual on American Standard Pipe Threads." It has been indorsed 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.

2. NATIONAL STANDARD PIPE THREADS

(Formerly known as American Standard Pipe Threads) Indorsed by:

Committee of Manufacturers on Standardization of Fittings and Valves, 1927-1928 Whitehall Building,

17 Battery Place, New York, N. Y. Chairman; Howard Coonley, Walworth Manufacturing Co., Boston,

Mass. Secretary: A. A. Ainsworth, 17 Battery Place, New York, N. Y.

Committee on Dimensions and Specifications: Chairman, A. M. Houser, Crane Co., Chicago, 111. Committee on Lists and Classifications: Chairman, J. S. Mattimore, The Kelly & Jones Co., New York, N. Y.

American Foundry & Construction Co., Pitts- burgh, Pa. American Valve Co., Coxsackie, N. Y.

Automatic Sprinkler Co. of America, 123 William

Street, New York, City. Crane Co., Chicago, 111. Darling Pump & Machinery Co. (Ltd.), Williamsport, Pa.

Detroit Brass Works, Detroit, Mich.

Detroit Lubricator Co., Detroit, Mich. Thomas Devlin Manufacturing Co., Philadelphia, Pa. Eddy Valve Co., Waterford, N. Y.

Essex Foundry, Newark, N. J. The Fairbanks Co., New York, N. Y.

Stanley G. Flagg & Co., Philadelphia, Pa.

General Fire Extinguisher Co., Providence, R. I. Illinois Malleable Iron Co., Chicago, 111. Jarecki Manufacturing Co., Erie, Pa. H. J. Kattenthaler, Philadelphia, Pa. The M. W. Kellog Co., New York, N. Y. The Kelly & Jones Co., New York, N. Y. The Kennedy Valve Manufacturing Co. N. Y. The Kerr Manufacturing Co., Walkerville,

tario, Canada. Kuhns Bros., Dayton, Ohio. Ludlow Valve Manufacturing Co., Troy, N. Y. The Lunkenheimer Co., Cincinnati, Ohio.

Malleable Iron Fittings Co., Branford, Conn.

T. McAvity & Sons (Ltd)., St. John, New Brunswick. McNab & Harlin Manufacturing Co., New York, N. Y.

Elmira,

OnNelson Valve Co., Philadelphia, Pa. Ohio Brass Co., Mansfield, Ohio.

Pacific Foundry Co., San Francisco, Calif. Pittsburgh Valve and Foundry Const. Co., Pitts- burgh, Pa. Pittsburgh Valve and Fittings Co., Barberton, Ohio. The Wm. Powell Co., Cincinnati, Ohio. The Pratt & Cady Co., (Inc)., Hartford, Conn. The Stockham Pipe Fittings Co., Birmingham,

Ala. Walworth Manufacturing Co., Boston, Mass. The D. T. Williams Co., Cincinnati, Ohio. R. D. Wood & Co., Philadelphia, Pa. Pipe Manufacturers:

National Tube Co'., Pittsburgh, Pa.

Central Tube Co., Pittsburgh, Pa. A. M. Byers Co., Pittsburgh, Pa. Wheeling Steel & Iron Co., Wheeling, W. Va. South Chester Tube Co., Chester, Pa. Jones & Laughlin Steel Co., Pittsburgh, Pa. Youngstown Sheet & Tube Co., Youngstown,

Ohio.

Steel & Tube Co. of America, Chicago, 111. U. S. Steel Products Co., New York, N. Y. Gage Manufacturers:

Pratt & Whitney Co., Hartford, Conn.

Greenfield Tap and Die Corporation, Greenfield, Mass.

Taft Peirce Manufacturing Co., Woonsocket, R. I.

History

The American Pipe-Thread Standard, also known as the American Briggs Standard, was formulated by Robert Briggs prior to 1882. Mr. Briggs for several years was superintendent of the Pascal Iron Works of Morris, Tasker & Co., Philadelphia, and later was engineering editor of the Journal of the Franklin Institute. After his death, a paper by Mr. Briggs containing detailed in- formation regarding American Pipe and Pipe-Thread practice was read before the

Institution of Civil Engineers of Great Britain. This is recorded in the Excerpt

minutes, Volume EXXI, Session 1882-1883, Part 1.
62 NATIONAL SCREW THREAD COMMISSION

While, in a general way, American manufacturers were threading practically to the Briggs Standard, in 1886 the manufacturers and the American Society of Mechanical Engineers jointly adopted it in detail, and master gages were made. The standard has since been in general use in the United States and Canada. At various conferences later, American manufacturers and the American Society

of Mechanical Engineers established additional sizes, certain details of gaging, tol- erances and special applications of the standard; also the formulas and dimensions were tabulated more completely than was originally done by Mr. Briggs.

Outline of Standard

The National (American) Pipe-Thread Standard establishes the following: Outside diameter of pipe,

Diameter of external (male) thread,

Diameter of internal (female) thread,

Profile of thread, Pitch or lead of thread,

Length of thread,

Taper of thread,

Engagement (by hand) of external and internal threads, Construction and use of gages, Tolerances, Use of taper threads, Use of straight threads. Tables of Dimensions

The dimensions of National (American) Pipe Threads are expressed in inches to one one-hundred thousandth (0.00001) of an inch, and in millimeters to one one- thousandth (0.001) of a millimeter. While this is a greater degree of accuracy than is ordinarily used, the dimensions

are so expressed in order to eliminate errors which might result from less accurate dimensions. The relation between the inch and the meter used in calculating the dimensions

in these tables is that established by law in the United States and on record in the Bureau of Standards, Department of Commerce, Washington, D. C. This is

1 meter=3o.37 inches exactly.

The metric equivalent of the inch resulting from this determination is

25.40005 millimeters= 1 inch. Outside Diameter of Pipe

The outside diameter of pipe is given in Column D of the table of dimensions. These

diameters should be very closely adhered to by pipe manufacturers. Diameter of Taper Thread

The pitch diameters of the taper thread are determined by formulas based on the

outside diameter of pipe and the pitch of thread. These are as follows: A=D-(o.osD+i.i)P.

B=A-\-o.o62$L1

. yl=pitch diameter of thread at end of pipe.

B=pitch diameter of thread at gaging notch. Z)=outside diameter of pipe.

L^normal engagement by hand between external and internal threads. P=pitch of thread.

Note.—The above formulas are not expressed in the same terms as the formula originally established by Mr. Briggs, because they are used to determine pitch diameters, whereas the Briggs formula determined

the major (outside) diameter of the thread. However, both forms give identical results.
PROGRESS REPORT 63

Profile

The angle between the sides of the thread is 6o° when measured in the axial plane,

and the line bisecting this angle is perpendicular to the axis of the pipe, for taper or

straight threads. (See Fig. 22.) The crest and root are truncated an amount equal to 0.033P. The depth of the

thread, therefore, is 0.8P. (See Fig. 22.) Note.—While Mr. Briggs originally advocated a slightly rounded crest and root, the thread as applied

in the manufacture of gages and thread tools has always been slightly flattened at the crest and root. While the crests on commercially manufactured external and internal threads would appear slightly rounded when examined with a microscope, for all practical purposes they may be considered as sharp. The roots of commercially manufactured threads are practically sharp when cut with new tools and

slightly rounded when cut with worn tools. Pitch

The pitch of a screw thread is the distance from a point on the thread to a corresponding point on the next thread, measured parallel to the axis.

Lead

The lead of a screw thread is the distance the screw will advance axially in one

revolution. It is expressed in terms of the number of threads in 1 inch and the number

of threads in 254 millimeters (254 mm equals 10 inches). On a single thread screw

the lead and pitch are identical.

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: L2 =(o.8D+6.8)P.

L2 =length of effective thread. £>=outside diameter of pipe.

P=pitch of thread.

Note.—The above formula is not expressed in the same terms as the one originally established by Mr.

Briggs, because it determines directly the length of effective thread which includes two threads slightly imperfect on the crest, whereas the Briggs formula determined the length of perfect thread, the two threads

imperfect on the crest not being included in the formula. However, both forms give identical results. Taper of Thread

The taper of the thread is 1 in 16 measured on the diameter.

Engagement Between Taper External (Male) and Internal (Female)

Thread

The normal length of engagement between taper external and internal threads when screwed together by hand is shown in Column Lx of Table 19. This length is controlled by the construction and use of the gages. Gages

Gages to properly maintain interchangeability of pipe threads should consist of Standard Master, Reference, Inspection, and Working Gages. The dimensions and

functions of these gages are outlined below.

Standard Master Gage

The Scandard Master Gage is a taper threaded plug gage. The roots of the threads

are cut to a sharp V or may be undercut below the sharp V to facilitate the making of the thread. The crests are truncated an amount equal to 0.1P. (SeeFig. 25.) Otherwise the gage is made to the dimensions given in Table 19. This gage is provided
64 NATIONAL SCREW THREAD COMMISSION

with the gaging notch as illustrated in Fig. 23. The Standard Master Gage is the gage

to which all other gages are ultimately referred either by transference of measure- ments or direct comparison by engagement. It is intended primarily for gage and

thread tool manufacturers. Reference Gages

The Reference Gages consist of a plug gage, similar in all respects to the Standard

Master Gage, and two ring gages. One ring gage has a thickness equal to dimension

Llt is the same diameter at the small end as the small end of the plug gage, and is flush with the plug gage at the small end and at the gaging notch when screwed on

tight by hand. (See Fig. 23.) The other ring gage has a thickness equal to dimension L2 , but is threaded for distance L2-L,. The distance equal to Lx is counterbored and unthreaded. This gage is the same diameter at the large end as the large end of the plug gage. (See Fig. 24.) The Reference Plug Gage is used to inspect inspection

and working taper threaded ring gages. The Reference Ring Gages are used to compare the reference plug with the standard master plug or the inspection and working

plug gages with the reference plug gage.

Inspection Gages

Inspection Gages consist of one taper threaded plug gage and one taper threaded

ring gage. The roots of the threads are cut to a sharp V or may be undercut to facili- tate making the thread. The crests are truncated an amount equal to 0.1P. (See

Fig. 27.)* The ring gage has a thickness equal to dimension Llt and the same diameter

at the small end as the small end of the plug gage. (See Fig. 26.) Note.—The object of truncating the crests on gages (truncation 0.1P) 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. Inspection Gages are for the use of the purchaser of pipe thread products. When

used, the extreme tolerance on the work should be applied. This tolerance is 1%

turns either way from the gaging notch in the case of internal threads inspected with

the inspection plug gage, and when inspecting external threads the tolerance is 1^

turns either way from the small end of the inspection ring. Working Gages

The Working Gages consist of one taper threaded plug gage 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 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. Gaging Internal (Female) Threads

The Inspection and Working Plug Gages, Figs. 31 and 34, 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. 'The

fitting or coupling is within the working or net tolerance if the working gage notch

is within one turn of the coupling or fitting face when screwed in tight by hand. In

the same way the coupling or fitting is within the inspection or extreme tolerance if the inspection gage notch is within 1% turns of the coupling or fitting face when

screwed on tight by hand.

This method of gaging is used either for taper internal threads or for straight internally threaded couplings which screw together with taper external threads. (See Figs. 31 and 34.)

4 Otherwise the gages are made to the dimensions given in Table 19.
PROGRESS REPORT 65

Gaging Taper External (Male) Threads

The ring gage, Fig. 26, should screw tight by hand on the pipe or external thread

until the small end of the gage is flush with the end of the thread. (See Fig. 28.) The pipe or external thread is within the working or net tolerance if the working gage

ring screws on until 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 zyi turns of the small end of the gage.Gage Tolerances

Master Gages.—Master Gages should be made with the narrowest possible limits

of error. In no case should the accumulative error exceed the total accumulative

tolerance on diameter given in Table 26. Each Master Gage should be accompanied

by a report showing the error on each of the elements of the thread and a statement

of the accumulative error derived from the errors in the various elements.

Reference Gages.—Column 1 of Table 26 gives the maximum allowable cumulation

of all errors in the thread surface of Reference Gages, expressed in terms of diameter,

and is illustrated in Fig. 37. No point in the thread surface of the gage should be

outside of the zone of tolerance indicated by the shaded portion of the illustration. Note.—This column is used when checking gages by measurement. If the errors in the gage are re- ported in terms of pitch, angle of thread, and diameter, Tables 28 and 29 may be used to determine the cumulation of these errors for comparison with Column 1. In Table 28 the results of errors in angle are expressed in terms of diameter. In Table 29 the results of errors in pitch are expressed in terms of di- ameter. For example: A J"—14 plug pipe thread gage is reported as follows: Pitch diameter, large end, 0.98881". Pitch diameter, small end, 0.96775". One-half included angle of thread, 29° 58'. Maximum error in lead, o. 00007". The correct pitch diameter at large end is 0.9S886". (See Table 19.) The error is 0.00005". The correct pitch diameter at small end is 0.96768". (See Table 19.) The error is 0.00007".

2' error in angle equals 0.00006". (See Table 28.) 0.00007" error in lead equals 0.00012". (See Table 29.) The cumulative error at large end in terms of diameter equals 0.00023". The cumulative error at small end equals 0.00025". The gage falls within the limits of the reference gage (0.00028" as given in Table 26.) Column 2 gives the equivalent of Column 1, expressed in terms of distance parallel

to the axis, and represents the maximum distance which a reference ring gage of perfect thickness or a reference plug gage of perfect length from small end to gaging notch may vary from being flush at the gaging notch or at the small end, when referred to basic dimensions. It is equal to 16 times Column 1, owing to the basic taper of 1 in

16, measured on the diameter.

Note.—This column is used when checking reference gages by comparison with a master gage. The

necessary allowance must be made for the error in the master. Column 3 gives the equivalent of Column 2, expressed in terms of the decimal part

of a turn from the basic dimensions.

Note.—This column is also used when checking reference gages by comparison with a master gage. The

necessary allowance must be made for the error in the master. A tolerance of plus or minus 0.0002 inch (0.005 millimeter) is allowed on the

distance between the gaging notch and the small end of the reference plug gage, or on the thickness of the reference ring gage. Note.—It is possible for reference plug and ring gages which come within all of the above tolerances

to vary from being flush with each other at the small end, or at the gaging notch, when screwed together

tight by hand. The maximum variation which might occur, expressed in terms of distance, is given in Column 4, and gages which come within these limits should be checked by measurement before being

rejected.12071°—21 5
66 NATIONAL SCREW THREAD COMMISSION

Inspection Gages.—The tolerance on inspection gages will be the same as on reference

gages. (See Table 26.) New Working Gages.—Column 5 of Table 27 gives the maximum allowable cumulation of all errors in the thread surface of new working gages, expressed in terms of diameter, and is also illustrated in Fig. 37. No point in the thread surface of the gage should be outside of the zone of tolerance indicated by the shaded portion of the

illustration. Note.—This column is used when checking gages by measurement. Column 6 gives the equivalent of Column 5, expressed in terms of distance parallel

to the axis, and represents the maximum distance which a new working ring gage

of perfect thickness or a new working plug gage of perfect length from small end to gaging notch may vary from being flush at the gaging notch, or at the small end,when

referred to basic dimensions. It is equal to 16 times Column 5, owing to the basic taper of 1 in 16, measured on the diameter.

Note.—This column is used when checking working gages by comparison with a gage the error of which

is known. The necessary allowance must be made for this error. Column 7 gives the equivalent of Column 6, expressed in terms of the decimal

part of a turn from basic dimensions.

Note.—This column is also used when checking working gages by comparison with a gage the error of which is known. The necessary allowance must be made for this error. A tolerance of plus or minus 0.0005 inch (0.0127 mm) is allowed on the distance between the gaging notch and the small end of the working plug gage, or on the thickness of the working ring gage. Note.—It is possible for working plug and ring gages which come within all of the above tolerances to vary from being flush with each other at the small end or at the gaging notch, when screwed together tight by hand. The maximum variation which might occur, expressed in terms of distance, is given in Column

8, and gages which come within these limits should be checked by comparison with reference gages before being rejected. It is also possible for working plug and ring gages which come within all of the above tolerances to vary

from being flush at the small end or at the gaging notch, when screwed tight by hand on a reference gage which comes within the tolerances specified for references gages. The maximum variation which might

occur, expressed in terms of distance, is given in Column 9, and gages which come within these limits should be checked by measurement before being rejected. Worn Working Gages.—The maximum wear on working gages must not be more

than the equivalent of one-half turn from the basic dimensions. In order that no work passed by the working gage shall be rejected by the inspection

gage, it will be necessary to discontinue the use of the working gage when it has worn

one-half turn. That is, the working gage should always be kept within the tolerance

of one-half turn from the basic dimensions.

Manufacturing Tolerance

The maximum allowable variation in the commercial product is one turn plus or one turn minus from the gaging notch when using working gages. (See Figs. 29, 30,

32, and 33.) This is equivalent to a maximum allowable variation of one and onehalf turns from the basic dimensions, owing to the allowance of one-half turn on working gages. National (American) Taper Pipe Threads

Taper external and internal threads are recommended for threaded joints for any

service.
PROGRESS REPORT 6 7

National Straight Pipe; Threads

Internal (Female).—Straight threaded internal wrought-iron or wrought-steel

couplings of the weight known as "standard" may be used with taper threaded pipe

for ordinary pressures, as they are sufficiently ductile to adjust themselves to the

taper external thread when properly screwed together. For dimensions see Table 20. For high pressures, only taper external and internal threads should be used.

External (Male).—Straight external threads are recognized only for special appli- cations such as long screws, tank nipples.

Long Screws

Long screws are used to a limited extent. This joint is not considered satisfactory

when subjected to temperature or pressure. In this application (see Fig. 35) the coupling has a straight thread and must make a joint with a National (American) Taper

Pipe Thread. In gaging, the National (American) Taper Working Plug Gage is used, allowing the same tolerance from the notch as for a taper thread. (See Fig. 34.) The straight thread on the pipe enters the coupling freely by hand, the joint being made by a

packing material between the locknut and the coupling. (See Fig. 35.) It is necessary that 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. Owing to the long engagement of thread, imperfections in pitch affect the fit when

the coupling is screwed on the pipe its full length. Refinements of manufacture and

gaging to insure a properly interchangeable product are more costly than the commercial use warrants; therefore, the use of this type of joint is not recommended.

Locknut Threads

Occasional requirements make it advisable to have a straight thread of the largest diameter it is possible to cut on a pipe. This has been standardized and is known as Maximum External and Minimum Internal Locknut Threads. For dimensions, see Table 21. The "tank nipple" shown in Fig. 36 is an example of this thread. In this application a National (American) Standard Taper Thread is cut on the end of the pipe

after having first cut the External Locknut Thread.

Symbols

The list of symbols given in Section II-3, together with additional symbols given

below, should be used in formulas for expressing relation of pipe threads and for use on drawings, etc. j4=pitch diameter of thread at end of pipe.

2J=pitch diameter of thread at gaging notch. C^maximum pitch diameter external locknut thread. C2=minimum pitch diameter internal locknut thread. L1 =distance from gaging notch to end of pipe=normal engagement by hand. L2=length of effective thread. D=nominal outside diameter of pipe=major diameter of pipe thread at L2 from

end of pipe. <2=internal diameter of pipe.
NATIONAL SCREW THREAD COMMISSION

Fig. 22.

Form of national taper pipe thread
PROGRESS REPORT 69

Figs. 23, 24, and 25.

Reference gagesfor checking working gages

fhq. 26. AT aMAU- FIG. 27:

Figs. 26 and 27.

Working gages for checking product

y
7o NATIONAL SCREW THREAD COMMISSION

NATIONAL TAPER

WORKING 'RINC. GA Ct B

FIG.28.

EXTERNAL TH REfii O

"TO G^Gf*

ONE TURN PLUS ONE TURN MINUS

FIC.S3. FIG.30.

EATERNflLTHI?SflD EXTERNAL. TH(?EflO

M/»XI/VIi"vl SIZE MINIMUM SIZE

FLUSH NATIONAL TAPE.R WORKING PLUG. GAG£ ONE TURN PLUS ONE TURN MINUS

FIG.3I. FIG.32. FIG.33.

INTEI?NflUTHI7£/IO INT£I?NAUTHR£A0 INTERNAL THREAD

"ro 6fl6E* fvi/Qx/mfni size iyhnim*/*? size

Figs. 28, 29, 30, 31, 32, and 33.

Gages for national taper pipe threads
PROGRESS REPORT 71

OA G/rtGCHAMFERED COUPLING. BOTTOM OFCHAMFER

^

~Fl USHATGr/IG//i6H07C/1

NATION A L 5TANDARP TAPER WORKING PUJQ<JflOE

. NAT IONAL STTANPAKP ffTR.AtQKT THREAD

Fig. 34.lustration of straight threaded coupling gaged with standard taper working

plug gage

(See Figs. 32 and 33 for tolerance. Taper four times actual)

Fig. 35.

Illustration of " long screw" joint between straight threaded coupling and taper

threaded pipe
72 NATIONAL, SCREW THREAD COMMISSION

Fig. 36.

Illustration of " tank nipple" thread

TAPEff UN 16. MEASURED ON DIAMETER

AXIS

A0

I I I A

Basic pitch diameter at small end of gage

B=Minimum pitch diameter at small end of gage

C=Maximum pitch diameter at small end of gage

(Column 1 from Table 26 for reference gages

IColumn 5 from Table 27 for new working gages

[Column 1 from Table 26 for reference gages

IColumn 5 from Table 27 for new working gages

No point on the thread surface of the gage should be outside of the zone of toler- • ance indicated by the shaded portion of the illustration The dotted line indicates the outline of. a perfect gage made exactly to the basic dimensions

Fig. 37.Illustration of tolerance and basic dimensions of a perfect taper pipe thread gage
PROGRESS REPORT 73

A=D-(0.05D) + 1.1)P

B=A+0.062 5U

L2 =P (0.8D+6.8)

Depth of thread=0.8P

Fig. 38.

National taper pipe thread notation
NATIONAL SCREW THREAD COMMISSION

a

Per

254

mm

270 180 180 140 140 2223 s sssss

1

00 00 CO 00 00 0OOO0O0O0O CO CO CO CO OO CO CO CO CO 00

thread g g§§ss 2.540 2.540 2.540 2.540 2.540 lllll

NNNNN NtsicviN^ NNNoiN

2.540 2.540 2.540

oaa.o •silill ill lllil IIIII IIIII lllll HI

mm

10.287 13.716 17.145 21.336 26.670 = 2^11

SSSSS

88.900

101.600 114.300 127.

000

141.300 ssSSl sssll sills Is!

issss mm mm m

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 ssssg gglli §§§§§

--"-2 d^SSS SSSSS

26.000 28.000 30.

000

•J

mm

4.572 5.080 6.096 8.128 8.611 10.

160

10.

668

10.

668

11.074 17.323 19.456 20.853 21.438 22.225 23.800 lllls sssss SISSS

sssss stssqjs sssss

63.

500

66.

675

69.850

Inches

0.180 .200 .240 .320 .339 ailSg slsss !§~ss ^^^^^ «<sj^rj^2.500 2.625 2.750

mm 6.

700

,

10.206 10.

358

13.

556

13.861 17.

343

17.953 18.377 19.215 28.

892

30.480 31.750 33.020 34.

290

35.

720 Sslss gills

SSSSS SSSSS sssss

sSI

SSS; min mis lllll lllll l§§ss sisls ssg

mm

9.519

12.443 15.926 19.

772

25.117 lg?2~ slgSS §§§13 Illli gsS

**m mm mm mm m

Inches

0.37476 .48989 .62701 .77843 .98886 1.

23863

1.58338 1.82234 2.29627 2.76216 3.38850 3.88881 4.38713 4.

88594

5.44929 6.

50597

7.

50234

8.

50003

9.

49797

10.

62094

11.61938 12.61781 13.87262 14.87419

15.

87575

16.87500 17.87500 19.87031 21.86562 23.86094

25.

85625

27.85156

29.

84687

mm

9.233

12.126 15.

545

19.264 24.579 30.

826

39.551 45.621 57.633 69.

076 SSiss ggsSS ssiSl sssss ess **m mm mm mm »

iiiii mil ---riri mil

«oci*TM

wmvo^o inn mm

S52~S 25.

70000

27.

68750

29.

67500

o

N

*s

"»°222

a

a S38S3 gg|2S §21as alls! sssss Igg

Nomina m >

' o&''<•'•'• « S« cvi n

: : : : : : : i i i iiiii

j i j QBO QQQOQ

: : : : :

• [666 66666

V^COolS «S°NN 26

O.D

28O.D30

O.D
PROGRESS REPORT 75

THIS THREAP IS C.AGEDWITH THE TAPER THREAPEP PL05 GAGE ANP SHOULD <S A GE

FU)5H,ATTHE FACE, WITH THE GAGING NOTCH ALL- tmUSt A MAXIMUM VARIA- TION OFONETURN PLUS OR MINUS FROM THE NOTCH

ba-sc pitch pia. fcR

straight pipe threap*

P\TCtt PIA. AT GAGING

N«TCH OF TAPER

FL.OG GAGE

SEE TABLE #£UL

FOR RELATION TO

TAPER. THREAP

Fig. 39.National straight pipe thread notation (internal)

0'

TABLE 20.—Dimensions of National Straight Pipe Threads

B Depth of thread Number of threads—

1 Inches mm Inch mm Per inch Per 254 mm

3 0.37476 9.519 0. 02963 0.753 27 270

6 .48989 12.443 . 04444 1.129 18 180 10 .62701 15.926 . 04444 1.129 18 180 13 . 77843 19.772 . 05714 1.451 14 140

19 .98886 25.117 .05714 1.451 14 140

25 1.23863 31.461 . 06956 1.767 ny2 115

32 1.58338 40.218 .06956 1.767 uy2 115 38 1.82234 46. 287 . 06956 1.767 uy2 115 50 2.29627 58.325 .06956 1.767 uy2 115 64 2. 76216 70. 159 . 10000 2.540 8 80

76 3. 38850 86. 068 . 10000 2.540 8 80

90 3.88881 98. 776 . 10000 2.540 8 80

100 4.38713 111.433 . 10000 2.540 8 80

113 4. 88594 124.103 . 10000 2.540 8 80

125 5. 44929 138.412 . 10000 2.540 8 80

150 6.50597 165. 252 . 10000 2.540 8 80

175 7. 50234 190.560 . 10000 2.540 8 80 200 8. 50003 215.901 . 10000 2.540 8 80 225 9. 49797 241.249 . 10000 2.540 8 80 250 10.62094 269. 772 . 10000 2.540 8 80

275 11.61938 295. 133 . 10000 2.540 8 80 300 12.61781 320. 493 . 10000 2.540 8 80 350 13.87262 352. 365 . 10000 2.540 8 80

375 14.87419 377. 805 . 10000 2.540 8 80

400 15.87575 403. 245 . 10000 2.540 8 80

425 16. 87500 428. 626 . 10000 2.540 8 80

450 17.87500 454. 026 . 10000 2.540 8 80

500 19. 87031 504. 707 . 10000 2.540 8 80 550 21.86562 555. 388 . 10000 2.540 8 80

600 23. 86094 606. 069 . 10000 2.540 8 80

650 25. 85625 656. 750 .10000 2.540 8 80

700 27.85156 707.431 . 10000 2.540 8 80

750 29.84687 ' 758. 112 . 10000 2.540 8 80

Nominal size

Inches a

H%

y2 m

11M

Hi

2

2Yi. 33^

44H

5

6

7

8

9

10

11

12

14 O. D..

15 O. T>._ 16 O.D..

17 O. D._ I8O.D..

20 O. D..

22 O. D..

24 O. D..

26 O. D..

28 O. D..

30 O. D..
7 6

B.PITCH DIA ATGAG/NG NOTCH C,= B4 (4PX06^5) ^T^4tjESr

OF NATIONAL TAPER PUK,G*<i£ Ce=B+ (SPXJ36eS) T^Af-EKTTrtKEAP

Fig. 40.

National locknut thread notation

TABLE 21.—Dimensions of National Locknut Threads

Nominal size Ci C, Depth of thread Number of threads—

Per 254 Inches mm Inches mm Inches mm Inch mm Per inch mm

Ys 3 38402 9. 754 38633 9 813 0.02963 0.753 27 270 M ----- 6 50378 12 796 50725 12 884 .04444 1.129 18 180 % 10 64090 16 279 64437 16 367 .04444 1.129 18 180 H 13 79628 20 225 80075 20 339 .05714 1.451 14 140 % 19 1 00672 25 571 1 01118 25 684 . 05714 1.451 14 140

1 25 1 26037 32 013 1 26580. 32 151 . 06956 1.767 Hi 115 Hi 32 1 60512 40 770 1 61055 40 908 .06956 1.767 iii 115 m 38 1 84407 46 839 1 84951 46 978 .06956 1.767 11* 115 2 50 2 31801 58 877 2 32344 59 015 .06956 1.767 11J 115

Ztt. 64 2 79341 70 953 2 80122 71 151 . 10000 2.540 8 80

3 76 3 41975 86 862 3 42756 87 060 .10000 2.540 8 80 3y2 90 3 92006 99 570 3 92787 99 768 . 10000 2.540 8 80 4 100 4 41838 112 227 4 42619 112 425 . 10000 2.540 8 80

113 4 91719 124 897 4 92500 125 095 . 10000 2.540 8 80

5 125 5 48054 139. 206 5 48836 139 405 . 10000 2.540 8 80

6 150 6 53722 166 046 6 54503 166 244 . 10000 2.540 8 80

7 175 7 53359 191 354 7 54141 191 552 . 10000 2.540 8 80

8 200 8 53128 216 695 8 53909 216 893 . 10000 2.540 8 80

9 225 9 52922 242 043 9 53703 242 241 . 10000 2.540 8 80

10 250 10 65219 270 566 10 66000 270 764 . 10000 2.540 8 80

11 275 11 65063 295 927 11 65844 296 125 . 10000 2.540 8 80

12 300 12 64906 321. 287 12 65688 321. 485 . 10000 2.540 8 80
PROGRESS REPORT 77

MM kg

0.364 .632 .845

1.268 1.687 2.506 3.394 4.064 5.473 8.660

Nominal weight per

it.

threaded and coupled Pounds

0.245 .425 .558 .852

1.134 1.684 2.281 2.731 3.678 5.819 sllsg Siifi ilssll

-«SJ3S ssssss

liii m

30.94 23.20 18.56 14.91 11.93 9.53 7.55 6.59 5.27 4.36 HHHHH

Length oi

pipe

per

sq.

ft.

of

external surface Feet

9.431 7.073 5.658 4.547 3.637 SS§§3

NC4 r4 iH

i

mm

3 46.45 80.

64

107.74 161.29 214.84 SSSSS SmSSoo

*m iiiii iiiii torn

I

la2 0.072 .125 .167 .250 .333 .494 .669 .799

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

iH

Trim

2 36.77 67.10

123.23 196.13 343.87 557.42 964.52

1313.55 2164.52 3089.04 4769.

69

6378.08 8212.92

10288.41 12907.

12

18639.39 24992.

31

33007.

16

32275.

55

40507.

17

52635.

58

52058.81 50874.

29

61311.73 74064.66 72965.

95

I

In»

0.057 .104 .191 .304 .533 .8641.495 2.036 3.355 4.788

81.585 80.691 78.

855

95.033

114.800 113.

097

thickness mm

1.727 2.235 2.311 2.769 2.870 3.378 3.556 3.683 3.912 5.156 5.486 5.740 6.020 6.274 6.553 7.112 7.645 7.036 8.179 8.687 7.087 7.798 9.271 9.525 8.382 9.525

«5

BO

diameter mm

10.287 13.716 17.

145

21.336 26.670 88.900

101.600 114.300 127.000 141.300 168.275 193.675 219.075 219.075 244.475 273.

050

273.050 273.

050

298.

450

323.851 323.

851

External Inches

0.405 .540 .675 .8401.050 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

Inside

diameter

•

mm

6.833 9.246

12.522 15.799 20.930 26.645 35.052 40.

894

52.

502

62.713 aSUSs Sslgs Skills

^13* sgsss sssgsg

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

il

size

Nomin; ijljjj

ixs is

VO c-^ CO oo o\
NATIONAL, SCREW THREAD COMMISSION

m

§g!SS2 S3£?$? SSSSS §8

»d «*«5^ SSSKS

Nominal weight per

ft.

plain

ends

Length of

pipe

per

sq.

meter

of

external surface m

30.94 23.20 18.56 14.92 11.93 9.53 7.55 6.59 5.27 4.36 3.58 3.13 2.78 2.50 2.25 1189 1.64 1.45 1.30 1.16 1.07 .98

Length of

pipe

per

sq.

ft.

of

ex- ^SSssS Iss§~ sslsi islsss

!

1

mm

3 60.00

101.29 140.00 206.45 279.

35

412.26 568.39 689.03 952.91

1454.20 1945.81 2372.91 2843.

23

3341.94 3943.23 5422.59 7220.66 8234.

21

9247.76

10387.76 11400.

67

12414.22

Inches

a

0.093 .157 .217 .320 .433 .639 .8811.068 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

I

mm

2 23.22 46.45 90.97

150.97 279.

35

463.

87

827.74

1140.00 1905.16 2734.

20

4261.30 5734.20 7417.43 9325.82

11738.09 16817.45 22240.04 29460.

06

37694.

27

48169.

12

58556.89 69957.55

issSs? ggggg lllss ssi-l

|° TM*

SSSSS g§

!

I

s 2glsS SSISs islss SIIII 11

. gcJeimmco r-icooodd d TM n co <-5 n n

^ISSSa Sslss IsssS stlis §1

3

d

!

1

ggssg Iiiii ass*! **m am m

s°§sl§ silEs ilsls ssis-g gg

•3d -

' 'rJ ^^^N^ m*-*V>lri iN»«d j-jjj

]

i

SSIIs ills! Sills sSsss 11

i-sss *m** mrn-m

»~m%z aSIIS llsls Ssssg gg

Jad •

- - - 'rtrtrtN N«n«« n»N»o; 03

1

1

—SSS 8885B SKSSS RS

. , . .

"xsfcsis: J3&i$ ^J&i JJJois
PROGRESS REPORT

Nominal weight

per

meter

plain

ends SSsKS §^gg a,TMTM^ doggo ajftggS

Ilia

Pounds

1.714 2.440 3.659 5.

214

6.408 9.029

13.695 18.583 22.850 27.541 32.530 38.552 53.

160

63.

079

72.424

Length of

pipe

per

sq.

meter

of

external surface m

14.92 11.93 9.53 7.55 6.59 5.27 4.36 3.58 3.

13

2.78 2.50 2.25 1.89 1.64 1.45

Length of

pipe

per

sq.

ft.

of

external surface Feet

4.547 3.637 2.904 2.

301

2.010

•

1.608 1.328 1.091 .954 .848 .763 .686 .576 .500 .442

!

Metal

mm

2 325.16 463.23 694.

19

989.

68

1713.55 2598.71 3526.46 4336.14 5226.46 6173.56 7316.14

10088.41 11970.99 13744.

54

sSsisi bIIss slSSI

Internal

mm

2 32.26 95.48 181.93" 406.45 612.90

1144.52 1589.68 2680.

65

3770.97 5034.

20

6494.21 8365.

18

12151.64 17489.71 23949.

72

i

B liggl S§IS§

l^«»s TMss sa'sas

i

i

mm

21.336 26.670 33.401 42.

164

48.260 60.325 73.025 88.900

101.600 114.300 127.000 141.300 168.275 193.

675

219.075

s!§3§§ issss

i

!

isasl Silas sll-s

j-SjWWSi S?SS§ gSS?S

S S5Sl§ igfgs £§§§§

Nominal

size 22SSS sssss

a
NATIONAL SCREW THREAD COMMISSION

11

JSSSSS 2 : : :

Ill

41 JIBS hh

*n pPfl mill

m

O T}- 00 Cs3 v£) ^-NOOOIO*

41 jlifif mill

so 311

S 41

511 lum mm

41 mm mm

Sl|

41

=11 mm

339.7 365.1 390.5 415.9 441.3 492.0 542.9

41 |sn ii i

i

si!

oi w h ui ! !

'. ; litisi MM

41 jjjj

imm mm

i!

1' |S!22S2 SSSSSg
PROGRESS REPORT 8

1

TABLE 26.—Tolerances for Reference Gages

Nominal size

1

(Total cumulative tol- erance on diameter. (See Fig. 37))

2

(Equivalent longitu- dinal variation (16 X Col. 1))

3

L. 4 Ul Vd — lent

aii£ uiai variation expressed

Q c don".

lllal pall

turn*

a4

Inches mm Inch mm Inch mm Inch mm

Vs 3 0. 00020 0. 0050 0. 0032 0.081 0. 086 0. 0068 0. 173 M 6 . 00022 .0056 .0035 .089 .063 .0074 .188

10 00024 0061 0038 . 097 .068 . 0080 . 203

y>&

13 .00026 !0066 !o042 .107 .059 .0088 .224

19 . 00028 .0071 .0045 .114 .063 .0094 .239

i 25 . 00030 .0076 .0048 .122 .055 .0100 .254 IX 32 . 00032 .0081 .0051 .130 . 059 .0106 .269 m 38 . 00034 .0086 .0054 .137 . 062 .0112 .284 50 . 00036 . 0091 . 0058 . 147 .067 .0120 .305 zy2 64 . 00038 .0097 .0061 .155 .050 .0126 .320

3 76 . 00038 .0097 .0061 .155 .050 .0126 .320 3M 90 .00041 0104 .0066 .168 .053 .0136 .345

4 100 . 00043 .0109 .0069 .175 .055 .0142 .361 4*2 113 . 00045 .0114 .0072 .183 .058 .0148 .376 5 125 . 00047 .0119 .0075 .191 .060 .0154 .391

6 150 . 00051 .0130 .0082 .208 . 065 .0168 .427 7 175 . 00055 .0140 .0088 .224 .070 .0180 .457

8 200 . 00059 .0150 .0094 .239 .075 .0192 .488 9 225 . 00063 .0160 .0101 .257 .080 .0206 .523 10 250 .00066 .0168 .0106 .269 . 085 .0216 .549

12 300 ! 00074 .0188 .0118 .300 .095 .0240 .610

14 350 . 00082 .0208 .0131 .333 .105 .0266 .676 16 400 . 00090 .0229 .0144 .366 .115 .0292 .742

18 450 . 00098 .0249 .0157 .399 .125 .0318 .808 20 500 .00106 .0269 .0170 .432 .135 .0344 .874 22 550 .00113 .0287 .0181 .460 .145 .0366 .930

24 600 .00121 .0307 .0194 .493 .155 .0392 .996 26 650 .00129 .0328 .0206 .523 .165 .0416 1.057

28 700 .00137 .0348 .0219 .556 .175 .0442 1.123

30 750 .00144 .0366 .0230 .584 .185 .0464 1.179

a Maximum amount it is possible for plug and ring gages to vary from being flush at small end or at gaging notch when screwed together tight by hand. (2 times Column 2 + 0.0004".) 12071°—21 6
82 NATIONAL, SCREW THREAD COMMISSION

TABLE 27.—Tolerances for Working Gages

Nominal size

5 Total cumulative tolerance on

diameter. (See

Fi?. 37)

6 Equivalent longi- tudinal variation. (16 times Column 5)

«7 68 c9

Inches mm Inch mm Inch mm Inch mm Inch mm

yi 3 0. 00040 0. 0102 0. 0064 0.163 0. 172 0. 0138 0. 351 0. 0103 0.262

>4 6 . 00044 .0112 .0070 .178 . 126 .0150 .381 .0112 .284

Pi 10 . 00048 .0122 .0077 .196 . 136 .0164 .417 .0122 .310

Yj 13 . 00052 . 0132 . 0083 . 211 . 118 . 0176 • 447 . jjj

19 . 00056 .0142 .0090 .229 . 126 .0190 .483 !0142 .361

1 25 . 00060 .0152 .0096 .244 . 110 .0202 .513 .0151 .384

32 . 00064 .0163 . 0102 .259 . 118 .0214 .544 .0160 .406 V4 38 . 00068 .0173 .0109 .277 . 124 .0228 .579 . 0170 .432

2..'. 50 . 00072 . 0183 . 0115 292 . 134 . 610 0180 tOt ZAT 64 . 00076 .0193 .0122 310 . 100 !0254 .645 !oi90 .483

3 76 . 00076 .0193 .0122 .310 . 100 .0254 .645 .0190 .483

90 . 00082 .0208 .0131 .333 . 105 .0272 .691 .0204 .518

4 100 . 00086 .0218 .0138 .351 . 110 .0286 .726 .0214 .544 4H 113 . 00090 .0229 .0144 .366 . 115 .0298 .757 .0223 .566 5 125 . 00094 . 0239 . 0150 . 381 . 120 . 0310 .787 . 0232 . 589

6 150 . 00102 .0260 .0163 .414 . 130 .0336 .853 .0252 .640

7..: 175 . 00110 .0330 .0176 .447 . 140 .0362 .919 .0271 .688

8... 200 . 00118 .0348 .0189 .480 . 150 .0388 .986 .0290 .737

9 225 . 00126 .0370 .0202 .513 . 160 .0414 1. 052 .0310 .787

10 250 . 00132 .0432 .0211 . 536 .170 .0432 1. 097 .0324 .823

12 300 . 00148 .0472 .0237 .602 .190 .0484 1. 229 .0362 .919

14 350 . 00164 .0513 .0262 .665 .210 .0534 1. 356 .0400 1. 016

16 400 . 00180 .0554 . 0288 .732 .230 .0586 1. 488 .0439. 1. 115

18 450 . 00196 .0594 .0314 .798 .250 .0638 1. 621 .0478 1. 214

20 500 . 00212 .0683 . 0339 .861 .270 .0688 1.748 .0516 1. 311

22 550 . 00226 .0719 .0362 .919 .290 .0364 1. 864 .0550 1.397

24 600 . 00242 .0759 .0387 .983 .310 .0784 1.991 .0588 1.494

26 650 . 00258 .0800 .0413 1.049 .330 .0836 2. 123 .0626 1.590

28 700 . 00274 .0841 .0438 1.113 .350 .0886 2. 250 .0664 1. 687

30 750 . 00288 .0732 .0461 1. 171 .370 .0932 2. 367 .0698 1.773

a Equivalent angular variation expressed as a decimal part of one turn. Maximum amount it is possible for new working plug and ring gages which come within the specified tolerances to vary from being flush at the small end or at the gaging notch when screwed together tight by

hand. (2 times Column 6+0.0010.)

c Maximum amount it is possible for new working plug or ring gages which come within specified toler- ances to vary from being flush at the small end or at the gaging notch when screwed on reference gage tight ... (Column 4+Column 8.)
PROGRESS REPORT 83

TABLE 28.—Corrections in Diameter for Errors in Angle

A=Error in half included angle of thread expressed in minutes

x. . 1.332P sin A

Correction in diameter = 1j^-z—T. sm (60+^4)

A 8 threads WV2 threads 14 threads IS threads 27 threads

Inch mm Inch mm Inch mm Inch mm Inch mm

0. 000056 0.0014 0. 000039 0.0010 0. 000032 0. 0008 0. 000025 0.0006 0.000017 0. 0004

. 000112 .0028 . 000078 . 0020 . 000064 . 0016 . 000050 .0013 . 000033 . 0008

. 000168 . 0043 . 000117 . 0030 OOOOQfi . 0024 00007^ 0019 nooo^o 0013

. 000224 . 0057 . 000156 . 0040 . 000128 . 0033 0000QQ . 0025 OOOOfifi 0017

5' . 000279 . 0071 . 000194 . 0049 0001 fiO . 0041 0001 74 . 0031 . 000083 UUUU03 . 0021

c/

. 000335 .0085 . 000233 .0059 . 000192 .0049 .000149 .0038 . 000099 .0025

7' . 000391 . 0099 . 000272 . 0069 . 000223 .0057 .000174 . 0044 . 000116 .0029

g/ . 000447 . 0114 . 0079 nnn?^ 0065 000199 0051 . nnm UUU LOL, 0034

9' . 000503 .0128 . 000350 . 0089 . 0073 • \J\J\JC1C1O . 0057 . 000149 0038

10' . 000558 . 0142 . 000388 . 0099 . 0081 . 0063 . 0042

.000614 .0156 . 000427 .0108 . 000351 .0089 .000273 .0069 . 000182 .0046

12' . 000670 . 0170 . 000466 . 0118 . 000383 .0097 . 000298 .0076 . 000198 .0050

1 Q' 0007?5 . 0184 000^0^ . 0128 . UUUTl J 0105 . nnn^?? \J\J\JOLiU 0082 nnn?i

0055

It ...... . 000781 '. 0198 . 000543 !oi38 . 000446 !0113 . 000347 !0088 . 000231 !0059

15' • UUUoo/ 0213 0148 . UUUt" / . UUUO

/

u . 0095 . UUU£*fo . 0063

. 000892 .0227 . 000621 .0158 .000510 .0130 . 000397 .0101 . 000264 .0067

17' . 000948 .0241 . 000660 .0168 . 000542 .0138 .000421 .0107 .000281 .0071

18' . 001004 .0255 . 000698 .0177 . 000574 .0146 . 000446 .0113 . 000297 .0075

19' . 001059 .0269 . 000737 .0187 . 000605 .0154 . 000471 .0120 .000314 .0080

20' .001115 .0283 . 000776 .0197 . 000637 .0162 . 000495 .0126 . 000330 .0084

21' .001170 .0297 . 000814 .0207 . 000669 .0170 . 000520 .0132 . 000347 .0088

22' . 001226 .0311 . 000853 .0217 . 000700 .0178 . 000545 .0138 . 000363 .0092

23' .001281 .0325 . 000891 .0226 . 000732 .0186 . 000570 .0145 . 000380 .0097

24' . 001337 .0340 . 000930 .0236 . 000764 .0194 . 000594 .0151 . 000396 .0101

25' . 001392 .0354 . 000969 .0246 . 000796 .0202 .000619 .0157 .000413 .0105

26' .001448 .0368 . 001007 .0256 . 000827 .0210 . 000643 .0163 . 000429 .0109

27' . 001503 .0382 . 001046 .0266 . 000859 .0218 . 000668 .0170 . 000445 .0113

28' . 001559 .0396 . 001084 .0275 . 000891 .0226 . 000693 .0176 . 000462 .0117

29' .001614 .0410 .001123 .0285 .000922 .0234 .000717 .0182 . 000478 .0121

30' .001669 .0424 .001161 .0295 .000954 .0242 . 000742 .0188 . 000495 .0126

45' . 002498 .0634 .001738 .0441 . 001427 .0362 .001110 .0282 . 000740 .0188

60' . 003322 .0844 .002311 .0587 .001899 .0482 . 001477 .0375 . 000984 .0250

TABLE 29.—Correction in Diameter For Errors in Lead

[Correction in Diameter= — 1.732 E. E=error in lead.]

Correction in diameter

lead

0. 00000 0. 00001 0. 00002 0. 00003 0. 00004 0. 00005 0. 00006 0. 00007 0. 00008 0. 00009

0. 00000 0. 00000 0. 00002 0. 00003 0. 00005 0. 00007 0. 00009 0. 00010 0.00012 0.00014 0. 00016

.00010 .00017 . 00019 . 00021 . 00023 . 00024 . 00026 . 00028 . 00029 . 00031 . 00033

. 00020 . 00035 . 00036 .00038 . 00040 . 00042 . 00043 . 00045 . 00047 . 00048 . 00050

. 00030 . 00052 . 00054 . 00055 . 00057 . 00059 . 00061 . 00062 . 00064 . 00066 . 00068

.00040 . 00069 . 00071 . 00073 . 00074 . 00076 . 00078 .00080 . 00081 . 00083 . 00085

. 00050 .'. 00087 . 00088 . 00090 . 00092 . 00094 . 00095 . 00097 .00099 . 00100 . 00102

. 00060 . 00104 .00106 .00107 . 00109 .00111 .00113 .00114 .00116 .00118 . 00120

. 00070 .00121 . 00123 .00125 .00126 .00128 .00130 . 00132 . 00133 . 00135 .00137

. 00080 .00139 .00140 .00142 .00144 .00145 .00147 .00149 .00151 .00152 .00154

. 00090 .00156 .00158 .00159 .00161 . 00163 .00165 .00166 .00168 . 00170 .00171

. 00100 .00173 .00175 . 00177 .00178 .00180 .00182 .00184 .00185 .00187 . 00189

.00110 .00191 .00192 . 00194 . 00196 . 00197 . 00199 .00201 . 00203 . 00204 . 00206

.00120 . 00208 .00210 .00211 .00213 . 00215 .00217 .00218 . 00220 .00222 .00223

.00130 .00225 . 00227 . 00229 . 00230 . 00232 .00234 . 00236 00237 .00239 . 00241 .00140 .00242 . 00244 .00246 . 00248 . 00249 .00251 . 00253 . 00255 . 00256 . 00258 .00150 .00260 .00262 . 00263 . 00265 . 00267 . 00268 . 00270 . 00272 .00274 . 00275

. 00160 . 00277 . 00279 . 00281 . 00282 . 00284 . 00286 . 00288 . 00289 . 00291 . 00293

. 00170 . 00294 . 00296 . 00298 . 00300 . 00301 . 00303 . 00305 . 00307 . 00308 .00310

.00180 . 00312 .00313 .00315 . 00317 . 00319 . 00340 . 00322 .00324 .00326 . 00327

.00190 . 00329 . 00331 . 00333 . 00334 . 00336 . 00338 . 00339 . 00341 . 00343 .00345

. 00200 . 00346 . 00348 . 00350 . 00352 .00353 . 00355 . 00357 . 00359 . 00360 . 00362
84 NATIONAL SCREW THREAD COMMISSION

VIII. FUTURE WORK OF COMMISSION

The problems of standardization so far considered by the commission have been those of most pressing importance to manufacturers and users of screw-thread products. Problems of less importance have necessarily been postponed until such time as they can be given proper consideration.

It is the intention of the commission, after issuing the present

tentative report, to continue the work of gathering information

in regard to special problems still to be considered. In this connection, there is outlined in the following paragraphs some of the

standardization work that should be done.

1. THREADS REQUIRING STANDARDIZATION

The following list includes the more important screw threads

which require standardization

:

(a) Threads cut on brass tubing.

(b) Instrument threads.

(c) Acme, square, buttress, and other special threads.

2. STANDARDIZATION OF PRODUCTS CLOSELY ALLIED TO THE MANUFACTURE OF SCREW THREADS

In addition to the standardization of various thread systems, it would be of great advantage to American manufacturers to have

established standards for stock tools and other appliances used in

the production of screw threads, such as are mentioned in the fol- lowing list:

(a) Taps.

(b) Dies.

(c) Sizes of bar stock for producing cut threads.

(d) Sizes of bar stock for producing rolled threads.

(e) Dimensions of bolt heads and nuts.

(/) Standardization of sheet-metal and wire-gage sizes.

(g) Standardization of tap-drill sizes.

3. POSSIBILITY OF INTERNATIONAL STANDARDIZATION

The recent war has demonstrated the need of interchangeability

of articles manufactured in this country with those manufactured

in foreign countries, and it is known that manufacturers and

authorities of Great Britain, France, and other foreign countries

are awake to the situation and, in fact, have already taken steps

toward the international standardization of screw threads and
PROGRESS REPORT 85

other manufactured articles. Furthermore, international standardization is of great importance in connection with the development of foreign trade.

In July, 1919, the commission sent to Europe a delegation of

its members 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 are anxious to

cooperate with the United States in this work. The time is very

opportune for accomplishments along this line, and it is the opinion of the commission that, as a result of the war, it should be possible to reach an agreement on an international standard thread.

Such an international standard should be established by giving

consideration to the predominating sizes and standards used in

manufactured products, as well as to the possibilities of providing

a means for producing this international screw thread by the use

of either the English or the metric system of measurement.

S. W. Stratton,

(Director, Bureau of Standards)

Chairman, National Screw Thread Commission.

Washington, June 26, 1920.
IX. APPENDIXES

APPENDIX 1. ORIGIN OF THE COMMISSION

(a) Historical.—The standardization of screw threads has been a subject of vital interest to manufacturers since the efforts of Sir Joseph Whitworth in 1841 and of William Sellers in 1864. The efforts of Sir Joseph Whitworth in ascertaining shop

practice in the manufacture of screw threads resulted in the standardization and adoption of the Whitworth Thread System, which found extensive use in England. When

William Sellers promulgated through the Franklin Institute the Sellers Thread,

which resulted in the extensive use of the present United States Standard series, a

great achievement of direct benefit to American manufacturers was realized. In recent years numerous organizations have carried forward the standardization of screw threads. The American Society of Mechanical Engineers, the Society of Auto- motive Engineers, the Bureau of Standards, and prominent manufacturers of special- ized thread products, have been the chief influences in standardization of screw threads

in this country. In England the standardization of screw threads has been carried forward by the British Engineering Standards Association, an organization formed in

1001. The development in the manufacture of machine tools, automobiles, agricultural

implements, typewriters, sewing machines, and other standard manufacturing pro- ducts has made apparent the need for standardized and interchangeable screw threads and threaded parts. In addition to the need of standardization, which grew by virtue

of improvements in general manufacturing practices, the difficulties encountered in the program for procuring munitions in the recent war demonstrated the vital necessity of standardized screw threads. Through the efforts 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.

(6) Commission Authorized by Congress.—As a result of this action, the National Screw Thread Commission was authorized by the following act of Congress, approved

July 18, 1918. (Public Document No. 201, 65th Cong., H. R. 10852.) 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 ofAmerica in Congress assembled, 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

commissioned officers of the Army, to be appointed by the Secretary of War; two commissioned officers 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. 86
PROGRESS REPORT 87

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

of its business. Sec. 6. That the commission shall cease and terminate at the end of six months from date the of its ap- pointment. Approved, July 18, 1918.

(c) LrFE of Commission Extended by Congress.—Prior to the expiration of the

original term of six months for which the commission was appointed, it became ap- parent that it would be impossible to complete in a satisfactory manner the work

outlined by the commission. An extension of time was therefore asked by the commission and granted by Congress in accordance with the following act: (Public No.

324, 65th Cong. H. R. 15495.) AN ACT To amend an Act to provide for the appointment of a commisson to standardize screw threads. Be it enacted by the Senate and House of Representatives of the United States ofAmerica in Congress assembled. That the Act providing for the appointment of a commission to standardize screw threads, approved July

eighteenth, nineteen hundred and eighteen, be, and the same is hereby, amended so that it will read: "That a commission is hereby created, to be known as the Commission for the Standardization of Screw

Threads, hereinafter referred to as the commission, which shall be composed of nine commissioners; one

of whom shall be the Director of the Bureau of Standards, who shall be chairman of the commission; two

representatives of the Army, to be appointed by the Secretary of War; two representatives of the Navy,

to be appointed by the Secretary of the Navy; and four to be appointed by the Secretary of Commerce, two of whom shall be chosen from nominations made by the American Society of Mechanical Engineers and two from nominations made by the Society of Automotive Engineers. "Sec. 2. That it shall be the duty of said commission to ascertain and e3tablish 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 Depart- ments, and, so far as pratcicable, 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. "Sec. 6. That the commission shall cease and terminate at the end of one year and six months from the date of its original appointment."

Approved, March 3, 1919.

(d) Life of Commission Again Extended by Congress.—Recognizing the impossibility of perfecting a report of this character in the first issue, and realizing the importance of providing an opportunity for making necessary changes, Congress

extended the life of the commission for an additional term of two years by the following

joint resolution: (Public Resolution, No. 34, 66th Cong. H. J. Res. 299.) JOINT RESOLUTION Extending the term of the National Screw Thread Commission for a period of two

years from March 21, 1920. Resolved by the Senate and House of Representatives of the United Stales of America in Congress assembled. That the term of the National Screw Thread Commission, created by an Act approved July iS, 1918, as amended by an Act approved March 3, 1919, be, and the same is hereby, extended for an additional period

of two years from March 21, 1920. Approved, March 23, 1920. APPENDIX 2. 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 organi- zation 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.
88 NATIONAL SCREW THREAD COMMISSION

(6) MEMBERS.—In accordance with the act, the following members were appointed.

Appointed by the Secretary of Commerce: Chairman

:

Dr. S. W. Stratton, Director of Bureau of Standards, Washington, D. C. On nomination by American Society of Mechanical Engineers: James Hartness.

F. O. Wells. On nomination by Society of Automotive Engineers: H. T. Herr.

E. H. Ehrman.

Appointed by the Secretary of War:

E. C. Peck, Lieut. Col. Ordnance, U. S. A.

O. B. Zimmerman, Major of Engineers, U. S. A. Appointed by the Secretary of the Navy:

E. J. Marquart, Commander, U. S. N., Bureau of Ordnance.

S. M. Robinson, Commander, U. S. N., Bureau of Steam Engineering.

(c) Officers.—The following officers were elected by the commission.

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, ist Lieut, of Engineers, U. S. A., assistant secretary. A. W. Coombs, stenographic reporter.

(d) Committees.—The commission resolved itself into the following subcommittees,

with authority to call to their aid one or more experts for counsel. These subcommittees were responsible for compiling and auditing data pertaining to the subject

of their committee and for compiling reports for presentation to the commission as a

whole, for the action of the commission.

F. O. Wells, chairman. Commander S. M. Robinson.

E- H. Ehrman.

H. W. Bearce, secretary. Lieut. Col. E. C. Peck, chairman. James Hartness. E. H. Ehrman.

H. L. Van Keuren, secretary.

IF. O. Wells, chairman.

J Commander E. J. Marquart.

Maj. O. B. Zimmerman.

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

Lieut. Col. E. C. Peck. Commander E- J- Marquart. H. L. Van Keuren, secretary.

I

James Hartness, chairman.

Lieut. Col. E. C. Peck.

F. O. Wells.

IE.

H. Ehrman, chairman.

Maj. O. B. Zimmerman.

Commander S. M. Robinson.

On May 23, 1919, Capt. John O. Johnson was appointed by the Secretary of War to succeed Maj. O. B. Zimmerman. On July 14, 1919, Commander N. H. Wright was appointed by the Secretary of the Navy to succeed Commander S. M. Robinson,

and on October 7, 1919, Commander L. M. McNair was appointed by the Secretary

of the Navy to succeed Commander E. J. Marquart. While the commission was in

Pitches, systems, andform of thread

Classification and toler- ances

Terminology <

.

Gages

test and methods of
PROGRESS REPORT 8 9

England and France, the Navy Department was represented by Capt. L. B. McBride.

On May 10, 1920, Commander Joseph S. Evans was appointed by the Secretary of the Navy to succeed Commander N. H. Wright. On December 15, 1920, Mr. Ralph E. Flanders was appointed by the Secretary of Commerce, to succeed Mr. James

Hartness. APPENDIX 3. PROCEDURE OF COMMISSION

(a) General Procedure.—In its work of establishing standards for screw threads

the commission has made particular effort to secure the actual facts concerning the need of standardization and the economic conditions to be provided for in the pro- duction and use of screw threads. The commission has had the advantage of being able to proceed rapidly inasmuch

as in recent years the accomplishments of the American Society of Mechanical Engineers and the Society of Automotive Engineers have paved the way toward the adoption

of necessary screw-thread standards. Without this preliminary work it would have

been considered impracticable and unnecessary. In addition the results accomplished by the British Engineering Standards Committee in their standardization work have been available to the commission and advantage has been taken of the accomplishments realized by this organization. Furthermore the commission has

availed itself of the opportunity to secure from such organizations as the Tap Makers

Association and representatives of prominent manufacturing concerns valuable

information and data regarding the production of tools and appliances for making

threaded products, as well as information and data regarding the application and use

of screw-thread products.

(6) Public Hearings.—After the preliminary organization of the commission

immediate steps were taken to secure from various screw-thread authorities and

representative manufacturers and users testimony as to the nature of the National

standards to be adopted for the use of the Government and for American manufacturers. To secure this information several public hearings were conducted in various industrial centers throughout the country.

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. Every effort was made to have in attendance at these hearings representatives of prominent manufacturers and organizations interested in standardization work. To this end invitations were

sent to a large mailing list and in addition announcement of the meetings, extending

invitations to be present, were published in the technical magazines. Topic sheets were distributed in advance of the hearings in order that witnesses 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 avail- able 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. The following schedule lists the dates of the various hearings:

October 7, igi8 Hearing held in Engineering Societies Building, 29 Vest Thirty-ninth Street, New York City. Topic—Fastening Screws, questions 1 to 5. October 21 Hearing held in Engineering Societies Building, 29 West Thirty-ninth Street, New York City. Topic—Pipe Threads, Brass Tubing, Hose Couplings, Special Threads and Instrument Threads

as outlined in Topic Sheet. November 8 Hearing held at Bureau of Standards, Washington, D. C. All topics, as outlined in Topic Sheet. November 11 and 12 Hearing held at Hotel Statler, Detroit, Mich. All topics, as outlined in Topic Sheet. November 13 Hearing held at Hotel Miami, Dayton, Ohio. All topics, as outlined in Topic Sheet.
go NATIONAL SCREW THREAD COMMISSION

(c) Topic Sheet.—The following topics are those which were discussed at the

various hearings

TOPICS FOR DISCUSSION AT HEARINGS OF NATIONAL SCREW THREAD

(z) Fastening Screws.—i. As a national standard, is there any objection to the continuation of the U. S. Standard System of thread diameters and pitches for general use in practically its present shape?

2. As a national standard, is there any objection to the adoption of the S. A. E. System of diameters and pitches of fine threads?

3. As a national standard, to what extent could the A. S. M. E. System of standard machine screws be adopted ? 4. There seems to be a general feeling that in the standardization of fastening screws tolerances and

clearances should be provided to cover several grades of work and to allow for several classes of fit ranging from a stud fit to a very loose fit. Would provision for four classes of fit including the stud fit be sufficient

for all grades of work encountered in screws made to the various systems previously mentioned or should such a classification include more than four classes?

5. Is there any objection to adopting the "standard hole" practice for screw threads; that is, the practice

of making all the taps for any particular thread of one basic size and securing the required fit by changing

the diameter of the screw or male threaded work which is to assemble with the nut cut by the basic tap?

(2) Pipe Threads.—1. As a national standard, is there any objection to the adoption of the American

Briggs pipe-thread sizes for both taper and straight pipe threads as accepted by the American Society of Mechanical Engineers?

2. In view of the experiments on the form of pipe threads conducted by the Pennsylvania Railroad in connection with the American Society of Testing Materials which tend to show the desirability of the U. S. Standard form with flat top and bottom one-eighth of the pitch, do you consider it advisable to adopt the U. S. Standard form instead of the present form which specifies a thread depth of 0.8 of the pitch with a resulting flat at the top and bottom of the thread which is quite small?

3. In your shop practice, to what extent do you employ gages for checking pipe threads and what do you consider a satisfactory tolerance for ordinary commercial work stated in turns either way from the

gaging notch?

(3) Brass Tubing.—1. What is your shop practice in connection with threads cut on various forms of brass tubing?

2. To what extent do you consider it possible to standardize the general practice on the threads used on

brass tubing?

(4) Hose Couplings.—1. As a national standard, is there any objection to the adoption of the hose cou- pling sizes now known as the National Standard hose couplings in the sizes from 2M inches to 4K inches as recommended by the National Fire Protection Association, Bureau of Standards, American Society of Mechanical Engineers, and other organizations?

2. What is your shop practice in the manufacture of hose coupling threads on sizes below 2M inch?

3. To what extent do you consider it possible to standardize commercial practice in the manufacture

of hose-coupling threads on the sizes below 2V3 inch?

(j) Acme and Other Special Threads.—1. What is your shop practice in the manufacture of Acme threads and other special threads used in machine construction?

2. To what extent do you consider it possible to standardize the form of thread and pitches used in the manufacture of Acme threads and to standardize other special threads used in machine construction?

3. To what extent do you consider it possible to standardize the general practice with reference to the diameters used for Acme thread pitches?

(6) Instrument Threads.—1. In your shop practice in the manufacture of instruments, to what extent do you use the A. S. M. E. threads; the British Association threads; metric threads; or your .own special threads, and to what extent do you consider it possible to standardize commercial practice for this class

of work?

(d) Attendance at Hearings.—The hearings of the commission were well at- tended by representatives of prominent manufacturers and by authorities on screw- thread subjects as is indicated in the following list of persons attending the various

hearings. This attendance was secured in spite of the fact that manufacturers were

extremely busy in connection with military preparations.

COMMISSION

[N. S. T. C. No. 7. National Screw Thread Commission, October 25, 1918]

HEARING AT NEW YORK CITY OCTOBER 7, 1918 Members and Officers of Commission Present—

Dr. S. W. Stratton, chairman. James Hartness. F. O. WeUs.

E. H. Ehrman.

Major O. B. Zimmerman.

H. L. Van Keuren, executive secretary. H. W. Bearce, general secretary.
PROGRESS REPORT 91

Men Representing Manufacturing Concerns Pres- int—

C. D. Terry, National Tube Co. George W. Thurston, American Screw Co. F. O. Lincoln, S. J. Besse, Morse Twist Drill &

Mach. Co. William H. Ure, Eastman Kodak Co., Camera

"Works. John C. Dense, Willys-Morrow Co.

J. E. Myers, P. R. R. Test Dept. Arthur A. Fuller, Watervliet Arsenal. Wilber C. Searle, Worcester Machine Screw Co. Charles C. Persiani, Clark Bros. Bolt Co. E. S. Sanderson, G. H. Wayne, Scovill Manufacturing Co.

Isaac F. Baker, General Electric Co. Luther D. Burlingame, Brown & Sharpe Manufacturing Co. A. H. Emery, Glenbrook, Conn. William B. Mcintosh, Coates Machine Tool Co. E. Burdsall, Russell, Burdsall & Ward Bolt & Nut

Co. Ralph E. Flanders, manager, Jones & Lamson

Machine Co. HEARING AT NEW YORK

Members and Officers of Commission Present—

Dr. S. W. Stratton, chairman. James Hartness. F. O. Wells. E. H. Ehrman.

Lieut. Col. E. C. Peck. Maj. O. B. Zimmerman.

H. L. Van Keuren, executive secretary. H. W. Bearce, general secretary. Men Representing Manufacturing Concerns

Present—

J. E. Myers, P. R. R. Test Dept.

C. M. Pond, Pratt & Whitney Co. D. W. Roberts, American Brass & Copper Co.

J. C. Meloon, General Fire Extinguisher Co. C. D. Terry, National Tube Co.

C. E. Skinner, Westinghouse Electric & Manufacturing Co. Thomas K. Bigg, Bridgeport Brass Co. F. M. Griswold, General Inspector, National Board

Fire Underwriters.

J. Q. Salisbury, National Cash Register Co. William H. Ure, Eastman Kodak Co.

I. F. Baker, General Electric Co. G. H. Woodroffe, Parkesburg Iron Co. George M. Bond, Hartford, Conn.

F. J. Cole, American Locomotive Works.

Erik Oberg, editor, "Machinery."

Charles Glover, H. H. Jones, The Corbin Screw

Corp. Ethan Viall, "American Machinist."

C. B. Buxton, American Locomotive Co. F. R. Stevens, American Locomotive Co.

J. L. Fitts, Warren Webster Co.

S. F. Newman, Landis Machine Co.

J. J. McBride, American Car & Foundry Co. W. J. Parsons, Millers Falls Co. W.Henry Martin, Arthur Knapp Engineering Corp.

Charles H. Jackmus, Ansonia Manufacturing Co. H. J. Bingham Powell, R. W. Sutherland, British War Mission. Frederick S. Thompson, Hartford Machine Screw

Co. F. J. Echols, Pratt & Whitney Co. Frank A. Turner, Becker Milling Machine Co. Will R. Porter, S. S. White Dental Manufacturing

Co. Werner O. Olson, Edison Phonograph Works.

A. H. Moore, General Electric Co. F. J. Cole, American Locomotive Works.

CITY OCTOBER 21, 1918. Frank A. Turner, Becker Milling Machine Co. Richard L. Wilcox, Waterbury Foundry & Machine Co. William Prellwitz, Ingersoll-Rand Co., A. S. Cameron Steam Pump Co. Frederick R. Banks, McNab & Harlin Manufacturing Co. William H. Burt, Waterbury Manufacturing Co. N. R. Butler, Worthington Pump & Mach. Corp. Edwin L. White, president J. H. White Manufacturing Co. G. B. Peckop, Malleable Iron Fitting Co.

C. W. Stephen, Pratt & Cady Co. Incorporated. B. H. Blood, Pratt & Whitney Co. Ethan Viall, managing editor ''American Machinist." William J. Baldwin, consulting engineer. World

Building, New York City. H. Koester, The Bristol Co. George R. Bott, The Norma Co. of America.

S. F. Newman, Landis Machine Co. H. J. Bingham Powell, British War Mission. A. M. Hauser, Crane Co. A. Bousfield, The Fairbanks Co. T. H. Blackmore, J. L. Mott Iron Works.

Joseph E. Stutz, Thomas Devlin Manufacturing Co. William Ferber, Keuffel & Esser Co. HEARING AT WASHINGTON, D. C, NOVEMBER 8, 1918.* Members and Officers of Commission Present.—

Dr. S. W. Stratton, chairman. James Hartness. F. O. Wells. E. H. Ehrman.

Lieut. Col. E. C. Peck. Maj. O. B. Zimmerman. Commander S. M. Robinson. Commander E. J. Marquart. H. L- Van Keuren, executive secretary. H. W. Bearce, general secretary. "Lieut. Robert Lacy, assistant secretary. *Mr. J. B. Thomas, designated by Mr. H.

sequent sessions of the Commission.

Men Representing Government Departments Present.—

E. C. Gillette, Bureau of Lighthouses. R. H. Shappell, Bureau of Engraving and Printing. Horace K. West, Walworth Manufacturing Co. H. W. GrofT, Frankford- Arsenal.

Lieut. A. N. Van Nostrand, Signal Corps, Elec. Eng. Section. H. H. Farr, Machinery and Small Arms Section. Capt. F. R. Mead, Gage Section, Insp. Division. Capt. Bordinat, Trench Warfare Section. F. H. Walsh, Bureau of Construction and Repair. Herr as his representative, attended this and sub-
92 NATIONAL SCREW THREAD COMMISSION

K. D. Williams, Bureau of Steam Engineering. Maj. H. B. Pratt, U. S. Marine Corps. W. E. Krotee, Inst. Section, Ordnance Office.

J. S. Wiley, Ord. Eng. Equipment Section. F. A. Hunnewell, constructor, U. S. Coast Guard.

Ensign A. J. Mummert, U.S.N. R. F., Bureau of Steam Engineering. Commander S. M. Henry, Bureau of Construction and Repair. E. G. Fischer, U. S. Coast and Geodetic Survey.

Archibald Black, Spec. Section, Aircraft Division. Ensign D. W. Kent, U. S. N. R. F., Bureau of Steam

Engineering. Lucian C. Jackson, Engine Production Section. Admiral George A. Burd, care of Commandant,

Navy Yard, New York City. D. A. Gurney, Mobile Gun Carriage Section. Lieut. Cause, Gage Section, Army Ordnance Dept.

Capt. Q. B. Newman, U. S. Coast Guard.

J. B. Thomas, Westinghouse Elec. & Mfg. Co. HEARING AT DETROIT, MICH., NOVEMBER 11, 1918 Members and Officers of Commission Present.—

Dr. S. W. Stratton, chairman. James Hartness. F. O. Wells. E. H. Ehrman.

Lieut. Col. E. C. Peck. Maj. O. B. Zimmerman.

H. L. Van Keuren, executive secretary. H. W. Bearce, general secretary. Lieut. Robert Lacy, assistant secretary. Men Representing Manufacturing Concerns Present.—

W. J. Pasinski, Burroughs Adding Machine Co. W. H. Urquhart, Curtis F. Smith, Michigan Bolt and Nut Works.

C. C. Bartlett, Crane Co. R. W. Davis, Mitchell Motors Co. Robert P. Smith, Packard Motor Car Co. Paul H. McCain, Pheoll Manufacturing Co.

D. A. Wallace, Western Electric Co.

F. A. Whitten, General Motors Truck Co. Charles Olsen, Continental Motor Manufacturing

Co. Mr. Cedarstrom, Morgan & Wright. B. N. Ackles, T. R. Rayl Co.

J. B. Thomas, Westinghouse Elec. & Mfg. Co. George E. Goddard, Dodge Bros.

C. A. Knill, C. H. Besly & Co. W. C. Yeatman, Chicago Nut Co.

C. C. Rhode, Champion Spark Plug Co. H. I. Woolsen, mechanical engineer, The Stude- baker Corp.

E. Mauren, Solvay Process Co. Ernest T. Bysshe, Bureau of Aircraft Production. A. E. Buelow, Lamson & Sessions Co. T. McLaughlin, Roe Stephens Manufacturing Co. H. S. Huncke, Detroit manager, Greenfield Tap&

Die Corp. HEARING AT DAYTON, OHIO, NOVEMBER 13, 1918.

Members and Officers of Commission Present—

James Hartness, vice chairman.

F. O. Wells. E. H. Ehrman.

Lieut. Col. E. C. Peck. Major O. B. Zimmerman. Commander E.J. Marquart. H. L. Van Keuren, executive secretary. H. W. Bearce, general secretary. Lieut. Robert Lacy, assistant secretary. Men Representing Manufacturing Concerns Present—

A. S. Hendricks, W. H. McCarthy, Computing

Scale Co. George A. Decker, S. Lawson, Warner & Swasey Co.

H. Ritter, Lukenheimer Manufacturing Co. R. V. Hutchinson, Dayton-Wright Aeroplane Co. L. C. Jackson, Engine Production Section. William F. Hoffman, superintendent, Robbins &

Myers Co. Frank L. Walker, Z. C. Bradford, Dayton Engineering Laboratory. A. I. Fischer, National Association of Brass Manufacturers. M. T. Byrne, Davis Sewing Machine Co.

J. F. Harrison, Atlas Bolt and Screw Co.

C. E. Watterson, Sheffield Machine and Tool Co.

J. B. Johnson, Bureau of Aircraft Production. Ernest T. Bysshe, Bureau of Aircraft Production,

Section of Gages and Standards.

J. B. Thomas, Westinghouse Elec. & Mfg. Co.

(e) Persons Attending Meetings of the Commission.—In addition to the evidence secured at the various hearings, there were several instances where special

representatives or authorities on screw-thread subjects were called for conference with the commission during its meeting at Washington. In this connection, the

following persons were in attendance at one of the meetings of the commission

Herbert Chase, representing the Society of Automotive Engineers. H. J. Bingham Powell, representing the British Ministry of Munitions.

C. A. Powell, representing the British Ministry of Munitions.

Representative J. Q. Tilson.

J. E. Ducard, representing the French High Commission.

F. G. Echols, representing the Tap Makers Association.

(/) Experiments.—A large number of experiments and tests were made by the Bureau of Standards to verify the results obtained by the consideration of the data

collected at the various hearings and also in connection with the development of
PROGRESS REPORT 93

tolerances and other technical subjects considered by the commission. In addition

to the experiments conducted by the Bureau of Standards, several of the members

of the commission conducted experiments and research work at their own expense.

(g) Meetings of the Commission.—Meetings of the commission were called for the purpose of outlining and formulating the procedure and for considering the infor- mation collected at the various hearings and for the formulation of the progress report

of the commission. The meetings held were as listed in the following schedule: September 12 and 15, iqi8.—preHminary informal meeting for the purpose of considering the organization and outlining of a program.

September 2j and 24, iqi8.—Completing program and formulating topics for hearings.

November 21 and 22, igi8.—Meeting of subcommittees and commission for outlining

and formulating progress report. December 20 and 21, igi8.—Meeting of the commission for considering the possibilities of an international standard of screw thread ; extension of time of commission ; and per- fecting the progress report. December 28, igi8.—Meeting of subcommittee on Terminology.

January 6, igig-—Meeting of subcommittee on Classification and Tolerance, Hotel Winton, Cleveland, Ohio. January 7, igig.—Meeting of subcommittee on Pitches, Thread Systems, and

Form of Thread, Hotel Statler, Buffalo, N. Y.

January 20 to 24, igig.—Meeting of commission for perfecting the progress report. February IJ to ig, igig.—Meeting of commission for consideration of tentative report. March 24 and 25, igig.—Meeting of commission for further consideration of tentative

report. April 7 to g, igig.—Meeting of subcommittee on Classification and Tolerances,

Cleveland, Ohio. April 14 to 16, igig.—Meeting of subcommittee on Classification and Tolerances,

Cleveland, Ohio. April 28 and 2g, igig.—Meeting of commission for further consideration of tentative

report. May 26 and 2J, igig.—Meeting of commission for further consideration of tentative

report. July 28 to 30, and August 8, igig.—Meetings with British Engineering Standards

Association, London, England.

August 11 and 14, igig-—Meetings with Societe d ' Encouragement pour l'lndustrie Nationale, Paris, France. September 15, igig.—Meeting of commission to hear report of European conferences.

October 6, igig.—Meeting of commission in New York City to consider report of manufacturers and users of screw-thread products with reference to tentative report. November 24 and 25, igig.—Meeting of commission in Cleveland, Ohio, to consider

final form of tentative report. APPENDIX 4. HISTOPJCAL

(a) General.—The initial accomplishments 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 X in. to 6 ins., inclusive. The threads had an included angle of 6o° and a

fiat surface at the crest and root equal to one-eighth of the pitch . This systemls known

and used at the present time as the Franklin Institute Thread, the Sellers Thread,

and commonly as the United States Thread.
94 NATIONAL SCREW THREAD COMMISSION

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 stand- ard threads by American railroads for the development of their lines and equipment.

While the United States Standard Thread System fulfilled a great need in the devel- opment of our great railway systems, it did not fully meet the requirements of the auto- mobile, machine-tool, instrument, and light-machinery industries. The requirements

of these industries made apparent the need of additional standard threads and to fulfill these needs a thread system having finer pitches than the United States Standard System was recommended by the Society of Automotive Engineers; and a machinescrew thread series which provided smaller size screws than the United States Stand- ard Threads was recommended by the American Society of Mechanical Engineers.

The progress of machine design and manufacture has established an extensive use of these fine thread series. Previous to the war, America led in many lines of quantity production. The war

has brought about a great extension in quantity production in other countries. One

of the prerequisites of quantity production is standardization of form and dimensions

of parts, in order that interchangeability may be established. This is especially important in the matter of screw-thread parts since there are two mating parts that must

fit and these parts in many cases are made in different places. Standardization is important to both the manufacturer and the user of a machine, as the user should be

able to buy locally a screw or nut for replacement in case of breakage or wear.

(6) Bibliography.—A very complete bibliography of screw-thread literature has been prepared by Henry E. Haferkorn, librarian Engineer School Library, Washington Barracks, D. C, and published as Supplement 2, Professional Memoirs, No- vember-December, 1918, Volume X, No. 54. APPENDIX 5. TECHNICAL

(a) Screw-Thread Fits.—With reference to the classification of screw-thread fits, attention is called to the fact that the minimum threaded hole or nut corresponds to the basic size; that is, the pitch diameter of the minimum nut is basic for all classes of fit. This condition permits the use of taps which when new are oversize and which

are discarded when the hole cut is at the basic size. In order to secure the desired fit the screw size is varied ; the maximum screw cor- responds to the basic size for the Medium-Fit Class, is slightly above basic size for Close-Fit Class, considerably above the basic size in the Wrench-Fit Class, and below

the basic size for the Loose-Fit Class.

(b) Application of Tolerances on Screw Thread Product.—The tolerances

specified in Column 7 of Tables 5, 10, 13, and 16, Section V, are the net tolerances which are in no way reduced by permissible manufacturing tolerances provided for master gages. These master-gage tolerances are provided for by being added to the net tolerances. Thus the extreme or drawing tolerances are the net working toler- ances increased by the master-gage increment or equivalent diametrical space

required to provide for the master-gage tolerances. The limits established for the extreme tolerances should in no case be exceeded. The application of gage toler- ances in relation to tolerances allowed on the work can be best understood by considering that the extreme tolerances represent the absolute limits over which variations

of the work must not pass. The manufacturing tolerances required for limit master

gages are then deducted from the extreme tolerances producing the figures specified as net tolerances. Further reduction of the extreme tolerances is caused by the manufacturing tolerances required for the inspection gages and working gages.

It is essential that the proportion of the tolerance used by the workmen producing

the work at the machine be well within the net tolerance limits. The net tolerance

limits as established by the master gages may be considered as the largest circle of the target, the space occupied by the master-gage tolerances representing the width
PROGRESS REPORT 95

of the line establishing the largest circle. The marksman always aims to hit the

bull's-eye. Any mark inside of the largest circle or cutting the circle scores. Any

mark outside of the largest circle does not score. The same is true in producing

work: The careful manufacturer will aim to produce work which is in the center of tolerance limits. The bull's-eye in this case, which is the working tolerance used

at the machine, will be considerably less than the net tolerance and the result will be that a very large percentage of the work will be accepted, and spoiled or rejected

work will be reduced to practically nothing. If the net tolerance limits are used as working limits at the machine, there will be a larger percentage of rejections due to differences in gages and wear of both tools and gages. The application of this principle is illustrated in Fig. 41. ^
96 NATIONAL SCREW THREAD COMMISSION

(c) Disposition of Gage Tolerances.—Fig. 41 is a diagram which shows the

relative position of master-gage, inspection-gage, and working-gage tolerances with

reference to the net tolerance allowed on the work.

(1) Extreme Working Limits.—The extreme limits as shown by the lines A and a in

Fig. 41 represent the absolute limits within which all variations of the work must be

kept, including permissible variations provided for manufacturing tolerances on

master gages. The manufacturer of the product should not be concerned with the extreme tolerances, but should work within the net tolerance limits. The extreme

tolerance limits are included for the manufacturer or inspector of master gages, and,

in no case, should master gages be approved which are outside of the dimensions

established by these extreme limits.

(2) Net Working Tolerance Limits.—The lines at b and B represent the net working

tolerance limits within which all manufactured product must come.

(j) Master-Gage Tolerances.—The regions A B andafr represent the space required

to provide for the "Go" and "Not Go" master-gage tolerances, respectively.

(4) Master Gages Represent Net Tolerance Limits.—Master gages provide physical standards representing the limits placed on the work. The master-gage tolerances

are placed within the extreme tolerance limits. However, the manufacturer receives the full benefit of the specified net tolerance. So far as the manufacturer is con- cerned, he should, in no case, permit variations in the work produced to extend beyond the limits established by his master gages.

(5) Inspection Gage Tolerances.—The regions BC and be represent the space required to provide for the "Go" and "Not Go" inspection-gage tolerances, respectively. The inspection-gage tolerances are placed inside the net tolerance limits.

(<5) Working-Gage Tolerances.—The regions DC and dc represent the space required

to provide for the " Go " and "Not Go ' ' working-gage tolerances, respectively. These

working-gage tolerances are placed within the net tolerance limits. This insures that any work accepted by the working gage will be accepted by the inspection gage, and that work accepted by both working gage and inspection gage will be within the net tolerance limits.

(d) Wear on "Go" Gages.—The "Go" master gage is not to be used on the

product. It serves as a standard for comparative measurements or as a check for verifying the inspection or working gage. It also serves as a standard representing the wear limit for the inspection or working gage. The "Go" master gage is, therefore, not subject to wear. The "Go" inspection gage may wear until it reaches the size represented by the master gage. As shown in Fig. 41 the wear provided for the inspection gage is that which takes place within its own tolerance region. However, a definite allowance

for wear may be provided for the "Go" inspection gage in addition to its tolerance region if desired. The "Go" working gage wears within its own tolerance limits and through the

inspection-gage tolerance region and continues to properly accept work until worn

to the dimension established by the "Go" master gage. It is good practice to

transfer the "Go" working gage to use as an inspection gage when it is worn so that

its dimension corresponds to that of the inspection gage.

(e) Wear on "Not Go" Gages.—The "Not Go" master gage is not to be used on

the product. It serves as a standard for comparative measurements or as a check to verify the inspection or working gage. It is therefore not subject to wear. The "Not Go" inspection gage wears within its own tolerance region and into the

tolerance region established for the "Not Go" working gage. It is good practice to transfer the "Not Go" inspection gage to use as a working gage when it is worn so that its dimension corresponds to that of the "Not Go" working gage. The "Not Go" working gage wears within its own tolerance region into the working

tolerance. It is purely an economic question as to when the " Not Go ' ' working gage
PROGRESS REPORT 97

should be discarded due to wear, inasmuch as continued use reduces the working

tolerance, the result of which must be balanced against the cost of a new gage.

40 So 60 70 SO 90 tOO

4 S 6 7 3 9 to 3 40 50 SO 70 80 SO

Fig. 42.Illustration of relation between extreme tolerance and net tolerance

(/) Relation between Extreme Tolerance and Net Tolerance Shown

Graphically.—The relation between the extreme tolerance and the net tolerance

for Class III, Close Fit, is shown graphically in Fig. 42. The tolerances and allowances for Classes I, II-A, II-B, and III are shown in Tables

5, 10, 13, and 16, Section V. 12071°—21 7
98 NATIONAL SCREW THREAD COMMISSION

APPENDIX 6. GAGES AND METHODS OF TEST

The general subject of gaging screws is too extensive to be fully covered in this

report. Reference is made, however, to bulletins published by the Bureau of Standards covering various inspection methods, including the standard ring and plug

gages, and the optical projection method of gage inspection; also, to an article in the Journal of American Society of Mechanical Engineers of February, 1919, with ref- erence to the use of the projection lantern for gaging work. Inasmuch as the threaded-plug and ring limit gages are the most universally used scheme of gaging, and one that has been brought to the highest state of refinement, there is set forth herein what is considered the best practice used in the production

and use of such gages. It is understood, however, that it is not the intention of this commission to confine manufacturers to any particulary method of gaging, as that would tend to hinder progress.

It has been the practice of many manufacturers including Government shops, to work with "Go" gages only and to depend upon the judgment of good workmen to keep within proper limits by the amount of "shake" or difference between the work

and the gage. With a highly skilled and trained force working on but one kind of work and also referring the working gage to but one master gage, a fair degree of inter- changeability can be maintained under these conditions. In the recent military preparations, the Government required munitions in such

vast quantities and in such a short period of time that this method of insuring inter- changeability failed, and a method of gaging had to be established which did not

rely entirely upon the skill and judgment of the workmen or inspectors. One reason

for the necessity of a complete gaging system was that it was not possible to obtain a sufficient number of skilled workmen or inspectors. Furthermore, one master gage could not be used all over the country and consequently discrepancies in measure- ment between different shops had to be guarded against by the use of properly tested standards and by approved methods of measuring.

It is believed that the experience gained by manufacturers producing war material

will result in a much more extensive use of gages than was ever thought practicable

during prewar times The gage specifications which are given herein cover the manufacture, use, and application of a system of gaging which has been thoroughly demonstrated in the execution of war contracts as being adequate for the production

in large quantities of strictly interchangeable screw-thread product. It is not the

intention of this report to limit manufacturers to any particular methods of test in checking either the manufactured product or in measuring gages, for the reason that any specification which would tend to limit the development of new and improved

methods of measuring would be very undesirable. However, when the ordinary forms of thread gages are used, the specifications given herein will apply.

(a) Fundamentals.—The specifications for gages given herein are built upon the

following fundamental assumptions:

(1) Approved limit master gages do not reduce the net working tolerance.

(2) Permissible errors in angle of thread specified for "Go" gages tend to reduce the net working tolerance, while similar permissible errors on the "Not Go" gage tend

to increase the net working tolerance . These two factors, therefore, balance each other.

(3) Permissible lead errors specified for the "Go" gage reduce the net working

tolerance, while permissable lead errors on the "Not Go" gage tend to increase the net working tolerance.

(4) In order to realize the full net working tolerance, the permissible diametrical

variation specified for both " Go " and " Not Go ' ' gages (gage increment) is placed outside of the net tolerance limits. The extreme tolerance equals the net tolerance plus gage increment.
PROGRESS REPORT 99

(5) The "Go" gage should check simultaneously all elements of the thread (all diameters, lead, angle, etc.).

(6) The "Not Go" gage should check separately the elements of the thread.

(6) General Specifications. —The following general specifications refer in particular to gaging systems which have been found satisfactory by the Army and Navy

for the production of interchangeable parts as specified under the subject of "Classification and Tolerances. ' ' These specifications are included for the use of manufacturers where definite information is lacking. They are not to be considered mandatory

(1) Gage Classification. —Thread gages may be included in one of four classes, namely,

Standard Master Gages, Limit Master Gages, Inspection Gages, and Working Gages.

(2) Standard Master Gage.—The Standard Master Gage is a threaded plug represent- ing as exactly as possible all physical dimensions of the nominal or basic size of the threaded component. In order that the Standard Master Gage be authentic, the

deviations of this gage from the exact standard should be ascertained by the National Bureau of Standards and the gage should be used with knowledge of these deviations

or corrections.

(3) Limit Master Gages.—Limit Master Gages are for reference only. They repre- sent the extreme upper and lower tolerance limits allowed on the dimensions of the

part being produced . They are often of the same design as inspection gages. In many

cases, however, the design of the master gage is that of a check which can be used to verify the inspection or working gage.

(4) Inspection Gages.—Inspection Gages are for the use of the purchaser in accepting

the product. They are generally of the same design as the working gages and the dimensions are such that they represent nearly the net tolerance limits on the parts being produced. Inasmuch as a certain amount of wear must be provided on an in- spection gage, it can not represent the net tolerance limit until it is worn to master- gage size.

(5) Working Gages.—Working Gages are those used by the manufacturer to check

the parts produced as they are machined. It is recommended that the working gages be made to represent limits considerably inside of the net limits in order that suffi- cient wear will be provided for the working gages, and in order that the product

accepted by the working gages will be accepted by the inspection gages.

(6) Inspection and Working-Gage Sets for Screws.—The following list enumerates

the inspection and working gages required for producing strictly interchangeable

screws as specified for National Coarse Threads, National Fine Threads, or other

straight threads.

(i) A maximum or "Go" ring thread gage, preferably adjustable, having the re- quired pitch diameter and minor diameter. The major diameter may be cleared to

facilitate grinding and lapping.

(ii) A minimum or "Not Go" ring thread gage, preferably adjustable, to check

only the pitch diameter of the threaded work.

(Hi) A maximum or "Go" plain ring gage to check the major diameter of the threaded work.

(iv) A minimum or "Not Go" snap gage to check the major diameter of the threaded work.

(7) Inspection and Working-Gage Sets for Nuts.—The following list enumerates the

inspection and working gages required for producing strictly interchangeable nuts,

as specified for National Coarse Threads, National Fine Threads, or other straight threads.

(i) A minimum or "Go" thread plug gage of the required pitch diameter and major

diameter. The minor diameter of the thread plug gage may be cleared to facilitate grinding and lapping.

(ii) A maximum or "Not Go" thread plug gage to check only the pitch diameter of the threaded work.
lOO NATIONAL SCREW THREAD COMMISSION

(Hi) A "Go" plain plug gage to check the minor diameter of the threaded work.

(iv) A "Not Go '

' plain plug gage to check the minor diameter of the threaded work.

(8) Limit Master Gages Required for Checking Working or Inspection Gages Used on

Screw.—The following list enumerates the limit master gages required for the verification of the working or inspection gages as previously listed for verifying the screw.

(i) A set plug or-check for the maximum "Go" thread ring gage, having the same

dimensions as the largest permissible screw.

(it) A set plug or check for the minimum or "Not Go" thread ring gage having the same dimensions as the smallest permissible screw.

(Hi) A maximum plain plug for checking the minor diameter of both the "Go"

and "Not Go" inspection thread ring gage.

(9) Limit Master Gages Required for Checking Working or Inspection Gages Used on

Nut.—The following list enumerates the limit master gages required for the verifica- tion of the working or inspection gages as previously listed for verifying the nut.

(1) A minimum or "Go" threaded plug to be used as a reference for comparative measurements and corresponds to the basic dimension, or standard master gage.

(it) A maximum or

'

' Not Go ' ' threaded plug to be used as a reference for comparative measurements and corresponds to the largest permissible threaded hole.

(Hi) A minimum plain ring gage to check the major diameter of the " Go " and "Not Go '

' master threaded plug unless suitable measuring facilities are available for this purpose.

(10) Material.—Gages may be made of a good grade of machinery steel pack-hardened, or of straight carbon steel of not less than 1 per cent carbon; or preferably of an

oil-hardening steel of approximately 1.10 per cent carbon and 1.40 per cent chromium.

(it) Handles and Marking.—Handles should be made of a good grade of machinery

steel plainly marked to identify the gage.

(c) Design and Construction.—The following specifications will be helpful in the

design and construction of gages used for producing threaded work.

(j) Plain Plug Gages.—(i) Type.—All plain plug gages should be single-ended. Plain plug gages of 2 inches and less in diameter should be made with a plug inserted in the handle and fastened thereto by means of a pin. Plain plug gages of more than

2 inches in diameter should have the gaging blank so made as to be reversible. This can be accomplished by having a finished hole in the gage blank fitting a shouldered

projection on the end of the handle, the gage blank being held on with a nut. The "Go" plain plug gage should be noticeably longer than the "Not Go" plain

plug gage, or some distinguishing feature in the design of the handle should be used to serve as a ready means of identification, such as a chamfer on the handle of the " Go "

gage.

(2) Plain Ring Gages.—(i) Type.—Both the "Go" and "Not Go" gages should have

their outside diameters knurled if made circular. The " Go ' ' gage should have a decided chamfer in order to provide a ready means of identification for distinguishing the "Go" from the "Not Go" gage.

(3) Snap Gages.—(i) Type.—Snap gages may be either adjustable or nonadjustable.

It is recommended that all snap gages up to and including one-eighth inch be of the

built-up type. For larger snap gages, forge blanks, flat plate stock or other suitable construction may be used.

Sufficient clearance beyond the mouth of the gage should be provided to permit

the gaging of cylindrical work-

. Snap gages for measuring lengths and diameters may have one gaging dimension

only, or may have a maximum and minimum gaging dimension, both on one end, or maximum and minimum gaging dimension on opposite ends of the gage. When the maximum and minimum gaging dimensions are placed on opposite ends of the gage, the maximum or " Go " end of the snap gage will be distinguished from the minimum
PROGRESS REPORT IOI

or " Not Go " end by heaving the comers of the gage on the " Go " end decidedly chamfered.

(4) Plug Thread Gages—(z) Type.—All plug thread gages should be single-ended.

Thread plug gages 2 inches and less in diameter should be made with a plug inserted

in a handle and fastened thereto by means of a pin.

Plug gages of more than 2 inches in diameter, unless otherwise specified, should have the gaging blank so made as to be reversible. This can be accomplished by

having the finished hole in the gage blank fitting a shouldered projection on the end

of the handle, the gage blank being keyed on and held with a nut. "Not Go" thread plug gages should be noticeably shorter than the "Go" thread plug gages, in order to provide a ready means of identification, or the handle of the "Go" gage should be chamfered. End threads on plug thread gages should not be chamfered, but the first half turn

of the end thread should be flattened to avoid a feather edge.

(it) Dirt Grooves.—Inspection and working thread plug gages should be provided

with dirt grooves which extend into the gage for a depth of from one to four threads.

(Hi) Length of Thread.—The length of thread parallel to the axis of the gage should

for all standard "Go" thread plug gages, be at least as much as the quantity expressed

in the following formula:

Where L=length of thread D=basic major diameter of thread. For threaded work of shorter length of engagement than (1.5)0, the length of thread on the "Go" gage may be correspondingly shorter.

(5) "Not Go" Thread Gage for Pitch Diameter Only.—All "Not Go" thread plug

gages should be made to check the pitch diameter only. This necessitates removal

of the crest of the thread so that the dimension of the major diameter is never greater than that specified for the "Go" gage, and also removing the portion of the thread

at the root of the standard thread form. ( See Fig. 43.)

(6) Ring Thread Gages—(t) Type.—All ring thread gages should be made adjustable.

The "Go" gage should be distinguished from the "Not Go" gage by having a de- cided chamfer and both gages are to have their outside diameter knulred if made

circular. The end threads on ring thread gages should not be chamfered but the first half turn of the end thread should be flattened to avoid a feather edge.

(7) Length of Thread.—The length of thread parallel to the axis of the gage should,

for all standard "Go '

' ring thread gages, be at least as great as the quantity determined

in the following formula

:

L=(i. 5 )D

Where L=length of thread D— basic major diameter of thread. For threaded work of shorter length of engagement than (1.5)0, the length of thread on the "Go" gage may be correspondingly shorter.

(8) "Not Go" Ring Gage for Pitch Diameter Only.—"Not Go" ring thread gages should be made to check the pitch diameter only. This necessitates removal of the

crest of the thread so that the dimension of the minor diameter is never less than that

specified for the maximum or "Go" gage and also removing the portion of the thread

at the root of the standard form. (See Fig. 43.) (mi) Gage Tolerances.—There are specified herein for use in the production of National Coarse Threads, National Fine Threads, National Hose-Coupling Threads,

and for other straight threads, and for National Pipe Threads, several tables of gage manufacturing tolerances. Table 30 will be found practicable for all plain plug, ring, and snap gages used in connection with a measurement of screw-thread diameters. In addition to the
102 NATIONAL SCREW THREAD COMMISSION

NOTE.—"Not go " gages check pitch diameter only.

Minimum or Go Plug G/ige Maximum ovD/orGo FLugG/ise

Maximum or GoRing Gage Minimum o/f/Yot GoRingGage

Fig. 43.Illustration of "go" and "not go" plug and ring gages
PROGRESS REPORT 103

master-gage tolerances, suggested tolerances for inspection and working gages are

also given in Table 30. Table 3 1 will be found practicable for both, standard and limit master thread gages

for thread work designed in accordance with, the manufacturing tolerances for Class

I, Loose Fit, and Class II, Medium Fit, made to Tables 5, 10, and 13, Section V. Table 32 contains suggested manufacturing tolerances for inspection thread gages with a small allowance for wear for use in quantity production of Class I , Loose Fit, and Class II, Medium Fit thread work, made to Tables 5, 10, and 13, Section V. Table 33 contains suggested manufacturing tolerances for working thread gages with a small allowance for wear for use in quantity production of Class I, Loose Fit, and Class II, Medium Fit thread work, made to Tables 5, 10, and 13, Section V. Table 34 contains the tolerances suggested for both standard and limit master thread

gages for work designed in accordance with manufacturing tolerances for Class III, Close Fit thread work, made to Table 16, Section V. As the component tolerances for this class are relatively small, it is believed that the working gages will be required to be held within the gage tolerances shown in Table 34.

(e) Application of Gage; Tolerances.—(j) Tolerancesfor 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 Tables 31, 32, 33, and 34 should be

used. Attention is called to the fact that the tolerances on thread diameters vary in accordance with the number of threads per inch on the screw or nut being manufactured. 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 30 may be

used.

(2) Tolerances on Lead.—The tolerances on lead are specified as an allowable varia- tion between any two threads not farther apart than the length of thread engagement

as determined by the following formula:

(3) Tolerances on Angle of Thread.—The tolerances on angle of thread as specified herein 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 allowable on

angle of thread.

(4) Tolerances on Diameters.—The tolerances given for thread diameters in Tables

31, 32, 33, and 34 are applied in such a manner that the tolerances permitted on the

inspection and working gages occupy part of the extreme tolerance. This insures that

all work passed by the gages will be within the tolerance limits specified on the part drawing as represented by the limit master gages. The tolerances given also permit

the classification and selection of gages, so that if a gage is not suitable for a master gage

it may be classified and used as an inspection or working gage, provided that the errors do not pass outside of the net tolerance limits. The application of the tolerances on diameters of thread gages is exactly the same

as explained herein for plain gages. Example: Dimensions on component drawings.

Work to be gaged:

Hole 1. 250+0. 004=1. 254 max.

L=(i. S)D

where

L=length of thread engagement

D=basic major diameter of thread.

Shaft, I. 248+ . OOO' — . C04

— . ooo- 1. 250 min.

1. 248 max.

1. 244 min.
104 NATIONAL SCREW THREAD COMMISSION

Dimensions, Tolerances, and Limits for Gages

GAGES FOR HOLE

_

Type of gage

Limiting dimensions

of part

Gage

tolerances Gage limits

vi mil 171 trjiffPS * Limit master 1. 254 —

). 0000 1. 2540 .0003 1. 2537

Inspection 1. 254 .0004 1. 2536 .0007 1. 2533 Working 1. 254 . 0007 1. 2533

. 0011 1. 2529 Minimum gages: Limit master 1. 250 + .0000 1. 2500 + . 0003 1. 2503

1. 250 + . 0004 1. 2504 + .0007 1. 2507 Working 1. 250 + .0007 1. 2507 + .0011 1. 2511

GAGES FOR SHAFT

Maximum gages: Limit master 1. 248 — ). 0000 1. 2480

. 0003 1. 2477

Inspection 1. 248 . 0004 1. 2476

. 0007 1. 2473

1. 248 .0007 1. 2473

.0011 1. 2469 Minimum gages:

1. 244 + .0000 1. 2440 + .0003 1. 2443

1. 244 + .0004 1. 2444 + .0007 1. 2447 Working 1. 244 + .0007 1. 2447 + .0011 1. 2451

By comparison of the above figures, it will be seen that it is not possible for the

master, inspection, or working gage dimensions to overlap. This is further illustrated in Fig. 44. TABLE 30.—Manufacturing Tolerances on Plain Gages

Manufacturing

tolerance allowed on work

Allowable tolerance for master gages

Minimum

gage Maximumgage

Allowable tolerance for inspection gages

Minimum

gage Maximum

gage

Suggested tolerance for working gages

Minimum

gage Maximum

Up to 0. 0020

0.0021 to 0.0040....

0.0041 to 0.0060....

0.0061 to 0.0100....

0.0101 to 0.0200

0. 0201 to 0. 0500

+0.0000 + .0001 + .0000 + .0002 + .0000 + .0003 + .0000 + .0004 + .0000 + .0005

-0.0000

- .0001

.0000

.0002

.0000

.0006

.0000

.0003

.0000

.0004

.0000

.0005

.0000

.0006

+0.0001 + .0003 + .0002 + .0004 + .0004 + .0007 + .0006 + .0010

.0010

.0015 + .0020 + .0026

-0.0001

- .0003

.0002 .0004

.0004 .0007

.0006 .0010

.0010

.0015

.0020

.0026

+0. 0003 + .0005 + .0004 + .0007 + .0007 + .0011 + .0010 + .0015 + .0015 + .0021 + .0026 + .0033

-0.0003

- .0005

.0004

.0007

.0007

.0011

.0010

.0015

.0015

.0021

.0026

.0033
PROGRESS REPORT I05

EXAMPLESHOWING RELATION existing between

POSSIBLE DIMENSIONS OA~L/M/T WASTES? ANO

//VSPECT/ON Pl~(SG G/?G£T<S

2S40 Mat.

2S0O Min.

\ +ooo4\ [12504

'^ft.ooo7T)l.2S07

Net To/eranee- 003^9-

^-0004} 536

-00071 //J2533

Example show/nc relation ex/st/ng between

POSSIBLE ll/MENS/ONS OF L/M/T MASTER AND

/ MSPEC7-/0 A/ /?//V<y GtiGES If I.Z4BO Max.

J 1 I.Z440 Min'.

Work io he Gajed

y -.0000] ri. IZ48°-.ooo3y\l.

7-2480

2477

£xtre/rj e To/e ra. nce= . 004.

Kn V

LimiTMfiSTER Gages

} +.0O0O]

1.2440

i-.OOOjJ

2440

2443

Net Tolerance -.0034

~Y -.0004

2480

^ ".0007

J I'- Inspection Gages

+.0004A [12444

1.2440 U

^

+.0007] y.2447

Max. Looseness by Extreme. Tolerance — 0J00

" " " Net" » —.0034

Max. Tightness iy Extreme To/erance= 002,0

Net =.oo2G

Fig. 44.

Illustration of relation between dimensions of work and gages
io6 NATIONAL SCREW THREAD COMMISSION

TABLE 31.—Tolerances on Master Thread Gages for Loose-Fit and Medium-Fit

Work (This applies to both standard and limit master gages)

Threads per inch

Allowable

variation in lead between

any two

threads not

farther apart than length

of engage- ment

Allowable

variation in one-half angle of thread gages

Allowable

tolerances on

diameters of minimum

thread gages

Allowable

tolerances on

diameters of maximum

thread gages

<to 6 ±0. 0005 ±0° 5' +0.0000 —u. uuuu + .0006 - .0006

7 to 10 . ± .0004 ±0° 5' + .0000 - .0000 + .0004 - .0004

11 to 18 ± .0003 ±0° 10' + .0000 - .0000 + .0004 - .0004

20 to 28 ± .0002 ±0° 15' + .0000 - .0000 + .0003 - .0003

30 to 40 ± .0002 ±0° 20' + .0000 - .0000 + .0002 - .0002

44 to 80 ± .0002 ±0° 30' + .0000 - .0000 + .0002 - .0002

TABLE 32.—Suggested Manufacturing Tolerances for Inspection Gages for LooseFit and Medium-Fit Work

Threads per inch

Allowable

variation in lead between

any two

threads not

farther apart than length

of engage- ment

Allowable

variation in one -half angle of thread gages

Allowable

tolerances on

diameters of minimum

thread gages

Allowable

tolerances on

diameters of maximum

thread gages

4 to 6.

.

7 to 10.

11 to 18

20 to 28

30 to 40

44 to 80

±0.0006

± .0005

± .0004

± .0003

± .0002

± .0002

±0° 5'

±0° 10'

±0° 15'

±0° 20'

±0° 30'

±0° 45'

+0.0006 0.006 + .0015 .0015 + .0004 .0004 + .0010 .0010 + .0004 .0004 + .0008 .0008 + .0003 .0003 + .0006 .0006 + .0002 .0002 + .0005 .0005 + .0002 .0002 + .0004 .0004
PROGRESS REPORT 107

TABLE 33.—Suggested Manufacturing Tolerances for Working Gages for Loose-Fit and Medium-Fit Work

Threads per inch

Allowable

variation in lead between

any two

threads not

farther apart than length

of engage- ment

Allowable

variation in one -half angle of thread gages

Allowable

tolerances on

diameters of minimum

thread gages

Allowable

tolerances on

diameters of maximum

thread gages

4to6 ^ ±0.0006 ±0° 5' +0.0015 —0.0015 + .0025 - .0025

7 to 10 ± .0005 ±0° 10' + .0010 - .0010 + .0020 - .0020

11 to 18 ± .0004 ±0° 15' + .0008 — .0008

.0015 - .0015

20 to 28 ± .0003 ±0° 20' + .0006 - .0006 + .0012 - .0012

30 to 40 ± .0002 ±0° 30' + .0005 - .0005 + .0010 - .0010

44 to 80 ± .0002 ±0° 45' + .0004 - .0004 + .0006 - .0006

TABLE 34.—Master Gage Tolerances for Class III, Close-Fit Work (This applies to both standard and limit master gages)

Threads per inch

Allowable

variation in lead between

any two

threads not

farther apa:t than length

of engage- ment

Allowable

variation in one-half angle of thread gages

Allowable

tolerances on

diameters of minimum

thread gages

Allowable

tolerances on

diameters of maximum

thread gages

4 to 6..

7 to 10.

11 to 18

20 to 28

30 to 40

44 to 80

±0. 00025

± .0002

± .00015

± .0001

± .0001

± .0001

± 2' 30"

± 2' 30"

± 5' 00"

± 7' 30"

±10' 00"

±15' 00"

+0. 0000 + .0003 -0. 0000 - .0003 + . 0000 + .0002 - .0000 - . 0002 + . 0000 + . 0002 - . 0000 - . 0002 + . 0000 + .00015 - . 0000 — . 00015 + .0000 + .0001 - . 0000 - . 0001 + . 0000 + .0001 - . 0000 - . 0001

APPENDIX 7. TYPICAL SPECIFICATIONS FOR SCREW-THREAD PRODUCTS

(a) Material.—The material used shall be cold-drawn Bessemer steel automatic

screw stock.

(6) Composition—

Carbon, 0.08 to 0.16 per cent, Manganese, 0.50 to 0.80 per cent, Phosphorus, 0.09 to 0.13 per cent, Sulphur, 0.075 to 0.13 per cent.
I08 NATIONAL SCREW THREAD COMMISSION

(c) Method op Manufacture.—Bolts and nuts may be either rolled, milled, or machine cut, so long as they meet the specifications herein provided.

(d) Workmanship.—All bolts and nuts must be of good workmanship and free from all defects which may affect their serviceability.

(e) Finish.—All bolts and nuts to be semifinished; that is, the bodies to be machined, underside of head and nut faced, upper face of head and nut to be chamfered

at an angle of 30°, leaving a circle equal in diameter to the width of the nut.

(J) Form of Thread.—The form of thread shall be the National Form, as specified in Section III herein, and formerly known as the United States Standard or

Sellers Thread.

(#) Thread SERIES.—The pitches and diameters shall be as specified in Table 1, Section IV, herein, and known as the National Coarse-Thread Series.

(h) Class of Fit.—Class II-A, Medium Fit (Regular).

(») Dimensions—

(1) Nominal size: X inch.

(2) Number of threads per inch: 13. (3) Length under head : 3 inches ±0.05".

- (4) Minimum length of usable thread: 1 inch.

(5) Diameters: See Table 11, Section V.

(j) Tolerances and Allowances.—See Table 10, Section V.

(k) Nuts—

(1) Form: Hexagonal.

(2) Thickness: % inch io.oi".

(3) Short diameter (across flats) : ]/i inch/"'" ' 000 ' l— .005 . (I) Heads—

(1) Form: Hexagonal.

(2) Thickness: inch io.oi".

(3) Short diameter (across flats) : 7/$ inch{^~°'°00 ' I— .005". (m) Gages.—The gages used shall be such as to insure that the product falls within the tolerances as specified herein for Class II, Medium Fit (Regular).

The following gages are suggested and will be used by the purchaser

For the screw—

(1) A maximum or "Go" ring thread gage.

(2) A minimum or "Not Go" ring thread gage to check only the pitch diameter

of the thread.

(3) A maximum or "Go" plain ring to check the major diameter of the thread.

(4) A minimum or " Not Go" snap gage to check the major diameter of the thread. For the nut—

(1) A minimum "Go" thread plug gage.

(2) A maximum or "Not Go '

' thread plug gage to check only the pitch diameter.

(3) A "Go" plain plug gage to check the minor diameter.

(4) A "Not Go" plain plug gage to check the minor diameter of the thread.

(w) Inspection and Test.—Screws and nuts shall be inspected and tested as follows: At least three bolts and nuts shall be taken at random from each lot of ioo, or

fraction thereof, and carefully tested. If the errors in dimensions of the screws or nuts tested exceed the tolerance specified for this class, the lot represented by these samples shall be rejected.

(0) Delivery.—Unless otherwise specified the assembled bolts and nuts are to be

delivered in substantial wooden containers, properly marked, and each containing

100 pounds.
X. INDEX

Page

Allowance 7 Allo.wance (numerical values) 29, 38, 44, 52 Angle of helix {see Helix angle) 7 Angle of thread 7 Arrangement of report 5 Axis of screw 7 Base of thread 7 Basic 8

Class I, loose fit 23-32 Class II-A, medium fit (regular) 33-40

Class II-B, medium fit (special) 41-46 Class in, close fit 47-54

Class IV, wrench fit 55 Classification of fits 22 Clearance, crest 8 Clearance at major diameter '. 11 Clearance at minor diameter 11 Close fit, Class III " 47-54 Core diameter {see Minor diameter) 6 Crest 7 Crest clearance 8

Definitions 6 Depth of engagement 7 Depth of thread 7 Direction of tolerance on screw and nut 24, 33.41,47; 55 Effective diameter {see Pitch diameter) 6 Engagement, depth of 7 Engagement, length of 7, 23 Extreme tolerance 7 Finish 8 Sit 8 Form of thread 9 Future work of commission 84 Gage classification 60 Gage increment 8 Gage, inspection 60 Gage, limit master 60 Gage, standard master 60 Gage tolerances 81,82, 104, ro6, 107 Gage, working 60 Gages (fundamental statements) 58 Gages and methods of test 98-107 Gages for national pipe threads 63-66, 69-71

Hearings, public 89 Helix {see Screw helix) 6 Helix angle 7 Historical 93 Increment, gage 8 International standardization 84 Lead 7 Length of engagement 7, 23 Limits 8 Locknut threads 67,76 Loose fit, Class 1 23-32 Major diameter 6 Manual on national pipe threads 60

Page Marking of tools, gages, etc g Medium fit (regular), Class II-A 33-40 Medium fit (special),' Class II-B 4i-46 Minor diameter g National coarse thread series. . . . 17,19,30,39,45,53 National fine thread series 1 7, 20, 31, 40, 46, 54 Nationalfirehose coupling threads . . . 16,18,20,32 Nationalform ofthread 9 Nationalhosecouplingthreads 13, 18, 2r, 32 National pipe threads 19,60-83 Net tolerance g Neutral zone . g Nomenclature {see Terminology) 6 Notation 10,73,75,76 Number of threads

7 Organization of commission St gy Origin of commission

4j gg Outside diameter {see Major diameter) 6 Pipe thread gages 63-66,69-71 Pipe threa d manual g Pipe threads, straight 67,75 Pitch ' - Pitch diameter g Procedure of commission g9 Public hearings g9 Purpose of report .

Report, arrangement of Root

5

7

7

6

6

760

Screw axis Screw helix Screw thread Side of thread Standard temperature

Straight pipe threads 67, 75 Symbols 8, 67 Technical Temperature

Terminology Thread (see Screw thread) Thread angle Thread depth {see Depth of thread) Thread form Thread series adopted

Tolerance (definition of) Tolerance, extreme

Tolerance, net 8

Tolerance (explanation of) 56 Tolerances, gage 81, 82, 104, 106, 107 Tolerances (numerical values)

;

Class I, loose fit 29 Class II-A, medium fit (regular) 38

Class II-B, medium fit (special) 44

Class III, close fit 52 Uniform minimum nut

Utility of report 23

5 Wrench fit , Class IV 23,55 109