Screw Threads: Nomenclature, Definitions, and Letter Symbols

A N A M E R I C A N N A T I O N A L S T A N D A R D

ASME B1.7-2006

(Revision of ANSI/ASME B1.7M-1984)

ASME B1.7-2006

(Revision of ANSI/ASME B1.7M-1984)

Screw Threads: Nomenclature, Definitions, and Letter Symbols

AN AMERICAN NATIONAL STANDARD

Three Park Avenue • New York, NY 10016

Date of Issuance: November 17, 2006

This Standard will be revised when the Society approves the issuance of a new edition. There will be no addenda or written interpretations of the requirements of this Standard issued to this edition.

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The American Society of Mechanical Engineers Three Park Avenue, New York, NY 10016-5990

Copyright © 2006 by

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS

All rights reserved Printed in U.S.A.

CONTENTS

Foreword v

Committee Roster vi

1. General 1

2. Definition of Terms 1

Figures

1. Allowance 2

2. Axis of Thread 2

3. Best Wire Size 2

4. Blunt Start Thread 3

5. Bottom of Chamfer 4

6. Clearance Flank 4

7. Countersink 4

8. Crest 4

9. Root and Crest Truncation 5

10. Fundamental Deviation 6

11. Metric Tolerance System for Screw Threads 7

12. Element 7

13. Flank 7

14. Flank Angle 7

15. Flat Form 7

16. Following Flank 8

17. Gauge Plane 8

18. Height of Fundamental Triangle 8

19. Height of Thread 9

20. Height of Thread Engagement 9

21. Helix 9

22. Helix Variation (Drunken Thread) 9

23. Incomplete Thread 10

24. Interference Fit 11

25. Internal Thread 11

26. Lead 11

27. Leading Flank 11

28. Gaging Length 11

29. Length of Assembly 11

30. Length of Thread Engagement 12

31. Load Flank 12

32. Major Clearance 12

33. Major Diameter, External Thread 12

34. Major Diameter, Internal Thread 12

35. Major Diameter, Internal Thread (Rounded Form) 12

36. Major Diameter, Taper Thread 12

37. Minor Clearance 13

38. Minor Diameter, External Thread (Flat Form) 14

39. Minor Diameter, External Thread (Rounded Form) 14

40. Minor Diameter, Internal Thread 14

41. Minor Diameter, Taper Thread 14

42. Multiple Start Thread 14

    iii

43. Pitch 14

44. Pitch Cone 14

45. Pitch Cylinder 14

46. Pitch Diameter, External Thread 15

47. Pitch Diameter, Internal Thread 15

48. Plane of Vanish Point 15

49. Profile, Basic Thread 16

50. Root Radius 16

51. Screw Thread 16

52. Sharp Crest and Root 16

53. Shear Area 17

54. Straight Thread 18

55. Thread Angle 23

56. Thread Ridge Thickness 23

57. Truncation 23

58. Vanish Cone 24

Tables

1. General Symbols 19

2. ISO General Symbols 20

3. Thread Series Designations 21

4. ISO Thread Series Designations 22

   Nonmandatory Appendices

   1. Superseded Thread Series Designations 25

   2. ISO Symbols for Screw Threads 26

   3. Greek Alphabet 27

      
      

      iv

      
      

      FOREWORD

      
      

      The first revision of ASA B1.7-1949, the first American Standard on Nomenclature, Definitions, and Letter Symbols for Screw Threads, was approved in January 1965. These earlier definitions and symbols were subsequently published as appendix material in ASA B1.1, B2.1, and B2.2. As such they underwent some revision over the years. A draft based on such revisions, dated July 1961, was prepared by Subcommittee 8 and widely circulated by the sponsors for comment. Ex- tensive comments were received from members of Sectional Committee B1, B2, B4, and others, which were reviewed and acted upon at a meeting of Subcommittee 8, held November 28, 1961. A second revised draft, dated July 1962, was prepared and submitted to the American-British- Canadian Conference on Engineering Standards, held in Harriman, New York on September 22–26, 1962. Suggested revisions agreed upon by the conference were embodied in the draft,

      which was then submitted to letter ballot by Sectional Committees B1 and B2 on July 9, 1963. Further refinements were made in the proposal because of comments received from the sec-

      tional committee ballots, and a new draft was issued in May 1964. The draft was submitted to the American Standards Association for approval and designation as an American Standard. This was granted on January 19, 1965, and reaffirmed in 1972 by the American National Standards In- stitute as American National Standard ANSI B1.7.

      Following the 1972 reaffirmation, comments from members of the American National Stan- dards Committee B1, and others, indicated that a complete revision be undertaken. A new draft was prepared and submitted in March 1975 to Subcommittee 7 for review and approval. After numerous comments and subsequent changes, the proposed standard was submitted to and ap- proved by American National Standards Committee B1. The document was then transmitted to the Secretariat and ANSI in October 1976. It was approved as an American National Standard, ANSI B1.7-1977, on September 16, 1977.

      Within the period from 1977 to 1984 there was considerable B1 standards activity in the de- velopment of metric screw thread standards for U.S. usage. ISO standards were blended with ANSI standards, requiring many revisions in ANSI symbology and definitions of terms. ISO sym- bols were adopted, except those where a change from American practice would confuse the gen- eral understanding of the elements symbolized. Also, many ISO definitions were incorporated into American definitions in order to facilitate the correct interpretation of both ISO and ANSI terminology. These revisions were approved and designated as American National Standard ANSI/ASME B1.7M-1984, on November 2, 1984.

      Screw thread standards are constantly being revised as required by the ASME B1 Committee. Additionally, the title of this document was changed to “Screw Threads: Nomenclature, Defini- tions, and Letter Symbols.” This revision was approved and designated by the American Na- tional Standards Institute on September 11, 2006.

      
      

      v

      
      

      ASME B1 COMMITTEE

      Screw Threads

      
      

      (The following is the roster of the Committee at the time of approval of this Standard.)

      
      

      STANDARDS COMMITTEE OFFICERS

      
      

      1. L. Barrows, Chair

D. S. George, Vice Chair

A. L. Guzman, Secretary

STANDARDS COMMITTEE PERSONNEL

A. L. Barrows, Kennametal, Inc. B. Larzelere, Corresponding Member, Deltronic Corp.

F. G. Calderone, Corresponding Member, Quality L. L. Lord, Corresponding Member, Consultant Systems Implementers M. H. McWilliams, PMC Lonestar

L. N. Dixon, Jr., General Electric D. R. Maisch, Alternate, PMC Lonestar

R. Dodge, Pennoyer-Dodge Co. D. Miskinis, Kennametal, Inc.

D. Everett, National Institute of Standards and Technology W. R. Newman, Corresponding Member, Consultant

1. A. Flannery, Corresponding Member, Mercury Gage Co. D. R. Oas, Seaway Bolt & Specials Corp.

2. N. Frost, Defense Supply Center M. W. Rose, Glastonbury Southern Gage

J. O. Gehret III, Vermont Thread Gage, LLC W. A. Watts, Alternate, Glastonbury Southern Gage

D. S. George, Ford Motor Co. E. Schwartz, Consultant

J. R. Gervasi, Kerr Lakeside, Inc. R. H. Searr, Member Emeritus, Mak Tool & Gage

J. Greenslade, Greenslade & Co. B. F. Sheffler, Dresser-Rand Co.

L. C. Borowski, Alternate, Greenslade & Co. A. D. Shepherd, Jr., Emuge Corp.

A. L. Guzman, The American Society of Mechanical Engineers D. Skierski, Sterling Gage & Calibration, LLC

R. J. Hukari, SPS Technologies R. D. Strong, General Motors Vehicle Engineering Center

L. C. Johnson, The Johnson Gage Co. A. F. Thibodeau, Member Emeritus, Swanson Tool

D. D. Katz, Precision Fittings Manufacturing, Inc.

R. P. Knittel, Leitech-US Ltd. R. E. Vincent, Jr., General Plug Manufacturing Co.

P. A. Larouche, Swanson Tool Manufacturing C. J. Wilson, Industrial Fasteners Institute

SUBCOMMITTEE 7 — NOMENCLATURE, DEFINITIONS, AND LETTER SYMBOLS FOR SCREW THREADS

B. F. Sheffler, Chair, Dresser-Rand Co. D. D. Katz, Precision Fittings

A. L. Barrows, Kennametal, Inc. R. P. Knittel, Leitech-US Ltd.

F. G. Calderone, Corresponding Member, Quality Systems B. Larzelere, Corresponding Member, Deltronic Corp. Implementers W. R. Newman, Corresponding Member, Consultant

L. N. Dixon, Jr., General Electric M. W. Rose, Glastonbury Southern Gage

R. Dodge, Pennoyer-Dodge Co. E. Schwartz, Consultant

D. S. George, Ford Motor Co. R. H. Searr, Member Emeritus, Mak Tool & Gage

J. Jennings, Corresponding Member, Naval Surface A. D. Shepherd, Jr., Emuge Corp. Warfare Center R. E. Spencer, Faber Enterprises, Inc.

L. C. Johnson, The Johnson Gage Co. C. J. Wilson, Industrial Fasteners Institute

vi

ASME B1.7-2006

SCREW THREADS: NOMENCLATURE, DEFINITIONS, AND LETTER SYMBOLS

1. GENERAL

   1. Scope

      The purpose of this Standard is to establish a uniform practice for standard screw threads with regard to the following:

      1. screw thread nomenclature

      2. letter symbols for the designating features of a screw thread for use on drawings, in tables that set forth dimensional standards, in other records, and for ex- pressing mathematical relationship

         This Standard consists of: a glossary of terms, illus- trations, an illustrated table showing the application of symbols, and a table of thread series designations. Many of the terms and symbols specified in this Standard vary considerably from those prior to the 1984 issue, because ISO terms and symbols have been adopted where the intended definition is the same.

         
         

   2. References

      The following is a list of publications referenced in this Standard.

      ANSI/CGA V-1, National Gas Screw Threads1 Publisher: Canadian Gas Association (CGA), 350 Sparks

      Street, Ottawa, Ontario K1R 7S8, Canada

      ASME B1.20.7, Hose Coupling Screw Threads ASME Y14.5M, Dimensioning and Tolerancing

      Publisher: The American Society of Mechanical Engi- neers (ASME), Three Park Avenue, New York, NY 10016-5990; Order Department: 22 Law Drive, P.O. Box 2300, Fairfield, NJ 07007-2300

      ISO 7-1, Pipe Threads Where Pressure Tight Joints are Made on Threads—Part 1: Designation, Dimensions, and Tolerances

      ISO 228-1, Pipe Threads Where Pressure Tight Joints are Not Made on the Threads—Part 1: Designation, Di- mensions, and Tolerances

      ISO 1502, ISO General Purpose Metric Screw Thread- Gauging

      ISO 2901, ISO Metric Trapezoidal Screw Threads ISO 2902, ISO Metric Trapezoidal Screw Threads ISO 2903, ISO Metric Trapezoidal Screw Threads ISO 2904, ISO Metric Trapezoidal Screw Threads ISO/R1501, ISO Miniature Screw Threads

      
      

      1 May also be obtained from American National Standards In- stitute (ANSI), 25 West 43rd Street, New York, NY 10036.

      Publisher: International Organization for Standardiza- tion (ISO), 1 rue de Varembé, Case Postal 56, CH-1211, Genève 20, Switzerland/Suisse

      
      

   3. Federal Government Use

      When this Standard is approved by the Department of Defense and Federal agencies, and is incorporated into FED-STD-H28/1, Screw Thread Standards for Federal Services, Section 1, the use of this Standard by the Fed- eral Government is subject to all requirements and lim- itations of FED-STD-H28/1.

      
      

2. DEFINITION OF TERMS

The definitions presented herein are listed alphabeti- cally and apply generally to all forms of screw threads, thread gages, and thread measurements. They relate to the following:

1. types of screw threads

2. size and fit of threaded parts in general

3. geometric elements, attributes, and dimensions of screw threads

ISO nomenclature is used where the exact meaning is coincident with the U.S. practice.

actual fit: the measured difference, subject to measure- ment uncertainty, before assembly, between the sizes of two mating parts that are to be assembled.

actual size: the measured size of a characteristic or ele- ment subject to measurement uncertainty.

addendum: the addendum of an external thread is the ra- dial distance between the major and pitch cylinders or cones, respectively. The addendum of an internal thread is the radial distance between the minor and pitch cylin- ders or cones, respectively. This term applies to those threads having a recognized pitch cylinder or pitch cone.

allowance: a prescribed difference between the maximum material limits of mating parts. It is the minimum clear- ance (positive allowance) or maximum interference (negative allowance) between such parts. It is numeri- cally equal to the absolute value of ISO term funda- mental deviation (see Fig. 1).

attribute: nondimensional thread element(s) and charac- teristic(s), taken singly or in a group. Inspection/evalu- ation by limit gages is an attribute inspection.

axis of thread: the axis of the thread pitch cylinder or cone (see Fig. 2).

1