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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

SCREW THREADS: STANDARD PRACTICE FOR CALCULATING AND ROUNDING DIMENSIONS

ASME B1.30-2002

Revision of ASME B1.30M-1992

Date of Issuance: April 25, 2003

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.

ASME is the registered trademark of The American Society of Mechanical Engineers.

This code or standard was developed under procedures accredited as meeting the criteria for American National Standards. The Standards Committee that approved the code or standard was balanced to assure that individuals from competent and concerned interests have had an opportunity to participate. The proposed code or standard was made available for public review and comment that provides an opportunity for additional public input from industry, academia, regulatory agencies, and the public-at-large.

ASME does not “approve,” “rate,” or “endorse” any item, construction, proprietary device, or activity.

ASME does not take any position with respect to the validity of any patent rights asserted in connection with any items mentioned in this document, and does not undertake to insure anyone utilizing a standard against liability for infringement of any applicable letters patent, nor assume any such liability. Users of a code or standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, is entirely their own responsibility.

Participation by federal agency representative(s) or person(s) affiliated with industry is not to be interpreted as government or industry endorsement of this code or standard.

ASME accepts responsibility for only those interpretations of this document issued in accordance with the established ASME procedures and policies, which precludes the issuance of interpretations by individuals.

No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise,

without the prior written permission of the publisher.

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

Copyright © 2003 by

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS

All rights reserved Printed in U.S.A.

CONTENTS

Foreword iv

Committee Roster v

1. General 1

2. Rounding of Decimal Values 1

3. Calculations From Formulas 2

4. Thread Form Constants 2

Tables

1. Number of Decimal Places Used in Calculations 2

2. Example of External Inch Screw Threads, 1⁄2-28 UNEF-2A 4

3. Example of Internal Inch Screw Threads, 1⁄2-28 UNEF-2B 7

4. Example of External Inch Screw Threads, 19⁄64-36 UNS-2A 9

5. Example of Internal Inch Screw Threads, 19⁄64-36 UNS-2B 12

6. Example of External Metric Screw Threads, M12 1.75-4g6g 14

7. Example of Internal Metric Screw Threads, M12 1.75-6H 16

8. Example of External Metric Screw Threads, M13 0.9-4g6g 18

9. Example of Internal Metric Screw Threads, M13 0.9-6H 20

10. Thread Form Data 22

Nonmandatory Appendix

A Thread Characteristics Governed by this Standard 23

FOREWORD

The American National Standards Committee B1 for standardization of screw threads was organized in 1920 as sectional Committee B1 under the sponsorship of the American Engineering Standards Committee (later the American Standards Association, then the United States of America Standards Institute and as of October 6, 1969, the American National Standards Institute, Inc.), with the Society of Automotive Engineers and The American Society of Mechanical Engineers as joint sponsors. As a result, a great deal of effort was expended through the years toward development of several screw thread standards.

Recognizing the need to standardize the method of rounding decimal values in the calculation of screw thread dimemsions, the ASME Standards Committee B1 charged Subcommittee 30 with the responsibility for producing such a standard.

This Standard designated ASME B1.30 was developed only to serve as the basis for rounding of decimal values associated with the computation of screw thread dimensions.

The examples and formulas depicted within this Standard are for reference only and are presented only to clarify the rounding procedures described. When calculating the different thread characteristics for a particular thread form, refer to the appropriate ASME B1 standard for the formulas and methodology of calculation for that thread.

This Standard was originally approved as an American National Standard on June 29, 1992. This issue updates the 1992 issue and includes:

1. the addition of a note to para. 1.2 for the clarification of the use of this Standard for metric applications;

2. the addition of an exception in para. 3.1.3 to the number of decimal places for the allowance 2A when used in intermediate calculations as Td2;

3. the addition of the maximum external UN minor diameter, maximum and minimum internal pitch diameters and the minimum internal major diameter to the example in para. 3.2.1;

4. removal of Appendix A containing various common values for 60 deg thread elements. This was done because the values are either listed or can be calculated by formulas in other existing B1 standards;

5. the addition of an example for a standard metric size that is listed in ASME B1.13M and ISO 261;

6. the addition of an example for a special inch size showing how to round numbers with an infinite number of digits after the decimal point;

7. added a new Appendix A with a table listing the number of decimal places for each of the thread characteristics used in the examples in B1.30.

   Suggestions for improvement of this Standard will be welcome. They should be sent to Secretary, ASME B1 Standards Committee, Three Park Avenue, New York, NY 10016-5990 U.S.A.

   This revision was approved as an American National Standard on July 12, 2002.

   
   

   iv

   
   

   ASME STANDARDS COMMITTEE B1

   Standardization and Unification of Screw Threads

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

   
   

   OFFICERS

   1. L. Barrows, Chair

D. S. George, Vice Chair

J. R. Bird, Secretary

G. L. Allen, The L. S. Starrett Co.

A. L. Barrows, Kennametal-IPG

M. H. Bernier, Standard Nut and Bolt

COMMITTEE PERSONNEL

L. L. Lord, Caterpillar, Inc.

R. L. Tennis, Alternate, Caterpillar, Inc.

M. H. McWilliams, PMC Gage, Inc.

J. R. Bird, The American Society of Mechanical Engineers

F. G. Calderone, Quality Systems Implementers

J. Davis, U.S. Nuclear Regulatory Commission

L. N. Dixon, Jr., General Electric

R. Dodge, Pennoyer-Dodge Co.

G. A. Flannery, Mercury Gage Co.

D. Skierski, Alternate, Mercury Gage Co.

H. N. Frost, Defense Supply Center Philadelphia

D. S. George, Ford Motor Co.

J. R. Gervasi, Kerr Lakeside Inc.

J. Greenslade, Greenslade & Co.

L. C. Johnson, The Johnson Gage Co.

D. D. Katz, Precision Fittings

R. P. Knittel, Leitech / AMTMA

B. Larzelere, Deltronic Corp.

D. Miskinis, Kennametal-IPG

W. R. Newman, Facil LLC, USA

M. W. Rose, Southern Gage, Inc.

1. M. Satava, Consultant

2. Schwartz, Consultant

R. H. Searr, Conam Quantum Inspection and Testing

R. E. Seppey, Consultant

A. D. Shepherd, Jr., Emuge Corp.

A. G. Strang, Consultant

R. D. Strong, General Motors Corp.

A. F. Thibodeau, Swanson Tool Manufacturing, Inc.

R. C. Veale, Consultant

R. E. Vincent, Jr., General Plug Manufacturing Co.

C. J. Wilson, Industrial Fasteners Institute

F. W. Akstens, Alternate, Industrial Fasteners Institute

SUBCOMMITTEE 30 — ROUNDING OF VALUES

R. H. Searr, Chair, Conam Quantum Inspection and Testing

1. L. Barrows, Vice Chair, Kennametal-IPG

2. I. Armstrong, Naval Warfare Assessment Division

R. Dodge, Pennoyer-Dodge Co.

D. S. George, Ford Motor Co.

J. Greenslade, Greenslade & Co.

L. C. Johnson, The Johnson Gage Co.

D. D. Katz, Precision Fittings

W. R. Newman, Facil LLC, USA

M. W. Rose, Southern Gage, Inc.

1. M. Satava, Consultant

2. Schwartz, Consultant

R. E. Seppey, Consultant

A. D. Shepherd, Jr., Emuge Corp.

A. G. Strang, Consultant

R. D. Strong, General Motors Co.

R. C. Veale, Consultant

C. J. Wilson, Industrial Fasteners Institute

F. W. Akstens, Alternate, Industrial Fasteners Institute

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ASME B1.30-2002

SCREW THREADS: STANDARD PRACTICE FOR CALCULATING AND ROUNDING DIMENSIONS

1. GENERAL

   1. Purpose

      The purpose of this Standard is to establish uniform and specific practices for calculating and rounding the numeric values used for inch and metric screw thread design data dimensions only. No attempt is made to establish a policy of rounding actual thread characteris- tics measured by the manufacturer or user of thread gages. Covered is the Standard Rounding Policy regard- ing the last figure or decimal place to be retained by a numeric value and the number of decimal places to be retained by values used in intermediate calculations of thread design data dimensions. Values calculated to this Standard for inch and metric screw thread design data dimensions may vary slightly from values shown in existing issues of ASME B1 screw thread standards and are to take precedence in all new or future revisions of ASME B1 standards as applicable except as noted in para. 1.2.

      
      

   2. Metric Application

      Allowances (fundamental deviations) and tolerances for metric M and MJ screw threads are based upon formulas, which appear in applicable standards. Values of allowances for standard tolerance positions and val- ues of tolerances for standard tolerance grades are tabu- lated in these standards for a selection of pitches. Rounding rules specified below have not been applied to these values but have followed practices of the Inter- national Organization for Standardization (ISO). For pitches, which are not included in the tables, standard formulas and the rounding rules specified herein are applicable.

      
      

      NOTE: ISO rounding practices, for screw thread tolerances and allowances, use rounding to the nearest values in the R40 series of numbers in accordance with ISO 3. In some cases, the rounded values have been adjusted to produce a smooth progression. Since the ISO rounded values have been standardized internationally, for metric screw threads, it would lead to confusion if tolerances and allowances were recalculated using B1.30 rules, for use in the USA. B1.30 rounding rules are, therefore, only applicable to special threads where tabulated values do not exist in ISO standards. Values calculated using the ISO R40 series values may differ from those calculated using B1.30. In such a case the special thread values generated using B1.30 take precedence.

2. ROUNDING OF DECIMAL VALUES

   The following rounding practice represents the method to be used in all new or future revisions of ASME B1 thread standards.

   NOTE: It is recognized that this Standard is not in agreement with other published documents, e.g., ASME SI-9, Guide for Metrication of Codes and Standards SI (Metric) Units, and IEEE/ASTM SI 10, Standard for Metric Practice. The rounding practices used in the forenamed documents are designed to produce even distribution of numerical values. The purpose of this document is to define the most practical and common used method of rounding numerical thread form values. Considering today’s technology, application of this method is far more practical in the rounding of thread form values.

   
   

   1. Rounding Policy

      1. When the figure next beyond the last figure or place retained is less than 5, the figure in the last place retained is kept unchanged.

         EXAMPLE:

         
         

         1.012342	1.01234
         1.012342	1.0123
         1.012342	1.012

         
         

      2. When the figure next beyond the last figure or place retained is greater than 5, the figure in the last place retained is increased by 1.

         EXAMPLE:

         1.56789 1.5679

         1.56789 1.568

         1.56789 1.57

         
         

      3. When the figure next beyond the last figure or place retained is 5, and:

1. there are no figures, or only zeros, beyond this 5, the last figure should be increased by 1;

   EXAMPLE:

   
   

   1.01235	1.0124
   1.0123500	1.0124
   1.012345	1.01235
   1.01234500	1.01235

   
   

2. if the 5 next beyond the figure in the last place to be retained are followed by any figures other than zero,

1