U.S. METRIC STUDY INTERIM REPORT ENGINEERING STANDARDS U.S. METRIC STUDY ORIS ii , - lilts of substudies of the U.S. Metric Study, while being evaluated for the preparation of a comprehensive report to the Congress, are being led in the interim as a series of NBS Special Publications. The titles I'lividual reports are listed below. interniUional Standards (issued December 1970, SD Catalog No. C 1 3. 1 0:345- 1 , Price $ 1 .25) NBS SP345-2 Federal Government: Civilian Agencies (in press) NBS SP345-3 Commercial Weights and Measures (in press) NBS SP345-4 The Manufacturing Industry (in press) fv Q c J. I p_ p _ Nonmanufacturing Businesses (in press) o Education (in press) , . 45-7 The Consumer (in press) NBS SP345-8 International Trade (in press) NBS SP345-9 Department of Defense (in press) NBS SP345-iO A History of the Metric System Controversy in the United States (in press) Engineering Standards, this publication Testimony of Nationally Representative Groups (in press) 5: hed in August 1971 ^ :;'^ , i,..,,,,^ Tb'^"': , heep issued, and m;- s. Government dd one- ent to a jf order. 1 U.S. METRIC STUDY INTERIM REPORT ENGINEERING STANDARDS Eleventh in a series of reports prepared for the Congress U.S. METRIC STUDY Daniel V. De Simone, Director National Bureau of Standards Special Publication 345- 1 UNITED STATES DEPARTMENT OF COMMERCE Maurice H. Stans, Secretary NATIONAL BUREAU OF STANDARDS Lewis M. Branscomb, Director Nat. Bur. Stand. (U.S.). Spec. Publ. 345-11. 264 pages (July 1971) CODEN: XNBSA Issued July 1971 For sale by the Superintendent of Documents. U.S. Government Printing Office Washington, D.C.. 20402 - Price $2 Stock Number 0303-0835 (Order by SD Catalog No. C 13.10:345-1 1). Price $2.00 LETTER OF TRANSMITTAL THE HONORABLE PRESIDENT OF THE SENATE THE HONORABLE SPEAKER OF THE HOUSE OF REPRESENTATIVES SIRS: I have the honor to present the eleventh in the series of interim reports stemming from the U.S. Metric Study, prepared by the National Bureau of Standards. This Study was authorized by PubUc Law 90-472 to reduce the many un- certainties concerning the metric issue and to provide a better basis upon which the Congress may evaluate and resolve it. I shall make a final report to the Congress on this Study in August 1971. In the meantime, the data and opinions contained in this interim report are being evaluated by the Study team at the National Bureau of Standards. My final report to you will reflect this evaluation. Respectfully submitted, Secretary of Commerce Enclosure iii LETTER OF TRANSMITTAL Honorable Maurice H. Stans Secretary of Commerce Dear Mr. Secretary: I have the honor to transmit to you another interim report of the U.S. Met- ric Study, which is being conducted at the National Bureau of Standards at your request and in accordance with the Metric Study Act of 1 968. The Study is exploring the subjects assigned to it with great care. We have tried to reach every relevant sector of the society to elicit their views on the metric issue and their estimates of the costs and benefits called for in the Metric Study Act. Moreover, all of these sectors were given an opportunity to testify in the extensive series of Metric Study Conferences that were held last year. On the basis of all that we have been able to learn from these conferences, as well as the numerous surveys and investigations, a final report will be made to you before August 1971 for your evaluation and decision as to any recommendations that you may wish to make to the Congress. The attached interim report includes data and other opinions that are still being evaluated by us to determine their relationship and significance to all of the other information that has been elicited by the Study. All of these evaluations will be reflected in the final report. Sincerely, Lewis M. Branscomb, Director National Bureau of Standards Enclosure iv FOREWORD This report concerns the relationship of measurement units to engineering standards. Although it is addressed primarily to the issues posed by Section 3 of the Metric Study Act (Public Law 90-472). it is of necessity related also to international standards, a subject covered by a previous report. Reports covering other substudies of the U.S. Metric Study are listed on the inside front cover. All of these, including this report, are under evalua- tion. Hence, they are published without prejudice to the comprehensive re- port on the entire U.S. Metric Study, which will be sent to the Congress by the Secretary of Commerce in August of 1971. This report was prepared by a Metric Study task force, headed by Dr. Robert D. Stiehler and including Mr. Gustave Shapiro, Mr. Robert J. Klein, Mr. Harry Stoub, Mr. Arthur G. Strang, and Mr. Theodore R. Young, all of the National Bureau of Standards. We are grateful to Mr. Frank Masterson and Mr. R. B. Belford, President and Technical Director, respectively, of the Industrial Fasteners Institute, for permission to include their first progress report on "A Study to Develop an Optimum Metric Fastener System." Their report, which appears as Ap- pendix V of this volume, illustrates the manner in which innovations in en- gineering standards can be achieved. In this as in all aspects of the U.S. Metric Study, the program has bene- fited from the independent judgment and thoughtful counsel of its advisory panel and the many other organizations, groups, and committees that have participated in the Study. Daniel V. De Simone, Director U.S. Metric Study V 5 TABLE OF CONTENTS Page Letters of Transmittal iii, iv Foreword v 1. Executive Summary 1 2. Summary of Conclusions and Recommendations 6 3. Purpose of Standards Survey 9 4. Scope of Standards Survey 10 5. Definitions 12 6. Function of Engineering Standards 14 7. Compatibility of Standards 17 8. Development Process for Engineering Standards 18 9. Magnitude of Standardization Effort 25 10. Measuring Units in Engineering Standards 31 11. Dimensional Specifications 34 12. Quality Specifications 43 13. Methods of Test 45 14. Descriptive Standards 47 15. I EC and Electrical Engineering Standards 48 16. ISO Recommendations 67 17. Steel 90 18. Nonferrous Metals 93 19. Plastics 96 20. Rubber 99 21. Anti-Friction Bearings 101 22. Building Construction and Materials 104 23. Pipe and Tubing 107 24. Screw Threads and Fasteners 1 1 25. Discussion 129 Appendices: I. Public Law 90-472 132 II. ISO Recommendation R 1000- Rules for the Use of Units of the International System of Units and a Selection of the Decimal Multiples and Submultiples of the SI Units 133 III. ASTM E380-70- Metric Practice Guide 152 IV. Compatibility of Screw Threads 187 V. First Progress Report of Industrial Fasteners Institute on a Study to Develop an Optimum Metric Fastener System 195 vi 1. EXECUTIVE SUMMARY Public Law 90-472^ approved on August 9, 1968 authorized the Secretary of Commerce to make a study to determine the advantages and disad- vantages of increased use of the metric system in the United States. The Congress in passing this law recognized the close relationship between en- gineering standards and measurement units and authorized a study to deter- mine the feasibility of retaining and promoting international use of dimen- sional and other engineering standards based on the customary measurement units of the United States. Section 3 of this act is specifically directed to this issue and states: In conducting the studies and developing the recommendations required in this Act. the Secretary shall give full consideration to the ad- vantages, disadvantages, and problems associated with possible changes in either the system of measurement units or the related dimensional and engineering standards currently used in the United States, and specifically shall — (1) investigate the extent to which substantial changes in the size, shape, and design of important industrial products would be neces- sary to realize the benefits which might result from general use of metric units of measurement in the United States; (2) investigate the extent to which uniform and accepted engineering standards based on the metric system of measurement units are in use in each of the fields under study and compare the extent to such use and the utility and degree of sophistication of such metric stand- ards with those in use in the United States; and ' See app. 1 for the full text of this law. 1 2 ENGINEERING STANDARDS (3) recommend specific means of meeting the practical difficulties and costs in those areas of the economy where any recommended change in the system of measurement units and related dimensional and engineering standards would raise significant practical difficul- ties or entail significant costs of conversion. The last part of section 3, Public Law 90-472, dealing with the difficulties and costs of conversion is not within the scope of this report. Costs of con- version are considered in the report on the Manufacturing Industry, SP345- 4. The cost of issuing engineering standards based on metric measurement units would be largely absorbed during the regular revision of the present standards. Metric dimensional specifications for standard parts and products would be largely based on national and international standards used in other countries. The cost of development of new standards incorporating latest knowledge and technological capabilities would be mainly the cost of technological improvement. On the other hand, revision of engineering stan- dards in a crash program solely to incorporate metric measurement units could cost many millions of dollars. However, a crash program has not been considered since it is neither necessary nor feasible. Since the passage of Public Law 90-472, the increasing worldwide use of the metric system, which was the primary concern leading to its passage, has now encompassed virtually all countries of the entire world.