1987_2018.pdf

REAFFIRMED 2018Intentionally left blank AN AMERICAN NATIONAL STANDARD Class 5 Interference-Fit Thread ASME/ANSI B1.12-I 987(REVISION OF ANSI B1.12-1972)The American Society of Mechanical Engineers 345 East 47th Street,New York,N.Y.1001 7-Date of Issuance:November 15,1987 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.This code or standard was developed under procedures accredited as meeting the criteria for American National Standards.The Consensus Committee that approved the code or standard was balanced to assure that individuals from competent and concerned interests have had an oppor-tunity to participate.The proposed code or standard was made available for public review and comment which provides an opportunity for additional public input from industry,academia,reg-ulatory 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 byfederal agency representativek)or personk)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 issued in accordance with governing ASME procedures and policies which preclude the issuance of interpretations by individual vol-unteers.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.Copyright 0 1987 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All Rights Reserved Printed in U.S.A.FOREWORD(This Foreword is not part of ASME/ANSI B1.12-1987.)Interference-fit threads are threads in which the externally threaded member is larger than the internally threaded member when both members are in the free state and which,when assembled,become the same size and develop a holding torque through elastic compression,plastic movement of material,or both.By custom,these threads are designated as Class 5.Tentative Class 5 fit threads were first published by the National Screw Thread Commission(1928),and alternate Class 5 appeared in the 1944 Handbook H28.These standards were helpful in stabilizing design;however,in spite of restrictive tolerances,loosening or breakage of externally threaded members has been all too frequent.Also,minimum and maximum torque values were established,the validity of which has been generally accepted.The tentative and alternate standards,which were based on National Bureau of Standards and industry research,testing,and field study,represent the first attempt to establish an Amer-ican standard for interference-fit threads.These specifications are published in Appendix A.In 1947,ASA Sectional Committee B1 on Screw Threads established Subcommittee 10 under the chairmanship of Harry Marchant to study the problems of interference fits.A subgroup of the subcommittee,chaired by W.S.Brown,conducted a comprehensive survey of design,production,and driving practices in the automotive,implement,railroad,and fastener indus-tries and found that all were experiencing difficulty.Typical problems were:(a)the variety of materials and heat treatments used for externally threaded members;(b)variations resulting from rolling,cutting,or grinding external threads;(c)the huge variety of chemical analyses and physical and mechanical properties encoun-tered in the forged,cast,die cast,and rolled materials into which the externally threaded members are driven;(d)the widely varying effects of chemical coatings,platings,and lubricants;and(e)the inability to closely control sizes of tapped holes in various materials.It was impossible to establish a standard at that time,but it was agreed that interference-fit threads could not be eliminated in design of equipment and that a workable standard was essential.In 1951,Subcommittee 10,later renumbered 12,established a research subgroup which conducted extensive tests under a variety of conditions.The work of this research subgroup and a report of subsequent research and field experience is described in the article“New Class 5 Interference Fit Thread”by W.G.Waltermire,which appeared in the September 6,1956 issue of Machine Design.This Trial American Standard was predicated on the following conclusions,which were drawn from the research and field experience for developing holding torque through plastic movement of ma