1978_2009.pdf

REAFFIRMED 2009FOR CURRENT COMMITTEE PERSONNELPLEASE E-MAIL CSasme.orgIntentionally left blank A M E R I C A N N A T I O N A L S T A N D A R D Preferred Metric Limits and Fits ANSI B4.2-1978 REAFFIRMED 1984 SECRETARIAT THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS PUBLISHED BY T H E A M E R I C A N S O C I E T Y O F M E C H A N I C A L E N G I N E E R S United Engineering Center 3 4 5 East 47th Street New York,N.Y.1001 7 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.Second printing-March 1979 Includes corrected pages iii,7,15,43,44,and 46.Copyright 1978 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS AIIRighn Resewed Printed in U.S.A.FOREWORD The American National Standards Committee EM was organized in June 1920,and it developed the American Standard ASA B4a-1925,Tolerances,Allowances and Gages for Metal Fits.As a result of committee work during World War I1 by ASA and ABC(American,British,Canadian),American Standard,Limits and Fits for Engineering and Manufacturing (Part I),ASA B4.1-1947,was produced.The preface to that document made significant reference to the contribution of the ABC meet-ings in developing agreement on five basic principles,four of whch apply to the present standard.These related to the desirability of establishing common definitions,a table of preferred basic sizes,a system of preferred tolerances and allowances,and a uniform method of applying tolerances.In 1973,the General Motors Corporation recognized a need for a metric standard similar to the IS0 R286 and published an interim standard which was later adopted as an ANSI Special Metric Publication,SR 11.The EM Standards Committee was reorganized in November 1975,and renamed“Standardization of Allowances and Tolerances for Manufactured Parts”.The first draft proposal of this standard was based on the principles noted above and utilized computer programs to implement the concept.The preferred basic sizes have been selected from the American National Standard for Preferred Metric Sizes for Round,Square and Hexagonal Metal Products,B32.4-1974,and the first choice sizes are all con-sistently rounded off from the Renard 10(R10)series of preferred numbers.A logical reduction or expan-sion of the first choice sizes can simply be achieved by utilizing the RS or R20 series of preferred numbers as explained in this standard.The selection of standard tolerance zones and preferred metric fits in this standard were based on inter-national and national standards shown in the following list:WORLD Is0 SYSTEM OF LIMITS AND FITS ISOIR286 PREFERRED TOLERANCE ZONES I s 0 1029 USA JIS B 0401 JAPAN ANSI 84.1(INCH STDI ANSI SR 11 UNI 7218 UN I 6388B9 ITALY BSI 4500 BSI 4500 U.K.NF E 02-131-135 NF E 02-100-118 FRANCE DIN 7157154155 DIN 7160/61 GERMANY JIS B 0401 CANADA NONE CSA 897.3 (INCH STDI AUSTRALIA AS 1654 AS 1654 The above standards have affected the availability of material stock,tooling and gages to the preferred IS0 tolerances throughout the world.Implementation of this standard by industry can greatly reduce cost in manufacturing.A draft proposal was circulated for letter ballot of the B4 Committee on October 16,1976.Comments received as a result of this ballot led to changes and subsequent approval of the text by the Committee.Final approval for this standard was granted by the American National Standards Institute(ANSI)on 8 March 1978.ACKNOWLEDGMENT Tables 2,3,4 and 5 of the text and Tables A1 through A24 of the Appendix were developed by Massey-Ferguson and full rights to usage have been conveyed to ASME.iii Intentionally left blank AMERICAN NATIONAL STANDARDS COMMITTEE B4 Standardization of Allowances and Tolerances for Manufactured Parts(The following is the roster of the Committee at the time of approval of this Standard)OFFICERS Knut 0.Kvnndand,Chairman C.J.Gomcr,Secretary COMMITTEE PERSONNEL AMERICAN MEASURING TOOL MANUFACTURERS ASSOCIATION R.P.Knittel,Glastonbury Gage,REB Industries.Inc.,Glastonbury,Connecticut AMERICAN SOCIETY or:MECHANICAL ENGINEERS,THE A.E.Merritt,Harnischfeger Corporation.Milwaukee,Wisconsin R.T.Woythal,Standard Machine Div.Kearney&Trecker Corporation,Milwaukee.Wisconsin ANTI-IRICTION BIARING MANUFACTURERS ASSOCIATION,THE K.D.MacKenrie,The Barden Corporation,Danbury,Connecticut COMPUTERS AND BUSINESS EQUIPMENT MANUFACTURERS ASSOCIATION A.E,Mall,International Business Machines Corporation,Endicott,New York METAL CUTTING TOOL INSTITUTE D.J.fmanuelli,Greenfield Tap&Die,A UnitedGreenfield Div.oITRW,Inc.,Greenfield.Massachusetts NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION F.V.Kupchak,Westinghouse Electric Corporation,R&D Center,Pittsburgh,Pennsylvania R.L.Mancini,Alternate,NationaJ Electrical Manufacturers Association,New York,New York NATIONAL FLUID POWER ASSOCIATION J.R.Luecke,National Ihid Power Association,Milwaukee,Wisconsin NATIONAL MACHINE TOOL BUILDERS ASSOCIATION F.S.Blackall,Ill,The Talt-Peirce Manufac