REAFFIRMED2009FORCURRENTCOMMITTEEPERSONNELPLEASEE-MAILCS@asme.orgIntentionallyleftblankAMERICANNATIONALSTANDARDPreferredMetricLimitsandFitsANSIB4.2-1978REAFFIRMED1984SECRETARIATTHEAMERICANSOCIETYOFMECHANICALENGINEERSPUBLISHEDBYTHEAMERICANSOCIETYOFMECHANICALENGINEERSUnitedEngineeringCenter345East47thStreetNewYork,N.Y.10017Nopartofthisdocumentmaybereproducedinanyform,inanelectronicretrievalsystemorotherwise,withoutthepriorwrittenpermissionofthepublisher.Secondprinting-March1979Includescorrectedpagesiii,7,15,43,44,and46.Copyright@1978byTHEAMERICANSOCIETYOFMECHANICALENGINEERSAII'RighnResewedPrintedinU.S.A.FOREWORDTheAmericanNationalStandardsCommitteeEMwasorganizedinJune1920,anditdevelopedtheAmericanStandardASAB4a-1925,Tolerances,AllowancesandGagesforMetalFits.AsaresultofcommitteeworkduringWorldWarI1byASAandABC(American,British,Canadian),AmericanStandard,LimitsandFitsforEngineeringandManufacturing(PartI),ASAB4.1-1947,wasproduced.TheprefacetothatdocumentmadesignificantreferencetothecontributionoftheABCmeet-ingsindevelopingagreementonfivebasicprinciples,fourofwhchapplytothepresentstandard.Theserelatedtothedesirabilityofestablishingcommondefinitions,atableofpreferredbasicsizes,asystemofpreferredtolerancesandallowances,andauniformmethodofapplyingtolerances.In1973,theGeneralMotorsCorporationrecognizedaneedforametricstandardsimilartotheIS0R286andpublishedaninterimstandardwhichwaslateradoptedasanANSISpecialMetricPublication,SR11.TheEMStandardsCommitteewasreorganizedinNovember1975,andrenamed“StandardizationofAllowancesandTolerancesforManufacturedParts”.Thefirstdraftproposalofthisstandardwasbasedontheprinciplesnotedaboveandutilizedcomputerprogramstoimplementtheconcept.ThepreferredbasicsizeshavebeenselectedfromtheAmericanNationalStandardforPreferredMetricSizesforRound,SquareandHexagonalMetalProducts,B32.4-1974,andthefirstchoicesizesareallcon-sistentlyroundedofffromtheRenard10(R10)seriesofpreferrednumbers.Alogicalreductionorexpan-sionofthefirstchoicesizescansimplybeachievedbyu...
