Parallel screw threads of Whitworth form

Transcription

1 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BRITISH STANDARD BS : Specifiction for Prllel screw threds of Whitworth form UDC

2 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: This British Stndrd, hving been pproved by the MechniclEngineering Industry Stndrds Committee nd endorsed by thechirmn of the Engineering Divisionl Council, ws published under the uthority of the GenerlCouncil on 2 September BSI First published s BS : nd BS 2: First revision s BS (incorporting BS 2) My 0 Second revision September The following BSI references relte to the work on this stndrd: Committee reference MEE//2 Drft for comment CT(MEE) ISBN Co-operting orgniztions The Mechnicl Engineering Industry Stndrds Committee, under whose supervision this British Stndrd ws prepred, consists of representtives from the following Government deprtments nd scientific nd industril orgniztions: Admirlty* Air Ministry* Associted Offices Technicl Committee Assocition of Consulting Engineers (Incorported) British Chemicl Plnt Mnufcturers Assocition British Compressed Air Society British Electricl nd Allied Mnufcturers Assocition* British Engineers Assocition* British Internl Combustion Engine Mnufcturers Assocition British Iron nd Steel Federtion British Rilwys, The British Trnsport Commission* Centrl Electricity Authority nd Are Bords Crown Agents for Overse Governments nd Administrtions D.S.I.R. Mechnicl Engineering Reserch Lbortory* Engineering Equipment Users Assocition* Gs Council High Commission of Indi Institute of Mrine Engineers Institute of Petroleum Institution of Civil Engineers Institution of Gs Engineers Institution of Heting nd Ventilting Engineers Institution of Mechnicl Engineers* Institution of Mechnicl Engineers (Automobile Division) Institution of Production Engineers* Locomotive nd Allied Mnufcturers Assocition* Ministry of Fuel nd Power Ministry of Lbour nd Ntionl Service (Fctory Deprtment) Ministry of Supply* Ministry of Trnsport nd Civil Avition Ministry of Works Ntionl Col Bord Ntionl Physicl Lbortory Rdio Industry Council* Wr Office The orgniztions mrked with n sterisk in the bove list, together with the following, were directly represented on the Committee entrusted with the preprtion of this stndrd: Agriculturl Engineers Assocition British Bolt, Nut, Screw nd Rivet Federtion Cut Thred Screwing Tool Mnufcturers Assocition Engineering Stndrds Co-ordinting Committee Guge nd Tool Mkers Assocition Ground Thred Tp Assocition Mchine Tool Trdes Assocition Ntionl Assocition of Mrine Engine Builders Scientific Instrument Mnufcturers Assocition Society of British Aircrft Constructors Society of Motor Mnufcturers nd Trders Ltd. Telecommuniction Engineering nd Mnufcturing Assocition Amendments issued since publiction Amd. No. Dte Comments

3 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI Contents BS: Pge Co-operting orgniztions Inside front cover Foreword iii Scope 2 Nomenclture nd definitions Form of Whitworth screw threds Clsses of bolts nd nuts Stndrd dimeter pitch series: limits nd tolernces 2 Plted threds 2 Stinless steel bolts Selected thred series ) Bsic sizes b) Design sizes c) Tolernces Tolernces on effective dimeter, pitch nd flnk ngles 0 Designtion of screw threds of Whitworth form Guges Appendix A Truncted Whitworth form threds with flt crests Appendix B Bses of tolernces nd llownces for Whitworth form screw threds Appendix C Tolernces on pitch nd ngle in reltion to tolernce on effective dimeter Appendix D Notes on the form of the crests of Whitworth threds 2 Appendix E Figure Bsic form of Whitworth thred Figure 2 Effective dimeter tolernce zones of recommended combintions of clsses of bolts nd nuts hving Whitworth screw threds Figure Tolernce zones for close clss bolt nd medium clss nut / in. B.S.W. ( t.p.i.) illustrted Figure Tolernce zones for medium clss bolt with llownce nd norml clss nut. / in. B.S.W. ( t.p.i.) illustrted Figure Tolernce zones for free clss bolt with llownce nd norml clss nut. / in. B.S.W. ( t.p.i.) illustrted 0 Figure Effective dimeter tolernce zones for Whitworth bolts nd nuts, unplted or before plting, nd fter plting (cf.figure 2) of sizes / in. nominl size nd smller Figure Tolernce zones for truncted Whitworth thred / in. B.S.W. ( t.p.i.) illustrted Figure Crest forms resulting from different production methods Tble Bsic sizes 2 Tble 2 Bolts Close clss Tble Nuts Medium clss Tble Bolts Medium clss ) Nominl sizes up to nd including / in. b) Nominl sizes bove / in. Tble Nuts Norml clss BSI i

4 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Pge Tble Bolts Free clss ) Nominl sizes up to nd including / in. b) Nominl sizes bove / in. Tble Bsic sizes Tble Bolts Close clss Tble Nuts Medium clss Tble 0 Bolts Medium clss 2 ) Nominl sizes up to nd including / in. b) Nominl sizes bove / in. Tble Nuts Norml clss 22 Tble 2 Bolts Free clss 2 ) Nominl sizes up to nd including / in. b) Nominl sizes bove / in. Tble Preferred dimeters nd pitches Frctionl sizes 2 Tble Preferred dimeters nd pitches Deciml sizes 2 Tble Depths of thred for vrious pitches 2 Tble Bolts Medium nd free clss llownces Tble Bolts Close clss Tble Nuts Medium clss 2 Tble Bolts Medium clss 2 Tble Nuts Norml clss Tble Bolts Free clss Tble 2 Bsic dt Tble 22 Bolts nd nuts ll clsses Tble 2 Bolts nd nuts ll clsses Tble 2 Nuts Close clss Tble 2 Nuts Close clss Tble 2 Nuts Close clss ii BSI 02-00

5 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI Foreword This stndrd mkes reference to the following British Stndrds: BS, Screw guge limits nd tolernces. BS, Tpping drill sizes. BS, Pt. 2. Guide to the selection of fits. BS 2, Definitions for use in mechnicl engineering. BS : This revised British Stndrd hs been prepred, under the uthority of the Mechnicl Engineering Industry Stndrds Committee, to supersede BS:0, Screw threds of Whitworth form. It pplies to threds of Whitworth form used for generl engineering purposes nd is not intended to pply to specil pplictions such s those requiring interference fits. The stndrd includes tbles of bsic sizes, limits nd tolernces for British Stndrd Whitworth (B.S.W.) nd British Stndrd Fine (B.S.F.) screw threds. In ddition it now provides Selected Thred series of recommended dimeter-pitch combintions for use in pplictions where the stndrd corse (B.S.W.) nd fine (B.S.F.) pitch series hve insufficiently fine pitches. The British Stndrd Pipe prllel thred series ws incorported in BS:0 s fine thred series for generl engineering purposes, nd though this series ws not intended for pipe joints it hs been extensively used on certin types of pipe fittings, such s unions, compression type connections, etc., where the pressure sel is not mde on the threds. This hs cused some confusion with the pipe threds specified in BS2 ) where the pressure sel is, in fct, mde on the threds. It hs, therefore, been decided to publish the tbles of bsic sizes, limits nd tolernces for the British Stndrd Pipe prllel thred series given in BS:0 in new stndrd, BS 2, Fstening Threds of B.S.P. Sizes, now in course of preprtion. This stndrd, in ddition to BS 2, which is now being revised, will come under the egis of the Pipe Threds Committee of BSI nd these two stndrds will then include recommended limits nd tolernces for ll B.S.P. threds whether or not the pressure sel is mde upon the threds. The new Selected Thred series will, in most cses, be more suitble for use in new designs thn the BS Pipe prllel thred series in cses where n extr fine pitch thred is required, nd its use is strongly recommended. In revising this stndrd, dvntge hs been tken of the experience gined in the use of BS :0, to modify it to conform to modern thred tolerncing prctice. Thus n llownce (minimum clernce) is provided on certin clsses of bolts of sizes up to nd including / in. dimeter; the recommended ssocitions of clsses of bolts nd nuts include nuts hving lrger effective dimeter tolernces thn the corresponding sizes of bolts. Three clsses of tolernce re provided for bolts, the Close, Medium nd Free Clsses, equivlent to the old Close, Medium nd Free Fit bolts. The llownce is provided on bolts in the Medium nd Free Clsses by reducing the mximum bolt limits below bsic size. The purpose of this llownce is to provide for the threds to be plted if necessry, the plting encroching within the llownce; it lso gurntees esy ssembly of mximum metl bolts nd nuts, thus fcilitting the use of torque wrenches. Two clsses of tolernce for nuts re recommended, Medium Clss nd Norml Clss, identicl with the old Medium nd Free Fit nuts respectively. The old Close Fit (now termed Close Clss) nuts, re now regrded s non-preferred but, in view of their usge in the pst nd for specil needs, their limits nd tolernces re given in n Appendix to the stndrd. All screw threds mde in ccordnce with this revised stndrd will ssemble with the corresponding nominl sizes of mting screw threds mde to BS:0. ) BS2, Pipe threds. BSI iii

6 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: It will be observed tht no chnge hs been mde in the generl three-prt formul used s bsis for tolerncing effective dimeters, nd the formule used for tolerncing the other thred elements lso remin unchnged from those in BS:0; the reson for this is to minimize ny chnges in the sizes of the guges used to control the size of the finished work. The tble of recommended dimeter-pitch combintions for screw threds in the Selected Thred series follows very closely the corresponding Tble in BS 0, Unified Screw Threds. In revising the stndrd the following mendments issued subsequent to BS:0 hve been incorported in the text, with the exception of tht prt of the mendments deling with B.S.P. threds, nd Amendments Nos. nd 2 hve been restricted to lengths of enggement of bolt nd nut up to pitches. Amendment No., June 2, provided simplified tbles of tolernces for threds not in the three stndrd dimeter-pitch series (B.S.W., B.S.F. nd B.S.P.), bsed on length of enggement of bolt nd nut of 0pitches, but pplicble in prctice to ll resonble lengths of enggement. Amendment No. 2, April, specified tht the tolernces given in the three stndrd dimeter-pitch series should pply to ll lengths of enggement. Amendment No., August, provided informtion bout truncted Whitworth form screw threds. Amendment No., December, gve extensions of tbles of limits nd tolernces for the lrger sizes of stndrd dimeter-pitch combintions of Whitworth form. In conclusion it my be sked why the revision of this stndrd hs been undertken in view of the stndrdiztion of the Unified thred in BS 0. The reson is tht Whitworth threds will undoubtedly continue to be used for mny yers, especilly on replcements or spre prts. A British Stndrd does not purport to include ll the necessry provisions of contrct. Users of British Stndrds re responsible for their correct ppliction. Complince with British Stndrd does not of itself confer immunity from legl obligtions. Summry of pges This document comprises front cover, n inside front cover, pges i to iv, pges to nd bck cover. This stndrd hs been updted (see copyright dte) nd my hve hd mendments incorported. This will be indicted in the mendment tble on the inside front cover. iv BSI 02-00

7 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI Scope BS: This British Stndrd reltes to prllel screw threds, hving the Whitworth form of thred, used for generl engineering purposes. It is not intended to pply to threded pipe joints, screw threds ssocited with interference fits, such s those on the metl-ends of studs nd in the corresponding tpped holes, or to screw threds which re subject to high temperture. This stndrd includes: ) A corse thred series, the British Stndrd Whitworth (B.S.W.) Series, from / in. to in. dimeter. b) A fine thred series, the British Stndrd Fine (B.S.F.) Series, from / in. to / in. dimeter. NOTE The tbles of limits nd tolernces in the B.S.F. Series extend up to the in. size only, since nominl sizes bove in. re rrely used. c) A supplementry Selected Thred Series from / in. dimeter upwrds. d) Screw threds of Truncted Whitworth form (Appendix A). Supplementry informtion is given in Appendix A to Appendix E. 2 Nomenclture nd definitions For the nomenclture nd definitions of terms used in this stndrd, see BS 2, Definitions for use in Mechnicl Engineering. Form of Whitworth screw thred The bsic (nd design) form of the Whitworth thred is shown in Figure. It is symmetricl V-thred in which the ngle between the flnks, mesured in n xil plne, is ; one-sixth of the shrp vee is truncted t top nd bottom, the thred being rounded eqully t crests nd roots by circulr rcs blending tngentilly with the flnks, the theoreticl depth of thred being thus 0.02times the nominl pitch. The bsic thred depths clculted from the bove definition re rounded off to the nerest in. Clsses of bolts nd nuts Three clsses of tolernces for bolts nd two clsses for nuts 2) re provided s follows: Close clss bolts. The close clss ) pplies to screw threds requiring fine snug fit, obtinble consistently only by the use of the highest qulity production equipment supported by prticulrly efficient system of guging nd inspection. It should be used only for specil work where refined ccurcy of pitch nd thred form re prticulrly required. Medium clss bolts nd nuts. The medium clss pplies to the better clss of ordinry interchngeble screw threds. Free clss bolts. The free clss pplies to the mjority of bolts of ordinry commercil qulity. Norml clss nuts. The norml clss pplies to ordinry commercil qulity nuts; this clss is intended for use with medium or free clss bolts. The reltive mgnitudes nd dispositions of the effective dimeter tolernce zones ) for the recommended combintions of clsses re shown in Figure 2. It will be noted tht the lower limit of the nut is lwys bsic size. No llownce is provided for close clss bolts, but for medium nd free clss bolts n llownce is provided between the lower limit for the nut (bsic size) nd the upper limit for the bolt on sizes / in. nominl dimeter nd below. The llownce mounts to 0. medium clss bolt effective dimeter tolernce for nominl sizes of / in. down to / in. The llownce for nominl sizes less thn / in. is the sme s tht for the / in. size. Since it is more difficult to control the threding of nuts thn bolts the recommended clsses of nuts to be ssocited with close nd medium clss bolts hve effective dimeter tolernces 0 per cent greter thn those of the ssocited bolts. 2) The terms bolts nd nuts re used in generl sense to designte externl nd internl threds respectively. ) Limits nd tolernces for close nuts re given in Appendix E. ) For the bses of the tolernces nd llownces see Appendix B. BSI 02-00

8 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: The choice of fit for prticulr purpose rests with the designer. A close clss bolt would usully be ssembled with medium clss nut, nd medium or free clss bolt with norml clss nut, but in specil circumstnces different combintions of clsses my be specified for mting bolts nd nuts if desired. Informtion bout plting, s pplied to the vrious clsses of bolts nd nuts, is given in Cluse. Stndrd dimeter pitch series: Limits nd tolernces The bsic sizes for the B.S.W. nd B.S.F. series re given in Tble nd Tble respectively. Limits nd tolernces for the mjor, effective nd minor dimeters for the vrious clsses re given in Tble 2 to Tble for the B.S.W. series nd in Tble totble 2 for the B.S.F. series. Limits nd tolernces for close clss nuts in the B.S.W. nd B.S.F. series re given in Appendix E. In these tbles, the effective dimeter tolernces, which re intended to include the dimetrl effects of pitch nd ngle error (see Appendix C), hve been clculted from the generl formul (see pge0) tking the length of enggement s being equl to the nominl dimeter of the thred. In order to reduce to minimum the number of NOT GO guges required, the tolernces for the B.S.W. nd B.S.F. series of threds, lthough clculted for the lengths of enggement just quoted my, however, be regrded s pplicble to lengths of enggement up to fifteen pitches. The tolernces quoted for the mjor nd minor dimeters of threds belonging to the B.S.W. nd B.S.F. series my be ccepted for ny length of enggement. Following existing prctice, no tolernce is specified for the mjor dimeters of the nuts, but only minimum size, which is the sme s the bsic mjor dimeter. The mjor dimeters of nuts will be controlled in prctice by the mjor dimeters of the tps or other screwing tools used to cut the threds. Figure, Figure nd Figure show, for the three recommended combintions of clsses respectively, the reltionship existing between the dimetrl tolernces for / in. B.S.W. bolt nd nut. It will be noted tht the nut minor dimeter tolernces re such s to permit tpping drill of mple size to be used, thus preventing binding t the root of the tp during the tpping opertion. If full dvntge is tken of the generous nut minor dimeter tolernces, the crests of the nut threds will be flt. In specil cses, though, where thin nuts re used, it my be desirble not to tke full dvntge of the tolernce on minor dimeter. It will lso be noted tht the bolt mjor dimeter tolernces re such s to permit crests which re not perfectly rdiused (seeappendix D). Formule for clculting the tolernces for mjor, effective nd minor dimeters re given in Appendix B. Plted threds The following recommendtions refer to the limits for screw threds which re plted with metls such s cdmium, nickel, tin or zinc, where the usul thickness of plting is of the order of in.; they do not pply to hevily plted threds. Tking s bsis Figure 2, which shows the effective dimeter tolernce zones for bolts nd nuts of the vrious clsses supplied unplted, Figure shows in ddition the corresponding recommended tolernce zones for bolts nd nuts of nominl sizes / in. nd below before nd fter plting. It will be noted for these sizes tht plting is ccommodted within the llownce in the cse of the medium nd free clss bolts, nd by djustment of the bolt tolernce zone in the cse of the close clss bolts. The interprettion of Figure is s follows: i) Both free nd medium clss bolts re suitble for plting. The finished size of the screw threds fter plting shll not exceed the bsic size. ii) Should it be necessry to plte close clss bolts, gin the finished size of the threds fter plting shll not exceed the bsic size. In order to void ny undue restriction of the tolernce for screwing, the sizes of close clss bolts before plting my be smller thn the lower limits specified in Tble 2 nd Tble by n mount not greter thn 0.00 in. iii) The sizes of finished medium clss nd norml clss nuts, whether plted or not, shll not fll below the lower limits specified in the pproprite tbles of limits nd tolernces. iv) Since the plting of medium clss nuts my necessitte reduction in the mnufcturing tolernces in order tht, fter plting, they comply with the specified lower limits, it is strongly recommended tht plted norml clss nuts be used insted of medium clss where plting is requirement. 2 BSI 02-00

9 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Bolts nd nuts of nominl sizes bove / in., whether plted or not, shll comply with the limiting sizes specified in the pproprite tbles with the following exception. In order to void ny undue restriction of the tolernce for screwing, the sizes of close clss bolts before plting my be smller thn the lower limits specified in the tbles by n mount not greter thn 0.00in. Where it is known tht nuts will be plted, cre should be tken tht the nuts re mde with minimum sizes slightly greter thn bsic size in order to effect stisfctory ssembly fter plting. Similrly, medium nd free clss bolts of nominl sizes bove / in. dimeter, which re required to be plted, should be mde with mximum sizes slightly less thn bsic size. The bove remrks pply not only to the tolernce zones for effective dimeter, but eqully to the tolernce zones for the mjor nd minor dimeters of plted threds. The limiting sizes of medium nd free clss B.S.W. nd B.S.F. bolt threds before nd fter plting re indicted in Tble, Tble, Tble 0 nd Tble 2 respectively. Recommendtions on the guging of plted screw threds re given in n Appendix to BS, Screw guge limits nd tolernces. Stinless steel bolts Owing to the tendency for close-fitting bolts nd nuts of stinless steel to seize when tightened together, it is recommended tht stinless steel bolts of nominl sizes / in. nd below should not be mde to close clss limits but rther to medium or free clss limits for unplted bolts. It is recommended tht stinless steel bolts of nominl sizes bove / in. shll hve mximum nd minimum limits which re 0.00in. smller thn the vlues obtined from the tbles. Selected thred series Recommended dimeter-pitch combintions for the pplictions of threds of Whitworth form, for which the B.S.W. nd B.S.F. dimeter-pitch series re unsuitble, re given in Tble nd Tble A. Two tbles of preferred dimeters nd ssocited pitches re included to meet the needs of different sections of industry, some preferring to use common frctions nd others decimls. Tble lists the frctionl, nd Tble A the deciml series. It will be noted tht both tbles contin, bove / 2 in. dimeter, the sme / in. nd / 2 in. steps, the difference between the two tbles being tht in the deciml series the intermedite / in. steps hve been replced by steps to the nerest / 0 in. dimension. This enbles the sme dimeters to be used s re recommended in BS-2 ). ) Bsic sizes. The bsic effective nd minor dimeters my be determined by subtrcting from the bsic mjor dimeter the bsic depth of thred nd twice the bsic depth of thred respectively (Columns nd, Tble ). b) Design sizes. i) Nuts. The design sizes of the mjor, effective nd minor dimeters for ll clsses re the sme s the corresponding bsic sizes. ii) Bolts. A. Close clss. The design sizes re the sme s the bsic sizes. B. Medium nd free clsses. Bsic mjor dimeters of / in. nd below. The design sizes re obtined from the bsic sizes by subtrcting the pproprite llownce given in Tble. Bsic mjor dimeters bove / in. The design sizes re the sme s the bsic sizes. c) Tolernces. The tolernces on Whitworth Selected Threds for bolts nd nuts of nominl sizes up toin. re obtined from Tble to Tble inclusive. For nominl dimeters bove in. the tolernces should be clculted from the dt nd formule in Appendix B. The effective dimeter tolernces hve been clculted from the generl formul given in Appendix B, ssuming length of enggement of the mting threds equl to ten times the pitch. The tolernces so obtined my be regrded s stisfctory for ll norml lengths of enggement, sy five to fifteen pitches. For exceptionl lengths of enggement, if these tolernces re found to be unsuitble, the effective dimeter tolernce should be clculted from the bsic formul in Appendix B, giving L e its ctul vlue. ) BS-2, Guide to the selection of fits. BSI 02-00

10 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: No tolernce is specified for the mjor dimeter of the nut thred, s it is considered tht this dimension will be controlled dequtely by the crests of the tps or other cutting tools used to produce the threds. All dimetrl tolernces on screw threds re pplied unilterlly from the pproprite design size of the dimension, minus for bolt nd plus for nut. Exmples illustrting the use of Tble to Tble when determining limits nd tolernces of Whitworth Selected Screw Threds re given following Tble. Exceptionl design requirements my, t times, necessitte the use of screw thred of Whitworth form but hving dimeter-pitch combintion differing from those recommended in Tble nd Tble A nd the relevnt notes. It is recommended in such cses tht the number of threds per inch should be chosen from the following series threds per inch The numbers of threds per inch in hevy type re to be regrded s preferred. The design sizes nd tolernces for such threds should be derived s stted for threds in the Selected Thred series. Tolernces on effective dimeter, pitch nd flnk ngles Errors in the pitch nd flnk ngles of thred virtully increse the effective dimeter of bolt nd decrese the effective dimeter of nut. The minimum metl limits stted in the tbles pply to the simple effective dimeter (s mesured long the pitch line of the thred) nd the mximum metl limits pply to the effective dimeter s virtully incresed (for bolts) or decresed (for nuts) by the dimetrl equivlents of ny errors present in the flnk ngles nd in the pitch over the length of enggement (see Appendix C). 0 Designtion of screw threds of Whitworth form It is recommended tht the following system should be dopted on drwings nd relted documents for designting the screw threds covered by the present stndrd. British Stndrd Whitworth series British Stndrd Fine series The bsic mjor dimeter of the thred nd the number of threds per inch should be dded to the designtion. If the thred is left-hnd the symbol LH should follow the designtion. Exmples: / in. B.S.W. / 2 in. B.S.F., LH For screw threds of the selected dimeters nd pitches given in Tble nd Tble A, the bsic mjor dimeter nd number of threds per inch should be stted, followed by the symbol Whit. S. Exmple: in. Whit. S. Screw threds of Whitworth form but not hving the selected dimeter-pitch combintions given in Tble nd Tble A should be designted s given below: Exmple: 0. in. Whit. Where it is desired to designte the clss of thred tolernce, one of the four terms close, medium, free or norml should be dded in brckets, together with the word bolt or nut s pproprite. Exmples: / in. B.S.W. (close) bolt. in. Whit. S. (free) bolt. / 2 in. B.S.F. (norml) nut. Designtion B.S.W. B.S.F. It is recommended tht multiple-strt Whitworth form threds should be designted s in the following exmple: 2 in. 2 strt, 0.2in. led, 0. in. pitch, Whit. BSI 02-00

11 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI Guges BS: It is recommended tht the guging system to be employed for checking screw threds of Whitworth form between the limits lid down in this stndrd should be tht given in BS, Screw guge limits nd tolernces. Unless otherwise stted GO ring or clliper guges for medium or free clss bolts of nominl sizes / in. nd below will be supplied mde to the limits for unplted bolts. BSI 02-00

12 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BSI Figure Bsic form of Whitworth thred BS :

13 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BSI NOTE The Medium Clss bolt effective dimeter tolernce is shown s 00 units nd the other vlues re expressed s percentge of this tolernce. The formul for effective dimeter tolernce is given in Appendix B. NOTE 2 See Appendix E for Close Clss nuts for specil needs. * See Cluse. Figure 2 Effective dimeter tolernce zones of recommended combintions of clsses of bolts nd nuts hving Whitworth screw threds BS :

14 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Figure Tolernce zones for close clss bolt nd medium clss nut / in. B.S.W. ( t.p.i.) illustrted BSI 02-00

15 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI NOTE The mximum bolt dimensions refer to unplted bolts only. BS: Figure Tolernce zones for medium clss bolt with llownce nd norml clss nut. / in. B.S.W. ( t.p.i.) illustrted BSI 02-00

16 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: NOTE The mximum bolt dimensions refer to unplted bolts only. Figure Tolernce zones for free clss bolt with llownce nd norml clss nut. / in. B.S.W. ( t.p.i.) illustrted 0 BSI 02-00

17 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BSI NOTE NOTE 2 Bolt Medium Clss effective dimeter tolernce is shown s 00 units. See Appendix E for Close Clss nuts for specil needs. Figure Effective dimeter tolernce zones for Whitworth bolts nd nuts, unplted or before plting, nd fter plting (cf. Figure 2) of sizes / in. nominl size nd smller BS :

18 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Corse thred series, B.S.W. Tble Bsic sizes 2 Nominl size Number of threds per inch Pitch Depth of thred Mjor dimeter Effective dimeter Minor dimeter Cross sectionl re t bottom of thred in. in. in. in. in. in. sq. in. b / / 0 2 / / / / / 2 / 2 2 / / / 0 / / / / 2 / 2 2 / 2 / 2 2 / / / 2 / / 2 / To be dispensed with wherever possible. b Dimensionlly, the / in. 0 t.p.i. thred belongs more ppropritely to the B.S.F. series, but it hs for so long been ssocited with the B.S.W. series tht it is now included herein. 2 BSI 02-00

19 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI Tble 2 Bolts Close clss BS: Limits nd Tolernces 2 0 Nominl size Number of threds per in. Mjor dimeter Effective dimeter Minor dimeter Mx. Tol. Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. in. in. / / 0 2 / / / / / 2 / 2 2 / / / 0 / / / / 2 / 2 2 / 2 / 2 2 / / / 2 / / 2 / To be dispensed with wherever possible BSI 02-00

20 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Tble Nuts Medium clss Limits nd Tolernces 2 Nominl size Number of threds per inch Mjor dimeter Effective dimeter Minor dimeter Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. / / 0 2 / / / / / 2 / 2 2 / / / 0 / / / / 2 / 2 2 / 2 / 2 2 / / / 2 / / 2 / To be dispensed with wherever possible BSI 02-00

21 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI ) Nominl sizes up to nd including / in. Tble Bolts Medium clss BS: Limits nd Tolernces Nominl size Number of threds per inch Mjor dimeter Effective dimeter Minor dimeter Unplted or before plting After plting Unplted or before plting After plting Unplted or before plting After plting Mx. Tol. Min. Mx. Mx. Tol. Min. Mx. Mx. Tol. Min. Mx. in. in. in. in. in. in. in. in. in. in. in. in. in. / / 0 2 / / / / / 2 / 2 2 / / / b) Nominl sizes bove / in Nominl size / / / / 2 / 2 2 / 2 / 2 2 / / / 2 / / 2 / 2 Number of threds per in. Mjor dimeter Effective dimeter Minor dimeter Mx. Tol. Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. in. in To be dispensed with wherever possible BSI 02-00

22 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Tble Nuts Norml clss Limits nd Tolernces 2 Nominl size Number of threds per inch Mjor dimeter Effective dimeter Minor dimeter Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. / / / 0 2 / / / / 2 / 2 2 / / / / 0 / / / 2 / 2 2 / 2 / 2 2 / / / 2 / / 2 / To be dispensed with wherever possible BSI 02-00

23 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI ) Nominl sizes up to nd including / in. Tble Bolts Free clss BS: Limits nd Tolernces Nominl size Number of threds per inch Mjor dimeter Effective dimeter Minor dimeter Unplted or before plting After plting Unplted or before plting After plting Unplted or before plting After plting Mx. Tol. Min. Mx. Mx. Tol. Min. Mx. Mx. Tol. Min. Mx. in. in. in. in. in. in. in. in. in. in. in. in. in. / / 0 2 / / / / / 2 / 2 2 / / / b) Nominl sizes bove / in Nominl size / / / / 2 / 2 2 / 2 / 2 2 / / / 2 / / 2 / 2 Number of threds per in. Mjor dimeter Effective dimeter Minor dimeter Mx. Tol. Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. in. in To be dispensed with wherever possible BSI 02-00

24 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Fine thred series, B.S.F. Tble Bsic sizes 2 Nominl size Number of threds per inch Pitch Depth of thred Mjor dimeter Effective dimeter Minor dimeter Cross sectionl re t bottom of thred in. in. in. in. in. in. sq. in. b / / / 2 / 2 / 2 22 / / / / 2 / / / 2 / / / / / 2 / / 2 2 / 2 / 2 2 / / / 2 / / NOTE It is recommended tht for lrger dimeters in this series four threds per inch be used. To be dispensed with wherever possible. b The use of 2 B.A. threds is recommended in plce of / in. B.S.F BSI 02-00

25 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI Tble Bolts Close clss BS: Limits nd Tolernces 2 0 Nominl size Number of threds per in. Mjor dimeter Effective dimeter Minor dimeter Mx. Tol. Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. in. in. b / / / 2 / 2 / 2 22 / / / 2 / / / / 2 / / / / / 2 / / 2 2 / 2 / 2 2 / To be dispensed with wherever possible. b The use of 2 B.A. threds is recommended in plce of / in. B.S.F BSI 02-00

26 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Tble Nuts Medium clss Limits nd Tolernces 2 Nominl size Number of threds per inch Mjor dimeter Effective dimeter Minor dimeter Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. b / / / 2 / 2 / 2 22 / / / / 2 / / / 2 / / / / / 2 / / 2 2 / 2 / 2 2 / To be dispensed with wherever possible. b The use of 2 B.A. threds is recommended in plce of / in. B.S.F BSI 02-00

27 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI ) Nominl sizes up to nd including / in. Nominl size Tble 0 Bolts Medium clss BS: Limits nd Tolernces Number of threds per inch Mjor dimeter Effective dimeter Minor dimeter Unplted or before plting After plting Unplted or before plting After plting Unplted or before plting After plting Mx. Tol. Min. Mx. Mx. Tol. Min. Mx. Mx. Tol. Min. Mx. in. in. in. in. in. in. in. in. in. in. in. in. in. b / / / 2 / 2 / 2 22 / / / / 2 / / / b) Nominl sizes bove / in Nominl size / / / / / 2 / / 2 2 / 2 / 2 2 / Number of threds per in. Mjor dimeter Effective dimeter Minor dimeter Mx. Tol. Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. in. in To be dispensed with wherever possible. b The use of 2 B.A. threds is recommended in plce of / in. B.S.F BSI

28 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Tble Nuts Norml clss Limits nd Tolernces 2 Nominl size Number of threds per inch Mjor dimeter Effective dimeter Minor dimeter Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. b / 2 / 2 2 / 2 / 2 2 / 22 / / / 2 / / / / 2 / / / / / /. / / / / To be dispensed with wherever possible. b The use of 2 B.A. threds is recommended in plce of / in. B.S.F BSI 02-00

29 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI ) Nominl sizes up to nd including / in. Tble 2 Bolts Free clss Introductory notes to Tble Selected thred series Frctionl sizes Preferred dimeters BS: It is strongly recommended tht the preferred dimeters should be used nd, whenever the design permits, st choice dimeter be selected. In n extreme cse, when even the 2nd choice dimeters cnnot be utilized, suitble rd choice dimeter should be selected s follows: ) Up to / 2 in.: the nerest / 2 in. size. b) Above / 2 in. nd up to in.: the nerest / in. size. c) Above in.: the nerest / in. size. Limits nd Tolernces Nominl size Number of threds per inch Mjor dimeter Effective dimeter Minor dimeter Unplted or before plting After plting Unplted or before plting After plting Unplted or before plting After plting Mx. Tol. Min. Mx. Mx. Tol. Min. Mx. Mx. Tol. Min. Mx. in. in. in. in. in. in. in. in. in. in. in. in. in. / b / / 2 / 2 / 2 22 / / / / 2 / / / b) Nominl sizes bove / in Nominl size / / / / / 2 / / 2 2 / 2 / 2 2 / Number of threds per in. Mjor dimeter Effective dimeter Minor dimeter Mx. Tol. Min. Mx. Tol. Min. Mx. Tol. Min. in. in. in. in. in. in. in. in. in. in To be dispensed with wherever possible. b The use of 2 B.A. threds is recommended in plce of / in. B.S.F BSI

30 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Before selecting rd choice dimeter, cre should be tken to scertin whether st choice or 2nd choice in the lterntive tble of the deciml series could not be used insted. 2 Preferred pitches The corsest pitch suitble to the design should normlly be used. Those pitches in brckets re included to meet less usul design requirements, nd their generl use should be voided. However, in some specilized brnches of design, prticulr pitches my be very commonly required nd it my then be desirble to tret those most commonly required s st choice pitches irrespective of the preference indicted bove. Extr fine pitches These recommendtions do not pply to extr fine pitches such s occur on thin-wlled designs. Selected thred series, Whit. S Tble Preferred dimeters nd pitches Frctionl sizes Preferred bsic mjor dimeters st choice / in. / / / / 2 / / / / / / / 2nd choice in. / / / / / / Stndrd pitches (t.p.i.) B.S.W. series / B.S.F. series Preferred pitches (t.p.i.) BSI () () () () () () () () () () () () () (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) 2 2 2

31 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI Tble Preferred dimeters nd pitches Frctionl sizes BS: Preferred bsic mjor dimeters st choice / 2 / 2 2 / 2 / 2 2 / / / 2 / in. 2nd choice in. / / 2 / 2 / 2 / 2 / / / / / Stndrd pitches (t.p.i.) B.S.W. series / 2 / 2 / 2 / / B.S.F. series / 2 / 2 / 2 Preferred pitches (t.p.i.) BSI () (2) (2) (2) (2) (2) (2) (2) (2) () () () () () () () () () (2) (2) (2) (2) (2)

32 Licensed Copy: London South Bnk University, London South Bnk University, Fri Oct 2 0:2: GMT+00:00 0, Uncontrolled Copy, (c) BSI BS: Tble Preferred dimeters nd pitches Frctionl sizes Preferred bsic mjor dimeters st choice in. / / 2 / / / 2 / / 2 2nd choice in. / / / / / / / / / / Introductory notes to Tble A Selected thred series Deciml sizes Preferred dimeters It is strongly recommended tht the preferred dimeters should be used nd tht, whenever the design permits, st choice dimeter be selected. In n extreme cse, when even the 2nd choice dimeters cnnot be utilized, suitble rd choice dimeter should be selected s follows: ) From.in. to in.: select from the non-preferred 0. in. sizes, such s 2.2, 2., 2. nd 2.. Should these prove unsuitble, choose the nerest 0.0in. dimeter. b) From in. to in.: select from the four 0. in. sizes similr to those shown in the tble for the 2nd choice below in. Only s lst resort should the non-preferred 0.in. sizes such s.2,.,. nd. be used. Before selecting rd choice dimeter, cre should be tken to scertin whether st choice or 2nd choice in the lterntive tble of the frctionl series could not be used insted. 2 Preferred pitches Stndrd pitches (t.p.i.) B.S.W. series 2 / 2 / 2 / 2 / 2 B.S.F. series Preferred pitches (t.p.i.) The corsest pitch suitble to the design should normlly be used. Those pitches in brckets re included to meet less usul design requirements nd their generl use should be voided. However, in some specilized brnches of design, prticulr pitches my be very commonly required, nd it my then be desirble to tret those most commonly required s st choice pitches irrespective of the preference indicted bove. 2 BSI (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) NOTE Lrger dimeters hve the sme preferred dimeter steps nd the sme preferred pitches s for the rnge.0 to.0 inches. (2) 2