BSW AND BSF THREAD GAUGESGauges for testing parallel threadshaving a full form Whitworth profileare manufactured to BS 84:1956, and BS 919: Part 2: 1971.BS 84specifies basic information forthe Whitworth form, and tabulatesdiameters for threads designated BSWand BSF.BSW is a coarse thread series from 1/8”to 6” diameter.BSF is a fine thread series from 3/16” to3” diameter.Basic form Whitworth ThreadH–6rHh27.5°27.5°rH–6Pitch pH= 0.960491pH6= 0.160082p8h=23H= 0.0327pr= 0.137329pProvision is made for three classes of fitfor external threads. Close, Mediumand Free, and two classes for internalthreads. Medium and Normal.Close class applies to threads requiringa snug fit, and is only used where thereis a controlled accuracy of form andpitch. Medium class applies to betterclass interchangeable threads. Free andNormal classes apply to the majority ofcommercial quality threads.Unless otherwise specified by thecustomer, gauges for all internal andexternal product threads are made tothe basic sizes as specified in BS 84,with the exception of Medium andFree fit bolts up to and including 3/4”diameter. These have a platingallowance, the magnitude of which isdependent on diameter and pitch.BS 919: Pt 2: 1971specifies the limitsfor gauges with threads having a fullform profile.The gauge limits are dependent uponthe diameter/pitch. Generally the largerthe diameter the larger the limit,within defined bands.SCREW PLUGSSCREW RINGSCALIPERSGONOGO‘E’GONOGOROLLERKNIFEClass of fitClass of fitClass of fitClass of fitSIZEMEDMEDSTDMEDANYANY1/8” x 40 BSW028002810280A10001001192021203/16” x 24 BSW028202830282A10021003192121211/4” x 20 BSW028402850284A10051006192221225/16” x 18 BSW028602870286A10071008192321233/8” x 16 BSW 0288020288A10091010192421247/16” x 14 BSW029002910290A10111012192521251/2” x 12 BSW 029202930292A10131014192621269/16” x 12 BSW029402950294A10151016192721275/8” x 11 BSW 029602970296A10181019192821283/4” x 10 BSW029802970298A10201021192921297/8” x 9 BSW 030003010300A10221023193021301” x 8 BSW030203030302A102410251931213111/8” x 7 BSW030403050304A102610271932213211/4” x 7 BSW 030603070306A102810291933213313/8” x 6 BSW030803090308A103010311934213411/2” x 6 BSW 031003110310A10321033193521353/16” x 32 BSF025002510250A10601061190021001/4” x 26 BSF025202530252A10621063190121015/16” x 22 BSF02025502A101065190221023/8” x 20 BSF025602570256A10661067190321037/16” x 18 BSF 025802590258A10691070190421041/2” x 16 BSF026002610260A10711072190521059/16” x 16 BSF026202630262A10731074190621065/8” x 14 BSF02026502A10751076190721073/4” x 12 BSF026602670266A10771078190821087/8” x 11 BSF026802690268A10791080190921091” x 10 BSF027002710270A108110821910211011/8” x 9 BSF027202730272A108310841911211111/4” x 9 BSF027402750274A108510861912211213/8” x 8 BSF027602770276A1087101913211311/2” x 8 BSF027802790278A10109019142114The types of gauge which areCalibrationrecommended to be used are similar toServicesthose used for ISO and Unified threads,availablewith the exception that the Go plugson all ourand Go rings test the major, effectiveproducts.and minor diameters of the product0002threads (Maximum material limit). TheNot Go gauges test the effectivediameter only. BA AND G SERIES THREAD GAUGESBA SERIESBA SERIESGauges for testing threads havingSCREW PLUGSSCREW RINGSCALIPERSa full form BA profile aremanufactured to BS 93: 1951, andBS 919: Part 2: 1971.BS 93specifies basic information for theBritish Association thread form, andtabulates diameters for threads from0BA to 25BA. However, 10BA isgenerally the smallest size manufacturedSIZEGONOGO‘E’GONOGOROLLERKNIFEas stock items. (Smaller sizes may be0 BA021002110210A0920092118802080quoted for on application). 1 BA021202130212A09230924188120812 BA021402150214A0925092618822082Basic form BA Thread3 BA 021602170216A09270928188320834 BA021902200219A09290930188420845 BA 022202230222A0931093218852085S6 BA022402250224A09340935188620867 BA022702280227A093709381887208747.5°r8 BA023002310230A0939094018882088Hh23.75°23.75°9 BA 023202330232A094209431820r10 BA023402350234A0944094510209011 BA023702380237A0946-11209112 BA023902400239A0947-122092SpG SERIESGONOGO‘E’GONOGOROLLERKNIFEH = 1.136 34 xph = 0.600 00 xpSIZEABr = 0.180 83 x ps = 0.268 17 x pG1/80180N0181N0180AN0960N0961N/0962N18602060G1/40182N0183N0182AN0963N09N/0965N18612061External threads from OBA to 10BA areG3/80184N0185N0184AN0966N0967N/0968N18622062provided with an allowance of 0.001”G1/20186N0187N0186AN0969N0970N/0971N18632063on diameter to allow for easy assemblyG5/80188N01N0188AN0972N0973N/0974N1820with the internal thread. G3/40190N0191N0190AN0975N0976N/0977N18652065G7/80192N0193N0192AN0978N0979N/0980N18662066Provision is made for two classes of fitG10194N0195N0194AN0981N0982N/0983N18672067for external threads. Close and NormalG11/40196N0197N0196AN0984N0985N/0986N18682068G11/20198N0199N0198AN0987N0988N/09N18692069for sizes from OBA to 10BA inclusive,G13/40200N0201N0200AN0990N0991N/0992N18702070and for Normal class only for sizes fromG20202N0203N0202AN0993N0994N/0995N1871207111BA to 16BA. Close class is intendedfor precision parts where there isdimensions and tolerances of the productcontrolled accuracy of form and pitch.thread, and to ISO 228/2 - 1980,forThe specification states that whereNormal class is intended for generalverification by means of limit gauges. no class is specified, class B should beassumed.commercial use. The standard specifies basic informationThere is only one class of fit for internalfor Whitworth form fastening pipeInternal and external threads arethreads, which is not designated.threads, and tabulates diameters havingdesignated by the letter G followed byBS 919: Pt 2:1971specifies the limits fora thread size designation in the rangethe thread size designation. Thisgauges, and are similar in style to those1/16 to 6 inclusive. designation refers to the pipe size andused for Whitworth threads.The basic thread form is the Whitworthnot to the thread diameter. G SERIESprofile. (As shown on previous page).The gauge limits and principles areThere is no allowance provided forsimilar to the limits specified in Gauges for testing threads to external or internal threads. ISO1502, and are somewhat differentBS 2779: 1986 (G Series).Provision is made for two classes of fitto the limits for Whitworth gaugesBS 2779specifies details of pipefor external threads. Class A and Classspecified in BS 919:Pt2:1971. threads where pressure tight joints arenot required, and also specifies theB, and one class only for the internalthread, which is not designated.TheThe regular checking of gauges inlimits for gauges for testing theexternal class A tolerance is equivalentconstant use is important, andproduct thread. to the internal thread tolerance. Theshould be carried out as describedBS 2779 is technically equivalent to ISOclass B tolerance is twice that of theon previous pages.228/1 - 1982for the designation,class A tolerance. 9
