British Thread Gages

Thread Check Inc., offers a wide range of British pipe thread gages and British Whitworth thread form gages.

British thread gauges include British Standard Pipe Taper thread plug and thread ring gauges from 1/16 to 6.0”. BS-21 specifies requirements of British pipe threads for joints made pressure tight by mating of threads and are taper external, taper internal, and parallel internal. The Whitworth pipe screw thread form was redefined in ISO 7-1 1984. BS-21 and ISO 7/1 and 7/2 1984 are technically equivalent. The gages were changed in ISO 7/2 2000 and is now different than BS-21. The product threads remain the same. The latest standard to come about is under EN 10226 - 1 2004 and EN 10226 - 2 2006. The thread gage standard covered under EN 10226 - 3 is now technically equivalent to ISO 7/2 2000.

British parallel pipe thread gauges are manufactured per ISO 228 and BS - 2779. In March 2003 the British Standards Institute withdrew BS‐2779 and replaced it with ISO-228. ISO 228 - 1 which details pipe threads where pressure‐tight joints are not made on the threads. ISO 228 - 2 covers the limit gages for British pipe threads where pressure‐tight joints are not made on the threads. ISO 1179 specifies pipe connection, threaded to ISO 228-1 and gauged with ISO 228 - 2 gauges for plain end steel and other metal tubes in industrial applications. BSPP Thread gages have a 55 degree thread profile. The specification covers several go and several no go gauges designed to verify different elements of the thread. The threaded go gages ensure that the profile of the machined piece does not exceed the maximum of material provided for by the tolerances applied to the dimensions of the profile defined by ISO 228-1. The threaded no go gauges for the threads of the pieces fix the minimum material limit on the flanks of the thread. Thread Check offers both the full form style as called out in the ISO specification as well as a modified version manufactured in the U.S.A. For internal threads and thread plug gages, one class of tolerance on the pitch diameter is provided.

The British Standard Coarse Screw thread (BSW thread) is known as a parallel screw thread of Whitworth form having a 55 degree included angle. With the standardization of Unified threads, the BSW Whitworth thread form is typically being utilized for replacement parts. Steel bolts of ¾ inch and below should not be made to close class limits and instead should be specified to medium class and free class limits. Close class threads should be applied to screw threads requiring a tight fit. The better and more practical class is a medium class of fit which provides a more functional interchangeable screw thread. Free Class bolts apply to the majority of bolts of commercial grade quality. Normal class nuts are applied to commercial quality nuts and are intended for use with medium or free class bolts. Thread Check Inc., supplies both BSW thread ring gages and BSW thread plug gages from 1/8 to 6.0 inches.

The British Standard Fine Screw thread is known as a parallel screw thread of Whitworth form having a 55 degree included angle. With the standardization of Unified threads, the BSF Whitworth thread form is typically being utilized for replacement parts. Steel bolts of ¾ inch and below should not be made to close class limits and instead should be specified to medium class and free class limits. Close class threads should be applied to screw threads requiring a tight fit. The better and more practical class is a medium class of fit which provides a more functional interchangeable screw thread. Free Class bolts apply to the majority of bolts of commercial grade quality. Normal class nuts are applied to commercial quality nuts and are intended for use with medium or free class bolts. Thread Check Inc. can supply BSF thread plug and thread ring gages from 3/16 to 4 inches.

The British Association (BA) standard thread form is recommended by the British Standards Institute for screws smaller than 1/4 instead of BSW and BSF threads. BA threads are similar to Whitworth threads in terms of rounded crests and roots except that the symmetrical angles are 47 degrees and 30 minutes and the crest and root radiuses are proportionately larger. This thread system was first developed in Switzerland as a standard for small components in clocks and watches. It is sometimes referred to as the Swiss small screw thread standard. Use of the BA thread in the United States is limited to small tools typically for export. Thread Check Inc. offers BA thread plug gages in sizes from BA 0 - BA 16.

British Association - BA thread plug gages and thread ring gages conform to S.93. Tolerances are to BS.919 Part 2 2007. BA screw thread plug gages are manufactured to standard class. BA screw thread ring gages are manufactured to nominal class. All BA thread gages are right hand only.

Thread Check’s expert sales engineer can assist you with selecting the correct British thread gages for your application.