Hi list members, In my experience British threads are as follows; Whitwo rth, a quite coarse thread, never found on bicycles, frequently used on Bri tish motorcycles where a stud threads into a aluminium casting. B.S.F. B ritish fine , the fine thread companion to Whitworth. also not often used o n bicycles. British cycle thread, a unique series of thread, almost always 26 tpi.regardless of thread diameter. Used on many British bicycles and m otorcycles down to 1/4 in. size. The BA series of threads;used for machine screws, less than 1/4 down to practically watchmakers sizes. Mudguard boss threading are as far as I know BA thread. Hex head size is often the "wh itworth size " for the given diameter of bolt {derived from a universal Whi tworth formula}, this does not mean the thread is Whitworth, just the hex s ize of the bolt head. Confused yet? It's taken me 35 years of working with British machinery ; large marine diesels to Smiths clocks ,to realize to never to jump to a thread conclusion. Use a thread gauge and a good thread reference , Machinery's handbook for example. Greg Lone Langley B.C. Canada
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