Very interesting observation that suddenly had me thinking.. there was a close relationship between BSA cycle threads and their gun threads. The standard BSA bottom bracket cycle thread was / is 24tpi. Are the BSA Standard end blocks 24tpi? It would be nice (in an old fashioned way) if they are and the Standard cylinder id was also the same size as a cycle BB shell. Maybe I should take time out to rummage amidst the old cycle bits in the box in the shed.
Note that Raleigh old threads were 26tpi but they changed over to the accepted standard of 24tpi many many years ago.
Cheers, Phil