Actually there was more similarity in thread pitches between BSW and UNC, w hereas I think none of the UNF and BSF pitches matched. Even when the pitch was the same they wouldn't necessarily fit together, because BSW and BSF ( also BSP, BSB, ME) used a 55 degree angle, while Unified threads used 60 de grees, just the same as metric. American pipe threads use 60 degrees as wel l, which can be a pain when tring to connect up US made equipment. Just to be different, BA threads are 47.5 degrees...