Re:
From memory, the older Williams, and 5 pin types from about 1900 on, had square headed screws which were 3/16 inch by 32 TPI, the old 2BA is just slightly slack. The Williams sleeve fittings used the same thread, I am not aware of them being common to anything else.
The same 3/16 thread was used on British fork end mudguard eyes, not Raleigh.
Keith