The threading on BSA chainrings is almost certainly BSC or Whitworth and I guess the diameter is 1/4". The screws used are the same as on Williams chainsets through the 1950s and beyond, so there should be plenty about. Both BSA and Williams used small square-headed screws.
Hugh Thornton Cheshire, England
In a message dated 19/03/2007 22:16:47 GMT Standard Time, coelcanth@gmail.com writes:
does anyone know what threading was used on the BSA 5-pin chainrings that don't require fastening nuts ? i recently came across an old steel inch pitch ring with threaded bolt holes but i have not yet found a fastener that fits it..
thanks
Andrei Padlowski
Glen Ridge, NJ