BSA USED A BASTARD SIZED VALVE STEM ON VARIOUS GOLD STARS BOTH INLET AND EXHAUST AND USED ON BOTH 350 AND 500 MACHINES IT WAS .348". THESE VALVES WERE GROUND SLIGHTLY SMALLER AT THE TOP OF THE STEM WHERE THE COLLETS FITTED,REDUCED TO .342". I HAVE 3 DIFERENT VARIATIONS OF THIS COLLET.#1 #2 #3

FOR DIMENSIONS USE SECOND PICTURE CHART:-

A    .439"

B    .585"

C    .342"

D    .447"