RIBBED BRAKE DRUM B4-463 ! Fits  plunger frame Nortons and some of the racers.

BRAKE DRUM 16H NME2/463 ! Fits many prewar and postwar Nortons. British Made. Very nice quality. Studs 7/16 x 26TPI. Uses narrow 5/8 x 1/4” (520) chain. Was part number 9518, D2/468, E2-463