For various models:
BSA WM20, M20, M20WD, and M21 (1937 to 1947)
BSA M20, M21, B31, and B33 (1948 and up)
BSA A7, A10 with a plunger frame 'bolt on gearbox' & C11 4-speed
BSA A7, A10, B31, & B33 with a STD gearbox
BSA C10, C10L, C11, and C11G with a 3-speed gearbox
Partnumbers: 02-0433 / K139
