Mainshaft bearing big
BSA WM20, M20, M20WD, and M21 (1937 to 1947)
BSA M20, M21, B31, and B33 (1948 up)
BSA A7, A10 in plunger frame (bolt-on) & C11 4-speed
BSA A7, A10, B31 & B33 with STD gearbox
Part number: 24-4065
This bearing is also used on Sunbeam 500cc S7/S8 as a crankshaft bearing.
