Friction clutch plate for 6-spring clutch.
Made by Surflex
BSA C10, C11 (1946-53)
BSA B31, B32 (1946-57)
BSA M33, B33, M20, B34 (1948-57)
BSA A7, A10 swing arm models (1954-57)
BSA M21 (1948-63)
Part numbers: 653857, 653825, 423119, 18-M-13, 65-3857, 65-3825, 42-3119
See photo 2 for dimensions.