BSA C11/C11G/C12 Piston +60 Assembly complete with Gudgeon Pin, Piston Rings and Circlips
250cc
Piston Clearance 0.12mm or 45thou
C11 1939-55
C12 1955-58
can also be used for C10, even if they usually had a flat top
measurements see last pict. and techn. data