Oil seal, 9/16" x 1" x 3/16", contact breaker on BSA A50, A65, A75, Triumph T20, 3TA, 5TA, T90, T100, T120, TR6, TR5T, T140, T150, T160, kickstart shaft on BSA B25, B40, C15, C25, timing side crankshaft on Triumph T100, T120, T140