A crankshaft drive side oil seal to fit many BSA and Triumph unit singles. This is a special thinner version of the original part numbers 40-0025, which is required when you have the special 18T engine sprocket for trials gearing.

Triumph TR25W 250/441cc (1967-72)
BSA C15/B40 Distributor 250/350cc (1959-64)
BSA C15/B40 Sports Star 250/350cc (1964-)
BSA C25/B25 250cc (1967-)
BSA B25/B44 250/441cc (1967-72)