Supports the transmission main/shaft when the inner primary was discarded for an open belt. Our transmission main/shaft bearing support is cast from 356 T6 high strength aluminum with an automotive style sealed ball bearing to fully support the main/shaft with all the weight of the clutch basket and associated parts. Fits 1965-up Big Twin 4-Speeds w/rear chain only. Will not work with super nut. Must use stock main/shaft nut.