If you're using a mechanical speedo cable, you'll need to cover the port with a plug. This plug will block off the mechanical speedometer port opening on Tremec TKX, TKO, 3550, Borg Warner T-45, Ford T-5 and the T-56 Magnum transmissions. If you're running an electronic speedometer this is a must have. This high quality plug is machined out of billet aluminum. The o-ring is also included to prevent fluid leaks. Does not include bolt.