Fits 1989 to 2002 12 & 24 Valve 5.9L Cummins engine block. Billet rear freeze plug features 1/2 npt threaded center hole with plug (can be removed to accommodate coolant bypass). Design includes o-ring seal and mounting bolts. Helps prevent blow out at high rpm’s, a weakness of stock freeze plugs. Also available without 1/2 npt bypass port.