COMP Cams Top Dead Center Stops are designed to positively stop the piston in order to find top dead center. The bolt style screws into the spark plug hole, while our universal plate type bolts across any cylinder bore when the heads are off. PartNumber : cca4795 Description : Top Dead Center Stops; 18mm Bolt-Style; Heads On (Big Block Ford) Title : 4795 Bolt, 14MMX1.25 Piston stop California Proposition 65 : WARNING: Cancer and Reproductive Harm P65Warnings.ca.gov Engine Components::Engine Uncategorized