Used to lock the pinion gear in place, allowing the mechanic to install the (left hand threaded) pinion gear nut with correct torque. Includes tapped holes to store mounting screws for both 1954-69 (1/4-24 thread) and 1970-99 (1/4-20 thread) screws. Cerakote coated. Note: To install/remove the pinion gear nut see 998370 Fast Eddy pinion gear nut socket.