Socket is designed to fit in the cyliner head on m42 and m50 engines to remove and install cylinder head bolts spring loaded detent ball holds bolt in place works with 1/2″ ratchet, breaker bar, or torque wrench socket size is e12 for external torx bolts socket is designed to fit in the cylinder head on m42 and m50 engines to remove and install cylinder head bolts.spring loaded detent ball holds bolt in place.works with 1/2 in. ratchet, breaker bar, or torque wrench.socket size is e12 for external torx bolts.