This Impact Rated(TM) socket-head screwdriver bit by Craftsman(R) is made of black-coloured steel. Featuring a magnetic tip, it lets you fasten 5/16" nuts and bolts with ease. With a length of 4", it is strong enough to withstand the high torque output of an impact driver, but can also be used with a regular drill. The recessed corners drive fasteners on the flats. helping to minimize the buildup of metal shavings and reduce rounding of the hexagonal head.