Five-piece base set is made of high carbon steel. Reverse spiral flutes are designed to bite down to provide maximum gripping power. Universal lobular design fits all types of fasteners. 3/8 in square drive for use with hand ratchets, impact wrenches, air ratchets, hexagonal flats for use with flat wrench, pliers, adjustable wrench, sockets or VISE-GRIP locking pliers. Includes one each: 3/8 in , 7/16 in (11mm), 1/2 in , 9/16 in (14mm), and 5/8 in (16mm).