Five-piece expansion 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 5/16 in (8 mm), 10 mm, 13 mm, 11/16 in and 3/4 in (19 mm) bolt grips.