All Pro Series bolts are cold-forged to ensure molecular integrity, heat-treated prior to thread rolling and machining, and aerated nominally at 200,000 psi. ARP Pro Series head bolt kits are application specific & designed for use with typically competition only components. These fasteners deliver superior strength and meet the ARP ZERO defect ZERO failure quality standard. Hardened and parallel-ground washers are included with each kit to ensure even load distribution and accurate torque readings. All Pro Series head bolts have a reduced wrenching hex or 12-point head and wide area flange to eliminate the need for valve train removal for cylinder head retorquing and permits the use of larger diameter valve springs. Most applications have undercut short bolts that can help eliminate head gasket failures through providing more stretch to compensate for the additional compression of gaskets.