All Pro Series bolts are cold-forged to ensure molecular integrity, heat-treated prior to thread rolling and machining, and meet the ARP ZERO defect - ZERO failure quality standard. ARP Pro Series head bolt kits are aplication specific and designed to deliver superior strength typically associated with competition engines. Pro Series kits are available in standard (8740) 190000 psi tensile strength material and proprietary (ARP2000) 220000 psi tensile strength material where noted. All Pro Series head bolts have a reduced wrenching hex or 12-point head and wide area flange to premit the use of larger diameter valve springs and eliminate the need for valve train removal during cylinder head retorquing. Hardened parallel-ground washers are included in each kit. 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.