HIGH PERFORMANCE SERIESHigh Performance head bolts are available with a reduced wrenching hex or 12-point and wide area flanged head that eliminates theneed for valve train removal to facilitate cylinder head retorquing. All High Performance Series bolts are 180,000 psi (which is 15%stronger than Grade 8) and kits come complete with hardened parallel-ground washers.PROFESSIONAL SERIESAll Pro Series bolts are cold-forged to ensure molecular integrity, heat-treated prior to thread rolling and machining, and meet theARP “ZERO defect – ZERO failure” quality standard. ARP Pro Series head bolt kits are application specific and designed to deliversuperior strength typically associated with competition engines. Pro Series kits are available in standard (8740) 190,000 psi tensilestrength material and proprietary (ARP2000®) 220,000 psi tensile strength material where noted. All Pro Series head bolts have areduced wrenching hex or 12-point head and wide area flange to permit the use of larger diameter valve springs and eliminate theneed for valve train removal during cylinder head retorquing. Hardened parallel-ground washers are included in each kit. Most applicationshave undercut short bolts that can help eliminate head gasket failures through providing more “stretch” to compensate for theadditional compression of gaskets.