ARP's Professional Series Head Bolt Kits 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. Professional Series head bolt kits are application specific and designed to deliver superior strength typically associated with competition engines. These kits are available in standard 8740 - 190,000 psi tensile strength material or proprietary ARP2000 - 220,000 psi tensile strength material. All Pro Series head bolts have a reduced wrenching hex or 12-point head and wide area flange to permit the use of larger diameter valve springs and eliminate the need for valve train removal during cylinder head retorquing.