ARP Hex Head Bolt Kit LS6/LS2 Heads, 2004 and up. These Pro series cylinder head bolts from ARP are cold-forged to ensure molecular integrity. They are heat-treated prior to thread rolling and machining, and are rated at a whopping 190,000 psi. The Pro series are also available with hex and 12-point heads. All kits come complete with hardened parallel washers for even load distribution and accurate torque readings. Picture is for reference only.