All Pro Series bolts are cold-forged to ensure molecular integrity, heat treated prior to thread rolling and machining, are are rated nominally at 200,000 psi. ARP Pro Series head bolt kits are application specific. 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 and a wide area flange. For 1997-2003 LS engines and some 2004 LS engines using “unequal length” bolts.