ARP Main Bolts, Superior to any other main bolt and designed to exacting standards and demands of professional engine builders. ARP Main Bolts are forged from 8740 chrome moly steel. They feature reduced wrenching head and large underhead radius. The threads are rolled after heating treating giving them about 2000% better fatigue strength than bolts that are heat treated prior to threading. High Performance Bolts are rated at 180,000 psi. The Pro Series are application specific designed for competition engines and rated at 190,000 psi. Hardened parallel-ground washers are included with each kit.