If you have ever installed a rocker arm stud into a cylinder head and watched it wobble as you screwed it in,- you knew from the beginning that the rocker arm geometry was going to be inconsistent and all over the place. ARP rocker arm studs are concentric within .005 T.I.R. thread pitch to thread pitch. They run in straight and true. lengths are exact- designed to provide positive seating every time. An extra-large radius base offers greater resistance to flex. Available in both high performance and pro series. Designed to be used with ARP's Patented Perma-Loc Adjusters. High Performance Series studs are made from 8740 chrome-moly steel and heat treated to 180,000 psi. Excellent for E.T. bracket racing, limited rule oval track competition and street use. Tip ground flush for optimum adjuster seating. Pro Series- Designed for competition applications ARP's pro series rocker arm studs are made from premium grade 8740 chrome-moly steel and are heat treated to 200,000 p.s.i.