If you have ever installed a rocker stud into a cylinder head and watched it wobble as it screwed in - you knew that the rocker geometry was going to be inconsistent. ARP Rocker studs are concentric within .005 T.I.R thread pitch to thread pitch. They run straight and true. High-performance rocker studs are 170,000 psi tensile strength, while pro-series studs are 190,000 psi.