Ultra ARC Aluminum Series Rocker Arm for Ford FE Big Block 3/8-24 Adjusting Nut. The Comp Cams Ultra ARC Aluminum Series Rocker Arms increase engine power, improve valvetrain stability, and enhance oiling efficiency. Their extruded design—developed using FEA analysis—creates a stronger, stiffer rocker body without adding unnecessary weight. The ARC series rocker arms feature an Arced, Recessed, Contoured design delivers an optimal strength-to-weight ratio. Backed by a Lifetime Warranty—buy them once and use them forever. Engineered for applications running up to 700 lbs of open spring pressure.