Competition Cams 1431-16 Magnum Roller 1.6 ratio, 3/8" Stud Diameter Rocker Arm for Small Block Ford (Rail Type) Ultimate street rocker designed for serious performance enthusiasts Constructed from 8620 chromemoly steel, a superior material that will not flex and assures maximum lift Roller tip reduces friction while stiff design and superior ratio accuracy yields more effective valve lift 15 to 30 horsepower increase over stock rocker arms Use in any applications with less than 350 lbs. open spring pressure