Edelbrock part #77791 Red Roller Rocker arms are designed for Big Block Chevy's using 7/16" studs. This 1.7:1 Ratio, single replacement rocker is manufactured in the USA from lightweight 7129 grade aluminum. The body is CNC machined then micro polished and anodized for durability. The trunnion race, roller pin and roller tip are centerless ground for superior quality. A high quality Torrington needle bearing fulcrum combined with a roller tip ensure smooth operation and performance. The full body design will accommodate up to 1.65" diameter springs. Thick-walled adjusting nuts and 4140 steel poly locks are included.