COMP Cams 1802-16 Ultra Pro Magnum 3/8" Stud Diameter XD Roller Rocker Arm for Small Block Chevrolet For Small Block Chevrolet applications 1.6 inches ratio; 3/8 inches stud Machined billet pushrod seat insert 8650 steel construction outlasts and outperforms other rockers in accuracy and strength Ultra Pro Magnum XD rocker arm bodies are guaranteed against breakage for life