Product Description Specifications This Ultra Pro Magnum rocker is made of black oxide coated 8650 chromemoly steel that can withstand up to 850 lbs of spring pressure. Featuring a 1.6 ratio, this rocker fits Ford 289-351W with a 3/8" diameter stud. Category: Engine Components>Rocker Arms Core: N LTL: N MPN: 1631-1 Proposition 65: Y Special Order: Y