Aussiespeed CNC machined billet alloy rocker cover spacers. These are any easy alternative when installing roller rockers. They allow an additional clearance for rockers, posi locks and stud girdles.will fit SBC engines from 283 to 400 cast iron & aluminum performance cylinder heads.These risers are a solution for retaining factory look corvette,Chevy painted tin valve covers for that std looking engine bay & get the performance gain of roller rockers & updated valve train components.