For use with 23 or 18 deg heads that have perimeter bolt patterns with paralell spacing.RPM sheetmetal valve covers feature billet cnc 1/2″ thick 6061 aluminum rails, and hand formed 5052 aluminum bodies for an outstanding seal and appearance. Will clear any rocker arm combination. 1.75″ Billet Oil fill cap included. AN /NPT bungs available at an additional cost. ¬†See options