Precision machined from a low alloy nickel; chromium; molybdenum case hardened steel. Offers .0005″ parallel tolerance on the flats of the shafts. Perfect for performance applications with increased spring pressure. Upgraded replacement for 17300053 (front exh; rear int); 17300055 (front int; rear exh) and 17300059B (set). Note: See 585911 for identical rocker arm shaft kit; complete with mounting hardware.