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.