Upgraded replacement for the OEM rocker shafts. With a 66% strength increase when compared to the OEM shafts for better reliability, especially in high lift/stress applications like exist with high-lift cams. Bearing quality steel and precision centerless ground. OEM replacement reference 17300053 (front exh, rear int), 17300055 (front int, rear exh) and 17300059B (set). Note: S&S advices to install these rocker arm shafts in combination with MCS 588917 rocker arm tower stud & nut kit.