Fits with OEM flywheels. Sprocket shaft has keyway; use 23985-12 key (MCS 517945). Use nut (MCS 968011) on flywheel side. JIMS shafts are precision machined in Camarillo; California from a special order steel. Each and every part is thoroughly inspected and after heat treating all threads go through a special process to make them withstand greater torque stress. All shafts are ground to a 16 micron finish or better; unless specified otherwise. All ground diameters are concentric to well within .0003"; making truing and rebuilding quicker and with less effort.