Clutch Masters 2-Piece Billet Aluminum Flywheels are made from the highest quality 6061-T6 or better grade aluminum. This material is chosen for its properties that are much more suitable for the environment than the one-piece chromoly units, with regards to heat dissipation and serviceability. The replaceable friction surface used is incredibly tough high carbon steel. This allows mating with any type of clutch friction material without worry. The starter ring gears are made of high carbon heat-treated steel for long lasting durability. The unit is buttoned together with military grade fasteners to make the premier flywheel in the industry.