The Super Twin 2 Piston caliper was developed as a "Quick Change" direct replacement for GM's Full size single piston calipers. These calipers were commonly used on the early GM A, F & X bodies and the 71 & up B-Body cars. This 2 piston caliper has a forged aluminum housing with 2-38mm or 2-43mm stainless steel pistons. Using the stock style brake pads the 2 pistons of the Super Twin caliper provide more clamping force and spread the load across the entire brake pad. This added clamping force and load distribution of this caliper will give you the braking power your car needs!