Designed Specifically For Drag Racing, Pro Series 4 Piston Directional Calipers are aluminum directional calipers with stainless steel Pistons. Aluminum bodies drastically reduce weight, pistons are 1.625? & 1.750? to vary pressure on the pads decreasing pad taper. Stainless steel pistons are corrosion resistant and anti-rattle clips reduce brake pad vibration and noise.