Performance Machine Four-Piston Differential-Bore Front Calipers For Harley High performance pads and stainless lines are only half measures. If you want to really upgrade the stopping power on your Harley replace your front caliper with a 4 Piston Differential Bore Caliper from Performance Machine. Trust the leading name in V-Twin brakes to handle the stopping duties on your machine. Features: Caliper is 4 piston differential bore with dual pad design Differential bore pistons apply different forces at the leading and trailing edge of the pad to ensure long life Designed for 11.5 and 11.8 disc applications Requires 11/16 master cylinder 501-058, or 501-057 or 501-059 for optimal performance