Performance MacHine Diff Bore 4-Piston Front Caliper Right Chrome H-D All 00-11Harley Davidson Brake Caliper Performance Machine 11. 5" 4 Piston Caliper is a 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 1 2"; disc applications Requires 11 16"; master cylinder 501 058, or 501 057 or 501 059 for optimal performance Features differential bore pistons that apply a different force at both the leading