Front Left Black Ops Differential Bore 4-Piston Caliper (0053-2919-SMB) by Performance Machine®. This high performance caliper features an ultra clean look and Performance Machine proven differential bore technology for optimal brake performance. Style and function merge for an ultra-clean look with proven technology for optimal braking performance. Each caliper is machined from billet aluminum to eliminate flex. Subjected to rigorous testing on the PM brake dyno to ensure performance.