aobi Front&Rear Pair Avid BB7 Disc Brake Calipers Cycling DIY Kit 0MM IS is front Brake, and 20MM IS is Rear Brake Easy-to-use adjustability thanks to Dual Knob Pad adjustment, Tri-Align Caliper Positioning System With Tri-Align Caliper Positioning System, Simply loosen CPS bolts slightly, then squeeze brake lever while re-tightening bolts, and continue your ride Mountain bike rotor brake offers fine-tuned, modulated braking power Conversion base 0mm is or 160F 140R (front wheel disc brakes with 160mm discs), Conversion Block 20mm is or 160R (rear disc brakes with 160mm discs)