These formed steel plates take the torque of the rotor pushing the brake pads into the body of the Performance Friction ZR55 caliper. They protect the aluminum body from damage, but they do eventually wear. Notches, grooves, or indentations in these abutment pads will affect pad release. If the damage is deep enough, it could even affect braking. One size fits either front or rear calipers. Set of 8 repairs two calipers.