A caliper disc brake functions like an ordinary rod cylinder. Components consist of a piston, a puck ( or pad ) or wearable friction material, a housing, and opposing side and a disc on which the brake acts. When pressure is applied to the piston, the puck is moved into contact with the disc, causing the disc to stop rotating or, in a tensioning application, to supply constant drag. The housing contains the piston and puck and is located above the disc. There are always two sides to a caliper disc brake: One is known as the live side with the piston and puck; the other may be either another live side or it may be a dead side (another puck which contacts the disc when the live side piston is actuated).
Disc brakes are widely used in three areas: Stopping, retarding (tensioning), and holding. In any application it is necessary to determine how much torque is required, how much heat will be generated (and thus, to be dissipated) and the anticipated service life of the linings. Once these variables are determined, then find the combination of disc and caliper that will most economically meet these requirements.