Drum brakes are a common type of braking system found on the rear wheels of many vehicles. While they serve the same purpose as disc brakes to slow the vehicle, they do so in a slightly different manner. Instead of using calipers to squeeze pads onto a rotor, brake drums use wheel cylinders to push brake shoes against the inside of a brake drum to slow the wheel. As they function using friction and contact, they eventually wear out over time and need to be replaced. Some important information for selecting the correct brake drum is the type of drum needed; braking system type (with or without ABS), shape and size, hole arrangement, fitting position and date limitation of the unit. As car manufacturers regularly update certain peripherals and design of their models, some brake drums will only be suitable for particular models of certain years.