An integral part of the braking system, the handbrake drum is a metal cylinder which bolts onto the wheel. When the handbrake lever is pulled up, brake shoes which sit inside the drum work provide resistance to the drum and stop it from turning.
Like any metal part, handbrake drums for every make and model of car are subject to corrosion, rust and the wear and tear caused by frequent usage. When this reaches a certain level the handbrake drums must be replaced to maintain handbrake integrity.