Drum brakes are actuated by brake shoes pressing against the brake drum to generate braking force, and they come in two types: internally expanding and externally restrained. Internally expanding drum brakes use the inner cylindrical surface of the brake drum as the working surface and are widely used in modern vehicles; externally restrained drum brakes, on the other hand, utilize the outer cylindrical surface of the brake drum and are currently only used as parking brakes for a very limited number of vehicles.