Brake drums are hollow cylindrical components utilized in drum brake systems, primarily on older vehicles or rear axles. They house the brake shoes and provide a surface against which the shoes create friction to decelerate the vehicle. Constructed from cast iron or composite materials, drums feature a machined inner surface to ensure consistent friction and heat dissipation. Internal ribbing and finning are common design elements to enhance cooling. Variations include self-energizing and duo-servo designs influencing braking force characteristics.