Hub Brakes or drum brakes operate like those of a car, although the bicycle variety use mechanical rather than hydraulic actuation. Two pads are pressed outward against the braking surface on the inside of the hub shell. Shell inside diameters on a bicycle drum brake are typically 70 – 120 mm. Drum brakes have been used on front hubs and hubs with both internal and external freewheels. Both cable- and rod-operated drum brake systems have been widely produced. A Roller Brake is a modular cable-operated drum brake manufactured by Shimano for use on specially splined front and rear hubs. Unlike a traditional drum brake, the Roller Brake can be easily removed from the hub. Some models contain a torque-limiting device called a power modulator designed to make it difficult to skid the wheel. In practice this can reduce its effectiveness on bicycles with adult-sized wheels.