Chain drives use a chain connected between a sprocket at the transmission output and a sprocket attached to the rear wheel. Drive chains consist of a number of links that contain pins, rollers, bushings, and plates. O-rings work in conjunction with the pins, plate, and bushings to hold lubrication inside the pins and rollers. Rollers and pins have the same axis of rotation -- pins are enclosed in the rollers. Rollers make contact with the sprockets and need to rotate freely in order for the power from the engine to be transferred cleanly.