The Yokomo Gear Differential Aluminum Drive Cup Set is a pair of optional aluminum joint cups for a gear differential that is standard equipment on the BD9 2019. It is a specification only for mounting a plastic protector on the universal shaft side. A hard anodized treatment has been applied to minimize wear. They are lighter than standard steel and effective for improving driving efficiency and acceleration response. By reducing the weight of the rotating part, the gyro effect is minimized, which is effective in improving exercise performance.