YOKOMO Aluminum Ball Diff Kit for YD-2 Series (Y2-500AA) A set of ball differentials that can be used on all YD-2 series cars. The left and right differential housings are made of aluminum, resulting in a light weight finish. While taking advantage of the height of the traction unique to ball differentials, there are many advantages such as improved throttle response due to its light weight and increased exercise performance by reducing the gyro effect. In order to minimize the wear of aluminum parts, a plastic protector is attached to the end of the universal shaft dogbone, and the clearance is optimized to further increase the response.