Front/Rear Active Differential set for XB4. The unique XRAY Active Differential is a superior, adjustable front side gear differential for XB4 ... vastly improving the buggy's speed and handling faculties. The unique design regarding the interior elements making use of various angled sections permits the diff gears to activate on-power to boost the forward traction, which makes it quicker and simpler to drive. As the XRAY Active Differential is a performance selection for serious racers who want to gain an advantage on superior speed and control, additionally it is of good advantage to motorists of amounts that want an even more predictable and easy-to-drive car in every race conditions. Ball-bearings not included Fits XB4'20-21