Complete gear differential set for XRAY T3 includes composite differential case and cover with pulley. Differential gears are made from tough composite material, precision-molded composite gears combined with light aluminium hardcoated outdrives, which create a lighter and super-smooth gear differential. This differential is NOT factory pre-assembled. The advantage of the gear diff is that it is maintenance-free. When the diff is correctly built there is no need for maintenance for a very long time. There is no need to change oil on a regular basis, and there is no leakage due to the very good sealing system. The gear diff also increases on-power steering which is needed on almost all types of tracks.  Works great for both carpet and asphalt tracks. Fits both 50mm & 52mm drive shafts.