This is a 100ml bottle of Ultimate Racing 4,000 cSt Silicone Differential Oil for 1/8th scale off road buggies (and some 1/10th scale on-road touring cars). Ultimate Racing differential oil is made from 100% pure silicone oil and will not thin out in hot weather or thicken up in cold weather. The thicker the oil, the less your differential will "diff out" in the corners, where the two tires will turn at different speeds. Changing the differential oil in your diffs is one of the most important tuning options for off-road buggies. Ultimate Racing silicone oil content antifriction additives to minimize viscosity changes.