Lucas Synthetic 50 wt. Trans Oil is designed especially for heavy duty truck transmissions but can be used in many other applications. Common gear oils are mostly base stocks with little more than an addition of sulphur and phosphorus as a total anti-wear package. We at Lucas Oil consider this inadequate. Most heavy duty truck transmission manufacturers now consider sulphur and phosphorus to be potentially corrosive to copper and brass and consequently recommend against common gear oils for this reason. The other 50 wt. gear oils we have tested, synthetic or otherwise, are pure base stock, we consider this also inadequate. Lucas Synthetic 50 wt. contains an exclusive additive concentrate derived from synthetic oil that ensures lower operating temperatures and better lubrication, especially to upper bearings and gears. This is a long lasting fluid that is far superior to conventional synthetic fluids and contains nothing that could be harmful.