The Gear Oil is responsible for protecting all your equipmentâs and vehicles vital parts like gears and bearings in drive axles and differentials, transmissions and industrial gearboxes. These oils come with a higher viscosity level, and with a purpose. It is to provide for easier distribution and protection of the entire gear set. The oil is a lubricant made specifically for transmissions, transfer cases, and differentials in automobiles, trucks, and other machinery. The Gear oil is used as a lubricant between the moving parts of a gear system so that the gears mesh and turn smoothly. It is available in various types.