Skeleton oil seals are the typical example of oil seals. Generally oil seals means skeleton oil seals. The function of oil seals is for insulating the part which need lubrication in transmission parts and outside environment. The lubrication oil can not be permeated. Skeleton just like the steel bar in concrete for gain in strength and keep the shape and tension of oil seals. Oil seals have single lip oil seals and double lip oil seals. The second lip of double lip oil seals can prevent dust, then the dust and impurity can not go inside of machine. Skeleton oil seals also can be divided according to package seal, and seal the exposed skeleton oil seal assembly. According to the working conditions, it can be divided into rotary skeleton oil seal and round-trip skeleton oil seal. Used for crankshaft of gasoline engine, diesel engine, gearbox, differential, shock absorber, engine, axle, etc.