Oil seals are machine parts. It is a rubber seal for shafts and bearings. It is usually placed in the bearing cover. It has a circular shape with a shaft bore.
It is used, for example, in simple two-stroke engines to seal the crankcase space from the gearbox. This prevents unwanted leakage of fuel mixture from the crankcase to the gearbox as well as unwanted leakage of oil from the gearbox into the crankcase. Due to the friction between the seals and the rotating shaft, the seals wear out after a certain time and must be replaced with new ones.