Oil seal is the usual name of general seal, which is simply the seal of lubricating oil. It is used to seal grease (oil is the most common liquid substance in the transmission system, also generally refers to the general meaning of liquid substance). It separates the transmission parts that need lubrication from the output parts, so as to prevent the leakage of lubricating oil. Static seal and dynamic seal (general reciprocating motion) seal called oil seal.