An oil seal is a customary term for a general seal, simply a seal of a lubricant. It is a mechanical component used to seal grease (oil is the most common liquid substance in the transmission system, also refers to the general liquid substance), it isolates the parts of the transmission parts that need to be lubricated from the output parts, so as not to let lubrication Oil leaks. Static seals and dynamic seals (generally reciprocating) are called oil seals with seals.