What kind gear oil put in 50cc?

For a 50cc two-stroke engine, it's typically recommended to use a high-quality two-stroke oil mixed with gasoline, rather than gear oil. However, if you're referring to a gear system, such as in a scooter or small motorcycle, a lightweight gear oil, like 80W-90 or a specific gear oil recommended by the manufacturer, is usually appropriate. Always consult the owner's manual for the specific type and viscosity recommended for your particular model.