This can prevent the slip of the propeller, spinner, cooling fan etc.
When the engine generates knocking, it is hard to loosen the nut and you can safely use it.
Especially it is a necessity for 4 cycle engine.

Specifications

• Hole diameter: 8.0mm
• Out diameter: 25mm
• Compatible engine (2C): 50-91
• Cmpatible engine (4C): 70-91