These O-Rings are the exact replacements for the ones that are included with the Scorpion 22mm airplane motors, and the Scorpion 3mm Prop Saver Adapters. You get 10 O-rings in this package, so you always have a spare at the flying field. To insure a safe, secure hold of the prop on your Prop Saver, always inspect the O-ring after every prop change. If the O-ring is nicked or cut, make sure to replace it.