This handly little device mounts directly to the shaft of your electric motor, and in the event that the prop touches the ground during landing, allows your prop to "pop off" the motor instead of breaking the prop.  The prop is held onto the Prop Saver with a small rubber "O-ring", which is included.  This one is designed for a motor with a 3.17mm shaft, and fits the CF2822-14 motors we use on our Night Flyers.  Great for foamies that don't have a landing gear, it keeps you from breaking your prop even when you make a good landing!  
 
Price is per pair (set screws and O rings included).
 
Note: We have replacement O-rings for available, but they are a common plumbing part, available at most any hardware store.