The prop saver consists of a hub that mounts on the prop shaft. The hub has two pins (or bolt heads) that stick out perpendicular to the prop shaft. The prop fits against the front of the hub and is held in place by a small rubber band that is stretched from one pin, across the prop and onto the other pin. If the prop hits something, the rubber band comes off and the prop is released. Some people swear by prop savers, but I've seen props fly off for no good reason. One time a fellow at my field was taking off and just as the plane cleared the ground the prop came flying off, missing me by inches. Since props are so cheap, I would never use a prop saver.