Aluminum engine mount plate and bolt set. These are washers used to secure the propeller with screws. We call them "one-yen coins." This is a custom-made product for attaching propellers, such as those on motor paraglider insurance, using a single screw instead of the usual 6 or 8 screws. I use these for all my engines. They make propeller installation very easy. Highly recommended for those who remove their propellers for transport. Only about 10 of these have been made in Japan. They are a valuable item. I still use this on my Top 80 and fly with it. It seems a radio-controlled spinner can be attached. - Material: Aluminum - Type: Mounting Plate with Bolt - Application: Used in Engine Assembly - Compatibility: Compatible with Specific Engine Models Thank you for viewing.