TMS Kobo Original Sound Improvement Goods Rotary Spacer-kun (Copper Hammering & Heat Treatment) These sound improvement goods are inserted between the rotary caps of a French horn. They change the ease of sound production and resonance. They offer the rich resonance of copper and the good sound initiation due to hammering. Furthermore, heat treatment enhances the sound. Can be used for Alexander 1-3 horns. I think it can also be used for other horns. Outer diameter 22, thickness 1.5, hole diameter 10.5 Made of copper