Limited Edition TMS Kobo Original Sound Improvement Goods Rotary Spacer-kun (Brass Hammering Model) ① This is a sound improvement gadget to be inserted between the rotary caps of a horn. It changes the sound's responsiveness and resonance. It has a good start-up due to the brass hammering. Can be used for Yamaha, Alexander, and Holton. I think it can also be used for tuba and trombone. Outer diameter 21.5, thickness 1.5, hole diameter 10.5