This is a copper tone ring for a trumpet bell. I purchased it new on Mercari, but it didn't fit, so I'm selling it. It was only used once, just for testing, so it's in near-new condition. The following is a quote from the purchase page: Made of hammered copper and forged, it has a beautiful hammered finish on the surface. It can be inserted and attached from the narrow part on the mouthpiece side of standard bells such as Bach and Yamaha. The lining is a single sheet of natural cork that does not contain adhesives. Material: Copper Inner diameter: 25mm Insertion opening: 20mm Unlike a Kranz, it is attached to the throat of the bell. It improves the resonance and monitoring. The sticky copper material provides a mellow and weighty sound. The use depends on your preference, but in my personal experience, it's useful for improving monitoring when playing pop music or combo jazz on a symphonic instrument. Also, during forte passages in an orchestra, the sound doesn't open up even at powerful ff, resulting in an energetic tone. It's an accessory that allows you to easily enjoy changes in sound.