This is a top cap for a trumpet piston valve. It's from a rather old era, and new ones are no longer made, so it's for those who are looking for one. I believe it was originally attached to a Nikkan trumpet, but I don't know the exact compatible manufacturers. Please make your judgment based on the images provided. The threads are normal, so there are no functional issues. Inner diameter: approximately 2mm, outer diameter: approximately 2.1mm. I cleaned it thoroughly before listing, but there are some unavoidable small stains and scratches from use. There are no pets or smokers. However, individual perceptions may vary. It is, after all, a vintage item and a used item stored personally, so please check the images and refrain from purchasing if you are sensitive to details or concerned about minor imperfections (those in a hurry or those who make unreasonable requests). Also, although I inspect all items, it's a hobbyist's work, so there may be oversights. Please purchase only if you understand that it is a used item and that the current condition takes precedence.