This is a bottom 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 compatibility with other manufacturers. Please refer to the images to make your own judgment. The threads are in good condition, so there are no functional issues. Inner diameter: approximately 1.8cm, outer diameter: approximately 2cm. I cleaned it thoroughly before listing, but there are some unavoidable small stains and scratches from use. I do not have any pets, and I do not smoke. However, individual perceptions may vary. It is a vintage item and is a used item that has been personally stored, so please check the images. Please refrain from purchasing if you are sensitive to details or concerned about minor imperfections (or if you are in a hurry or have unreasonable demands). Also, although I inspect all items, it is a hobby, so there may be oversights. Please purchase only if you understand that it is a used item and that the current condition takes precedence.