This is a practice mute for French horn. I bought it out of necessity and used it for about a month. After that, I no longer needed it, and it has been gathering dust in my closet, so I'm offering it to someone who can use it. As shown in the second photo, the mute can be split into top and bottom halves, and the attachments inside seem to allow you to adjust the volume and resistance. I used it with an Alexander 103. I don't know about fitting it to other instruments (the website doesn't seem to mention it). Since I don't have the box, I will wrap it in bubble wrap for shipping. From the website: Features of okura + mute ● Suppresses unwanted vibrations and cuts out uneven sound. ● The body can be opened and closed to keep the inside clean. ● You can choose from two sizes of air holes. Practice is possible by utilizing the difference in resistance. Practice mutes tend to focus on soundproofing performance and good playing feel. However, the most important thing is the comfort of the sound you hear. In 2013, the handmade practice mute <okura+mute> was born, which does not compromise playing technique and has the potential to help you improve. It quickly spread to players around the world, and inquiries from all over the world continue to pour in. From the desire to have more players experience it, the new okura+mute has been completed. okura+mute has a comfortable feel that provides good soundproofing and makes you want to keep playing. - Toshio Okuda, the inventor, trumpet player