This is a JK French horn mouthpiece. Model: 1DM Outer rim diameter: 26.0mm Inner cup diameter: 18.0mm Throat: 4.2 Cup shape: U-cup Silver-plated finish Highly recommended for those who want to play with a big sound and powerful low notes. While an inner diameter of 17.5 is common, Japanese people tend to have larger front teeth, and using an inner diameter of 18.0 may solve some problems. Please try it if you are having trouble. New reference price: 13,000 yen (tax included)