This is a Bob Reeves flugelhorn mouthpiece. The rim is a 41, and the underpart is 43N. It's compatible, and since the rim is smaller than the underpart, there's no noticeable step when playing. The combination of the 41 rim and 43N is excellent, and I think it's a setup that allows you to play from low to a wide range of notes. Retail price: 40,480 yen (tax included)