This is a mouthpiece created in collaboration with XO Trombone Project and Masahito Nakagomi of "Willie's Custom Brass." Based on the old Bach mouthpiece size, it is very easy to play, even for beginners, and the design is ideal. [Specifications/Features] Inner Rim Diameter: 25.50mm Features: Wider and rounder rim than 6 1/2AL, with a slightly deeper cup for a powerful sound.