The 51D trombone mouthpiece has a large and deep cup. Designed for euphonium, this also works well for trombone players who desire a heavy, dark and rich tone. 25.24mm inner diameter, semi-deep cup Standard rim, semi-wide backbore Extra thick silver plating for added durability and longevity. Fits any brand or model of trombone, baritone or euphonium that uses a small shank receiver.