Yamaha Signature & Replica Series, Doug Yeo Inner Diam. (mm) Rim Contour/ Thickness Cup Depth Throat (mm) Backbore Playing Characteristics 28.72 semi-flat/ semi-thin semi-deep 8.0 semi-wide Large-sized bass trombone mouthpiece with a wide dynamic range-from thundering fortissimo to the most delicate pianissimo. The well balanced response and big rich sound are especially well suited for a large orchestra. Gold-plated rim, cup, and inner bore.