Bach Large Shank Trombone Mouthpiece Silver 5G Size 5G Cup Depth is Deep Rim Shape Med Wide Semi Flat Model No. / Depth of Cup / Approx. Cup Dia. / Rim Shape / Throat / Backbore / Description 1G / Deep / 28.00 mm / Medium thin, well rounded. 1-1/4G / Deep / 27.50 mm / Medium thin, well rounded. / .276" / 429 Cup diameter is smaller than No.1G, but still very large and deep, with the sonority preferred by the modern American school. 1-1/4