Bach produces many different models so that each player can find the best mouthpiece for their individual embouchure. Depth of cup: Medium deep Approx Cup Dia: 25.40mm Rim Shape: Medium wide, well-rounded. Throat: .276" "G" Backbore: 420 Description: The same cup, throat, and backbore as No. 2AL small shank tenor trombone but with bass shank. It requires a well developed embouchure. At Alamo Music Center we take pride in knowing we carry the best accessories for all your Band & Orchestra needs. Please feel free and call us with any question regarding this mouthpiece at (210)224-1010