With the exception of the "junior" mouthpieces, Nos. 30E and 32E, Bach tuba mouthpieces can be used equally well on BB-flat and E-flat tuba. There is no good reason for making mouthpieces for E-flat tuba any smaller or shallower, because a player using an E tuba actually transposes a fourth and uses the instrument in the lower register, for which a larger-sized mouthpiece is to be given preference. Nos. 7, 18, 24W and 24AW have larger backbores.Standard Tuba/Sousaphone mouthpieces.