B - The "B" model is based off the Bach mouthpiece with a similar bowl shaped cup as well as the rim.

X - The "X" model is a high compression cup design. The X designation was designed for commercial players looking to add extra edge and projection to their sound.

XX - The "XX" model is a Medium depth cup with a reverse radius design. The XX designation was designed for players that needs more depth inside the cup, but still maintains a bright sound with excellent projection.

2 Piece Mouthpiece Backbores ONLY. You must already own an Xstream Top. Not compatible with other manufacturers tops.