KELLY tu25cg 25 Glow in the Dark Plastic Tuba Mouthpiece KELLY Tuba Mouthpieces are made entirely of Lexan material. The 18, 24AW and 25 cup sizes are patterned after the Bach series, while the KELLYberg is patterned after the Conn-Helleberg series. All cup sizes are sampled by our professional staff and are adjusted to produce our final, comfortable, easy-blowing mouthpieces. All of our mouthpieces are identical to exacting standards. FEEL the Comfort!