This is a large F/Eb tuba mouthpiece, and the smallest CC/BBb tuba mouthpiece available. This mouthpiece is ideal for full size tubas in small to medium Bands, and orchestras. Based on a Helleberg 7b, but with better pitch, articulation, and clarity of sound. Great for large F/Eb tuba excerpts in an orchestra, or band. Rim is 1.255 and the throat is .318″ diameter, deep funnel shape cup.