GRIEGO Mouthpiece BB1BT Brian Bowman Model Large Shank 【 Item Details 】 While the specifics aren't public, the inner rim diameter is said to be between the GRIEGO mouthpiece sizes 6.5 and 7. ■BB1: This model features a deep cup and a large backbore, allowing for a wide range of expression in both high and low registers, with a core sound and extended sustain. The inner rim diameter is not very large. - Brand: GRIEGO - Type: Mouthpiece - Model: BB1BT - Accessories: Original Box GRIEGO Trombone Thank you for viewing.