YAMAHA BB-68B Rim, Pink Gold Plating, GAT Extreme Treatment For sale as I no longer have the opportunity to use it. Please check the condition of the item in the photos. Rim Inner Diameter: 32.72, Throat Diameter: 7.50 Although the inner diameter of the rim is large, both the cup volume and throat diameter are small. On large tubas such as B♭ and C tubas, it gives clarity to the sound.