Yamaha Trumpet Mouthpiece 11B4 Inner Gold. Due to the inner gold plating, the backbore also has gold plating. Used only a few times. TR-11B4 Cup Volume: B Rim Inner Diameter: 16.46mm Throat Diameter: 3.65mm With a slightly shallow cup and a medium rim, it is rich in durability and ideal for wind orchestras. With a brilliant tone, it is also suitable for D, E♭, and piccolo trumpets. (Reference: YAMAHA JAPAN) The rim inner diameter size is about halfway between Bach 7 and 10-1/2C. It has a semi-flat rim with normal thickness. It has a soft rim design for comfortable lip contact. The rim outer diameter size feels about halfway between Bach 7 and 10-1/2C. The inner edge of the rim is slightly defined. The cup is slightly shallower than Bach C, about the same as Bach D. The throat is 3.65mm. The backbore is about Warburton 9. It produces a core sound with a thick, dense tone that carries well. Because of its orthodox sound, it is a mouthpiece that can be used for all genres. (Reference: Net Brass)