Model Number: 31D Silver Plated Inner Gold Inner Diameter: 17.3mm Throat Diameter: 4.3mm Cup Shape: U Cup Shank: American Purchased about 3 and a half years ago for 26,400 yen, and then gold plating was applied to the inner gold. The rim is thin, and the cup is medium. It gave the impression of producing a soft and smooth sound. It had good response, and was an easy-to-play mouthpiece, making lip slurs and the like easy. I am selling it now as I am no longer using it. There are scratches on the shank from when it was attached to an instrument. It will be shipped in the original box.