Model Number: 2DM - A1 Silver Plated Inner Diameter: 17.50mm Throat Diameter: 4.2mm Cup Shape: U Cup * Although JK appears to have its own unique shank, it worked without issue on American shank instruments. Purchased one week ago. Used a few times, and the cup appears to be clean both inside and out. There are scratches on the shank from attaching to the instrument. Will ship in the original box.