This is a trombone mouthpiece by JK (Yacht Club). It's an Elite Series Orchestra Model 5G, with an inner diameter of 25.5mm and a cup depth of MD. I had it gold-plated after buying the silver-plated version. I used it for about six months, so there are some scratches on the shank, but it shouldn't affect playing. I'm selling it because I switched to a different mouthpiece and no longer use this one. Please feel free to ask any questions in the comments section.