This is a K&G bass trombone mouthpiece. It's a size 0.5 with an inner diameter of 28mm. There are two cup depths, D and E, and this is the deeper E cup. I liked the crisp, responsive sound, but I'm selling it because I've changed sizes and don't use it much anymore. There are some shank insertion marks, but no dents. I plan to ship via Yamato Compact.