This is the Greg Black trombone/euphonium mouthpiece 5GSD L [Light]. It's a versatile model with a cup depth between a 5GS and a 5G. Due to its light weight, it should fit well with any instrument and be easy to handle. (Greg Black's light weight is similar to a standard weight of other brands.) I purchased it, but it didn't produce the sound I was looking for, so I'm offering it to someone who wants it.