This is a rare, old-type GLANZ 2-piece trombone mouthpiece. It has a 7mm throat, a #4 backbore, and a #4 cup, and is no longer available. I purchased it for all-around orchestral playing. It has an inner cup diameter of 25.5mm, similar to a Bach 5G, but despite its depth, the high range plays well. It has a moderate resistance, and the #4 throat provides a good balance of air flow, covering the high to low range well. It can also be used for euphonium.