YAMAHA 48 Large Bore Trombone Mouthpiece Rim Inner Diameter: 25.25mm Throat Diameter: 6.62mm This mouthpiece has a very well-balanced rim and cup with a narrow backbore, and its high degree of completion allows it to meet the advanced demands of professional musicians. I received this mouthpiece from an acquaintance, but I am selling it because it doesn't suit me. It is a neutral and standard mouthpiece, for better or worse, and may be somewhat unsatisfying for those who use high-end mouthpieces such as Greg Black or Greg Willis. However, as you would expect from YAMAHA, a Japanese instrument manufacturer, the build quality is extremely high. It's a wonderful mouthpiece that allows you to return to your roots, in a sense, like a bowl of ramen at a casual neighborhood Chinese restaurant, where you think, "This is it."