Well-balanced rim and cup with a fairly narrow backbore. Model : 48 Rim Inner Diameter : 25.25 Rim Contour : standard Rim Thickness : standard Cup Depth : standard Throat : 6.62 Backbore : semi-narrow Trombone Mouthpieces - Standard Series Quality brass mouthpieces contribute to the high regard Yamaha has earned among beginning and professional musicians alike. The result of a special approach to design and manufacture, Yamaha mouthpieces deliver the performance and comfort required where they are needed most: where instrument meets musician. The mouthpiece production technique used by Yamaha promises consistent quality mouthpieces, time after time. Other manufacturers use a specific cutting tool to create every mouthpiece, which causes problems as tools start to wear. This can result in inconsistent quality and poor performance. Our computer-aided design system and computer controlled lathe work together to produce the most precise, consistent mouthpieces in the world.