This is a silver-plated Vincent Bach trombone mouthpiece. For large bore trombones. It has the same rim shape and diameter as the No. 4 for small bore trombones. Versatile and good for playing both high and low registers when playing solo. ■ Diameter: 26mm ■ Cup Depth: D (Deep) ■ Rim Thickness: MW (Medium Wide), slightly rounded rim. I used it for a test play, but only once or twice, and then I cleaned and stored it. There is almost no sign of use. It will be sent in the original box.