Yamaha GP Mouthpiece Trombone 51L, Mouthpiece for Trombone, GP series, Golden rim and bore, Big shank: 51-GP, Inner diameter: 25.23 mm, Standard contour, Standard thickness, Standard cup depth, Bore: 6.92 mm, Fairly narrow backbore, Well-balanced rim and cup with a fairly narrow backbore., Elaborated design, which particularly meets the demands of professionals