- Ian Bousfield C4 mouthpiece for tenor and bass trombone; Classic Series; wide shank; inner diameter: 1.024" (26mm); outer diameter: 1.550" (39.37mm); bore: .255" (6.48mm); silver plated; developed with international trombone soloist Ian Bousfield; manufactured with high level CNC technology THIS ITEM IS CURRENTLY NOT AVAILABLE YOU CAN CONFIRM THIS INFORMATION BY CLICKING ON ITEM