The Stonelined Bass Trombone Straight Mutes feature outstanding precise and crisp sound within the entire register of the instrument with excellent intonation. The model 198 is designed to fit larger bell (10-inch or more) bass trombones. Willie Berg invented Stonelined Mutes in 1935. This line of mutes has set the standard for performance over the years. No one knows more about mutes than these guys.