This Gator Black Bell Cover with Merv 13 Filter for wind instruments that have a 8 to 9' diameter bell. This cover fits the Trombone, Baritone Saxophone, Baritone Horn, and Alto Horn. Made from woven polypropylene fabric, it features a double-layer cover and a replaceable MERV-13 Filter to protect from aerosolized droplets from being expelled without significantly affecting the sound of your instrument. The bell cover is secured by an elastic closure and cord lock, which allows you to hand wash the cover (do not wash the MERV-13 filter).