Maximize the air and sound performance of Broan ventilation fan or range hood. Footprint is 18-3/4" long x 14-1/4" wide for a well-balanced fit. Designed to fit with 3-1/4" x 10" or up to 8" round duct for flexible installation. A built-in, backdraft damper and bird screen provide a dependable roof cap. Roof cap is made of 24 gauge CRCQ steel construction with a black electrically-bonded epoxy finish for durability and long life. For use with Range Hoods, LoSone Fans and Bath Ventilation Fans.