Broan 644 Roof Cap, 3-1/4" x 10", Silver 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 you can count o Roof cap is made of 24 gauge CRCQ steel construction in a .025 natural Aluminum finish for durability and long life For use with Range Hoods, LoSone Fans and Bath Ventilation Fans