Broan Steel Roof Cap for 3-1/4x 10"up to 8" Round Duct Footprint is 18-3/4-inch long x 14-1/4-inch wide for a well-balanced fit Designed to fit with 3-1/4-inch x 10-inch or up to 8-inch round duct for flexible installation A built-in, backdraft damper and bird screen provide a dependable roof cap you can count on 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, loosen fans and bath ventilation fans