The Broan 634M Roof Cap helps you maximize the air and sound performance of your Broan ventilation fan or range hood. It's designed to fit a 6 inch round duct and a built-in, back draft damper and bird screen provide a dependable roof cap you can count on. It's made of 24 gauge CRCQ steel construction with a black electrically-bonded epoxy finish for durability and long life.