Broan 4" Wall Cap
This wall cap is for use with either 3 or 4" round duct (a 4" to 3" transition adapter is included). It has a built-in bird screen, and a spring-loaded backdraft damper. It is made of 24 guage steel, with a black electrically-bonded epoxy finish.
Dimensions: 6.5" square (including flange), 2.75" depth (from siding), with a 5" over length (including duct connector)