The Broan-NuTone 634 Steel Roof Cap is an easy-to-install vent for exhaust fans (bathroom, range hoods, rec room, home gym, etc.). This cap provides reliable roof top ventilation and features both a back draft damper and bird screen, preventing outside air from entering the home and birds or small pests from entering duct work. Compatible with 6" ducting. Not suitable for dryer venting. Built-in backdraft damper prevents outside air from entering home Built-in bird screen prevents birds and other small animals from entering duct work Durable steel with a black powder coat finish Easy to install in new construction, replacement, or DIY applications Compatible with 6" round ducting