copper rooftop exhaust vent cap with damper and bottom extension (8 inch) generic this rooftop exhaust vent cap is designed to be used with bathroom and kitchen exhaust venting systems. this is a roof mounted vent cap that comes with a damper to prevent back draft, and also with a screen to keep out insects and birds. this product is made with heavy-duty copper. it also comes in a variety of sizes to fit pipes ranging from 4-inch up to 10-inch diameter. this model contains a metal bottom extension for connecting to flex tubing.