Based on your location it seems like you might be looking for the Canadian site.
Would you like to continue, or switch to the Canadian site?
Ducts, Dampers, Adapters & Caps
Broan-NuTone® Steel Roof Cap for 6-Inch Round Duct with Backdraft Damper and Bird Screen, Black
The attractive Broan® 634M roof cap is the perfect finish for your ventilation system. The built-in back-draft damper eliminates cold air from entering the home. The bird screen stops unwanted visitors from gaining entry.