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® Aluminum Wall Cap, 6-Inch Round Duct
Select the Broan-NuTone® 641 Wall Cap to provide reliable wall ventilation. Features an aluminum finish and is designed for use with 6" Round Duct. Includes a built-in back-draft damper, and protective bird screen to prevent small pests from entering duct.