4" x 4" Inch Brown Air Vent Cover - Steel Return Air Grilles - for Ceiling and Sidewall - HVAC - with Insect Protection Screen (3.93" x 3.93" inch, Brown) - - Amazon.com
Map Vent Fixed Louvre Vent with Flyscreen Black 145mm x 145mm - Screwfix
Xpelair Gas Louvre Vent Stainless Steel 189mm x 126mm - Screwfix