Windkat is available in a variety of popular sizes to fit most flue pipes, chimney pots and chimney stacks. Windkat for Flue Pipes comes in five popular sizes (for 5 inch, 6 inch, 7 inch, 8 inch and 10 inch flue pipes) and is installed by slotting inside the flue. Simply choose the Windkat size that is 1mm to 10mm smaller than the internal diameter of your flue pipe, thereby ensuring a snug and secure fit. We include a tube of heat resistant silicone to seal the fit. We can manufacture Windkat to virtually any size by special order. See the size Guide here