"This flap is a nice design that is allows the fitment of 100mm round or rectangle ducting; by simply snapping off some plates when required for round. Fitted two of these externally no problems for kitchen and bathroom extractors. The flaps so far are doing their job well. I did hear a bit of chattering the other day in some strong winds; but they are at least still present unlike so many you see; this will only tell in time I guess."
"I bought this in brown in the hope it would contrast less than white against red brickwork and mahogany effect PVCu window frames. It was spot on! Looks like it 'should' be there and doesn't stand out.
Just as a note, this has claws for rectangular flat channel as well as round pipe, so it is versatile."
"I wish I had known that it can be modified by breaking off tabs to use rectangular ducting, I had bought and installed an adaptor and a length of round ducting. The outlet only locates on the ducting using some tabs rather than a proper flange so there is a need for silicon sealant to ensure all the exhaust air goes where it should do."