Overall a very good Cat Flap which is resisting the breezy conditions today. Reading the reviews of other makes of flap and their respective sizes, I believe it was the best choice for our panelled door, despite the fact that it took some time to fit. The outer dimensions are the same as each of the panels on our door but, apart from cutting the hole, it was necessary to chisel out most of the beading around the selected panel, on both the inside and the outside, and this took some time. It wasn't possible to use the wide door fitting because of the moulding (beading) around the panel and to utilise the thin door fitting required a lot of chiselling to accurately fit both sides and to permit the longest screws to reach from one side of the door to the other. I had to dispose of the rubber seal to do this and because the chiselled wood was unlikely to be smooth enough for the seal to work. I may find that in very cold windy weather it will be necessary to pack the frame with some silicone sealant. It's also very difficult to align the screws blindly from the outer frame into the holes in the inner frame. I suspect that nuts and bolts, rather than screws would make this much easier. Despite all this I'm pleased with my purchase and it's working well. It's almost silent operation has not spooked our two cats and they are making good use of it, sometimes just to show off!