Many customers have asked us to create a simple insert for them to use in a sliding window for their Cat; We listened and heard you LOUD and CLEAR; Now available-for Cat lovers; A simple solution Pet Access Insert for your Cat's.... Simply place a small strip of hook into the upper track of your window and attach the top of the Pet Insert to it - then attach your flap to the bottom of the Panel and close your window. That's it! 1-2-3 and your done. Now your Cat's can come in from the cold and be safe.