A sliding screen door doesn't do much good if it's left wide open by forgetful children, or adults with their hands full. Our smooth operating "block and tackle" mechanism will close it smoothly, automatically, every time, even if someone forgets! Horizontal, hollow aluminum bar (with tension cable) attaches to the screen door top rail and frame. Adjustable tension for variable closing speeds. Installs in left or right opening doors (36" wide or wider) with just a drill, level and screwdriver.