Had a small window, with a storm window, but no screen. Didn't really need a separate full screen. So modified the lower pane of the storm window to accept a glass or screen insert, using aluminum frame. The aluminum for either glass or screen is available at the hardware store. Measure, cut to size, assemble, and done. Had to modify the rabbet to accept the thickness of the aluminum. Held in place with a few simple turnbuckles. Easy to change. Works for me.