Tiny holes in screens can easily be repaired with several applications of clear silicone glue. For larger holes in metal screening, start by cutting the hole into a square shape. Using a pair of tin snips, cut a square of identical screening and unravel half an inch of the edges of the patch. Bend these strands at a 90-degree angle to the patch and fit them through the holes in the screen, then flatten them out on the other side. Plastic or fiberglass screening can be patched by gluing a screening patch to the hole with silicone glue. If you need to replace the entire screen on a metal-frame window, you'll need a special tool called spline roller, which looks a lot like a wide pizza cutter. A spline is a piece of rubber or plastic that fits into a groove in the window to lock the screening in place. Pry out the old spline with a screwdriver and remove the old screen. Cut the replacement screening to the size of the outside of the frame, fit it in place, and then press in the new splines with the spline roller. Trim off any excess, and the job is done.