Older windows with wooden frames may be trickier, and the corners won’t always be square. If possible, use the original screen to obtain dimensions for your new one. Otherwise, use your best judgement.

Take note of the spline groove on the screen frame—the width should be marked on the packaging. When you purchase your spline, it needs to match the width of the spline groove. If you’re re-screening a window and the screen frame is still in good shape, you can use that instead of purchasing new framing. Just make sure to keep the black spine that goes around the old screen, since that is what holds the screen in place. [3] X Expert Source Michael FoxWindow Repair Specialist Expert Interview. 1 December 2020.

Buy hacksaws from home hardware stores or online suppliers. Check the TPI on the product label or manual.

If you don’t have a vice grip, place each bar onto a clean, flat surface. With the edge to be cut hanging from the surface, have a friend hold the other end firmly as you carefully saw the bar. Always exercise caution and cut away from you and anyone helping you.

Never file in back and forth motions. Whenever possible, secure your aluminum in a vice grip to keep it stable.

Make sure your corner inserts are 1. 5 inches (3. 8 cm) long. Purchase them from home hardware stores separately or in window screen packages.

Compare the width listed on the spline packaging to the width of the spline groove listed on its packaging.

Have a friend hold the frame steady as you pull the screening over the surface for better results.

Don’t worry about cutting completely straight—giving yourself enough extra screening material is more important.

When using a spline roller, always make sure the legs are aligned with the channel and don’t come loose as you move. Press firmly down onto the mount to keep it steady as you drag the spline roller through the frame channel. Pull the screen material tightly away from the frame as you move the spline roller.

Press firmly down on the roller as you move along the channels. This will wedge the screening into the frame. [14] X Expert Source Michael FoxWindow Repair Specialist Expert Interview. 1 December 2020.

Apply a firm amount of pressure down on the knife when making your cuts.

Be sure the spline is firmly connected to the aluminum frame before installing it in your window opening.