Measuring-Corner Joint Detail 

You will need to cut four pieces of screen repair extrusion. Two (2) pieces for the top and bottom and two (2) pieces for each side. The pieces should be cut with the measurements corresponding to (A-B) and (C-D) as indicated in the graphic.

Normally the top and bottom pieces should be the same length, but not always, because sometimes a window is not perfectly square. The same goes for the side pieces. Test fit your pieces to make sure they will fit 

To make the corner joint the top and bottom pieces must be cut shorter than the actual measurement (A-B) above. 

Shorten the actual measurement by approximately 1/2 inch-or twice the thickness of the extrusion-to allow it to fit inside of the side pieces, as indicated in the diagram at (A)

When completed the joint should look like (A) in the graphic at left and the spline grooves should align. This joint is just a butt joint with the extrusion ends cut straight and square. Aligning the extrusions provides a continuous groove for the retainer spline.

The blue line (A-B) represents the spline groove

C is the corner angle represented by A in the graphic above.

D is a cross-sectional view of the screen repair extrusion showing the spline groove