In order to countersink the plexi using a standard countersink bit before opening the holes up to accept the number 6 screws, I filed the threads of one to use for testing the depth.I laid the aft top skin out flat and made the backing strips for the rear window, word of caution hear dont drill the holes at this stage like I did because the thickness of the plexi means the holes need to be slightly closer together so they need to be drilled when inside the rear window. They did not go to waste though I clecoed them to the outside of the window and used them as a guide for making the final cut to the aft of the rear window.
