State of the art installation
In order for a flyscreen to work properly and have an attractive finish (taut mesh), the box must be perfectly parallel with the handle and perfectly perpendicular to the side rails, forming a 90° angle with them. This can be done by simply holding the box with one hand while inserting the relative side rails underneath it. Now the box will lean on the side rails, parallel to the support surface. If the frame opening is irregular or if there are any out-of-squares, with this simple trick, any resulting slit will be visible in the upper side after installing the flyscreen, allowing you to cover it easily with suitable products (silicone, gaskets, brushes, etc.) that can be found at any hardware store.