The complete guide
Using flyscreen corner pieces and wind clips
What this is and how much you need
One set is four corner pieces and two wind clips. A rectangle has four corners, so one set makes one screen. If you are building three screens you want three sets, and that is the only arithmetic involved.
It is almost always the second thing people order. You buy one large screen, then look properly at the house and realise you have four small windows rather than one big one. The material is fine. What you need is a way to turn it into the screens you actually want.
How the corners work
The frame is flexible PVC, sold by the metre. You cut it to the length each side needs with a sharp blade or a strong pair of scissors, and push a corner piece into each join. That gives you a rectangle sized to the window in front of you rather than to a box someone packed in a factory.
They push in rather than glue in, which means a screen can be taken apart and rebuilt at a different size later. If a window changes or you move house, the material is not wasted.
The wind clips
These are the part that gets skipped and then missed.
On a sheltered window you will never think about them. On an exposed one, wind pushes the middle of the screen away from the frame, and the moment the screen bows there is a gap down the side. Insects find gaps. That is the entire job they do.
Two clips is the right number, placed where the unsupported span is longest. Fit them at the build stage rather than deciding later, because getting to them afterwards means taking the screen off the window.
Getting the colour right
Order the colour that matches your frame, not your window.
The corners sit at the outside edges of the screen where you look at them every day. A white corner on a brown frame is exactly the detail that makes a careful DIY job look like a rushed one, and it costs nothing to get right because all three colours are the same price.
What else the job needs
A complete screen from parts is: frame by the metre, one corner set per screen, mesh, and a fixing.
The fixing depends on which kind you are building. A magnetic screen wants magnetic strip, sold by the metre, stuck around the window frame. A velcro screen wants hook-and-loop tape instead. Mesh comes in three grades, so you can put pet mesh on the window the cat uses and standard grey everywhere else without buying two full screens.