This is a camera clip to mount a 14mm wide FPV camera / transmitter module to a 20 x 20mm flight controller board stack as sold by BangGood. These are advertised as 20 x 20mm which is the mounting centres of the board. The PCB is actually 25 x 25mm.

UPDATE : I originally had the camera angle at 30 degrees, but my son (whom I made this for) found this was too steep and had to fly too fast to get good forward vision. Accordingly, I've added .stl files for 25 and 20 degrees off vertical.

There is a bit of an overhang in the print - Use support if you need to, or if overheating is causing the shelf to deform put the post in the middle of the arms in your printing software to slow down the print.

To fit, carefully slide the arms forward onto the PCB assembly using the blade of a small screwdriver to stop them catching on the components. Then squeeze to clip them around the far posts.
There's a slight lip on the flight board antenna guide. Use a small screwdriver to prod the antenna into the channel and it will stay there. The camera module is a tight friction fit in the holder.