This is a mount for the RepRapDiscount Full Graphical LCD Controller for the Ender 3.
It was designed to be adaptable and for the LCD to be at a 90º angle, and be able to take out the LCD from the machine (to be used in an enclosure and keep the LCD out). The SD card can be accessed easily too...
2x M5 at 20mm or 25mm length to attach to the frame
2x M5 at 25mm length + 2x M5 nuts, to secure the corner