This is a printable 100x100mm Vesa mount plate for Dell stands that have the 4 screw holes pattern. It could easily be remixed to the 3 holes pattern by changing the location of the holes.

You will need M4 screws of 10-12mm length to screw the plate into the stand. 4 other M4 screws are used to mount the plate to the monitor. I used 16mm screw in this case.

(The 3 last photos are from eBay to show what the OEM parts look like).

Printed on a Printrbot Simple Metal, you need a printer that can do around 120x120mm to print the mount. I strongly suggest using support at the center.