I have a cheap AOC monitor that uses a pillar into the stand to hold itself up, and has no VESA mounts. I am not wanting to replace it just yet so this is a solution to that problem. 

You will want to have good layer adhesion to print it flat, as the stresses will be along layer lines which isn't super ideal but I didn't want to print it stood up.

It uses M4 nuts to go into the slots as that is the VESA standard.

I printed in PLA but PETG is probably a better option, 0.2mm layer thickness and 20% infill. I also increased perimeters to 3. You don't need supports I added a 0.2mm breakaway layer at the top of the screw holes.