I needed some spacers to create an air gap for cooling a Raspberry Pi being mounted behind a unit. I'd printed one of these cases which, as the designer comments, won't actually let air through the bottom slots - https://www.thingiverse.com/thing:4785712
Searching on Thingiverse didn't quickly turn up something suitable, so I put together a simple design in openSCAD.
It's easy to change the parameters in the .scad file to make spacers that will fit any specific application. But beware - if you put strange values in, you'll get strange results out.
The .stl file will print four spacers, 6mm high to fit over M4 bolts.

Prusa

I3 MK3S

No

No

0.2

10%