Customisable parametric standoff spacer

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.