Update 1: Added 5mm and 8mm feet
These feet are made to rise the case from the surface with 3/5/8mm.
In case there is a bottom mounted fan, this could increase airflow.
The holes should guide a M3 screw with ease.
As this is a spacer, we'll use the thread of the feet to tighten te screws.
I used 8mm M3 screws that I had lying around for the 3mm extender.
Haven't tested screws for other feet.
Basic screws are 5mm, just add 2 - 3 mm and you should be fine.