Ok, full disclosure. I wanted to include one type of screw only, but the holes in the devboard were just a wee smaller than needed for everything to be M3.  So PCB assembly screws are M2, and enclosure assembly screws are M3. 

Lately at the Lab we have been exploring the use of hex nuts for fastening, instead of screw inserts. In principle it should work, but it does require a bit of adjusting and this time around time was of the essence. So, I had to go for the old, tried and expensive screw inserts. These little beauties are easily inserted into the bosses, and when fastening a screw they expand and the knurled section holds on to the plastic walls. I recommend using heat to insert them for enhanced grip. It works better than glue.