I needed a Raspberry PI 3 case that is compact and robust, and stumbled upon jayftee's thing, http://www.thingiverse.com/thing:1427797. Great!
But I soon found out that I didn't have any M2.5x20 screws at hand, and they are not easy to come by. Thus, I modified the case to fit the M2.5x16 screws I could procure. The bottom part is only slightly modified (the nuts are set a little deeper into the casing), for the top part I had to thicken the screw bosses near their base.
This case works for M2.5x16mm screws, but the top part now should be easy to change to fit any screw length between 10 and 20mm.