Here's an interesting part:
It's a bolt nut, which can be soldered into a hole on a PCB. The one on the photo is particularly interesting, because it's exactly 2.5mm high — same as the middle layer of my laser-cut acrylic case.
If I used those in places where I now use screws, there are several advantages. First of all, I use bolts, which are not self-tapping, can be screwed in and out practically infinite number of times, and don't put additional sideways stress on the top layer of the acrylic. Second, if I moved the holes a bit, and maybe added a few more around the buttons, I could get rid of the middle layer entirely — just have empty space there. That would halve the cost of the case.