When a screw head is recessed and that side must be down on the 3D printer bed, the inner hole for the threads ends up with its perimeters floating in mid air and will fail. Support sucks and especially so inside a hole/recess. So the trick is to trick the slicer a bit. Add a recess inside of the recess so only valid bridging happens. Very cool trick although it’s pretty easy to just add a single layer across the inner hole and drill it out quick like after the fact.
