A dark ring of epoxy around the screw holds a shortened M3 brass insert in place:
As it turned out, the original recess left only a few threads for the M3 SHCS, so the much longer screw wobbulated alarmingly. I drilled out the threads, turned the knurls off the insert, shortened it a bit, masked the pretty knurls on the aluminum ring, then glopped the insert in place while the Sherline held the screw vertical:
While I was at it, I added a thin ring of foam rubber under the knurled ring to keep it from clacking against the upper bushing.
Now I can’t lose the hex wrench when I take the thing out for Show-n-Tell sessions …