A friend recommended a Finger Wrench and it looks useful, indeed:
That’s a 10-32 socket head cap screw, on the large end of the screws I normally use.
The orange PETG required a bit of smoothing around the overhangs, but should work well enough. The dark tinge near the bottom comes from the black filament I used for the MPCNC’s Z Axis sensor and won’t affect its operation in the least.
Done with one perimeter thread and a 3 mm brim to glue down the bottom:
That was easy …