One M3x30 screw + 2 nuts.
Open the holes with a 3mm drill.
Smooth and paint all parts as needed. If wanted, add lenses, grids or foils into the holders.
Insert Screw through the lens stems, add the spacer, then through the monocle body. Add the nuts and screw them against one another, creating a locked system.
Make sure the Stone Fitting is an interference fit with the monocle body.
Slip stone around stone fitting, than snap into position.
I added strap loops to the main monocle body and re-designed the lenses to have an “alignment tab” that can be used to flip them apart and more easily choose between them.
The author remixed this model.