These are inserts and knobs for a dovetail clamping system. The inserts are placed in the dovetail cut, and the knobs are used to tighten them down. These can be used to position stop blocks, secure fences, and so forth.

These require the addition of threaded inserts and 10-32 machine screws. Threaded inserts are set into the knobs and one of the inserts. The other insert has a machine screw inserted into it. Holes are sized for using heat-set threaded inserts. For the insert that uses a screw, it's sized for a flat head 10-32 screw with a 82° angle.

You can get these from McMaster-Carr:

Threaded insert: https://www.mcmaster.com/93365A154/

Screw: https://www.mcmaster.com/catalog/127/3289

Note that for the screw, you can select any length you want, but it should be 10-32 and should have the 82° angle on the head. Insert both the screw and threaded inserts by heating them with a soldering iron and pressing into place. Make sure the piece is straight and flush. The screw may push some material on the insert out of shape, but don't worry; it will still work in the dovetail channel.

Orient as necessary to avoid supports for printing. Note that for the dovetail pieces, the small chamfers should be oriented up. If you do it the other way, the pieces will most likely pop off the print bed during printing.

Draft settings on a MK3+ seem to work fine. No need for super fine resolution on a workshop piece.