The .3mf file contains a set of 4 corner clamps ( 2 mirrored pairs ) to clamp the corners of a PCB and 2 mirrored straight clamps to clamp the sides of a PCB.

The .stl files only contain the corner and straight clamp in 1 direction, to get the other direction use the mirror function in PrusaSlicer. (also mirror the top piece)

Use M3 threaded inserts in the holes in the clamps to screw the top pieces into with some M3x10mm socket head screws. The slots are for an M6 threaded rod, use nuts and washers to secure the clamp to the milling table.

Print with 100% infill.