Sculptor's Calipers

The caliper tongs are symmetrical - duplicate the .stl in your slicer or print two of the same part to make the set. These are designed to be assembled using 1/4-20 hardware, but 6mm metric parts should work ok, or you can modify the Fusion 360 file to suit your needs. If printed at full size, the overall length will be 288mm - so you'll need a printer with a fairly large bed.

Update - added tensioning dial (knob) for use with a square type 1/4-20 nut to be glued in after printing. I also glued the screw with a fender washer in place on one of the tongs, fixing them in place, and leaving the tensioner nut to move freely. Works well for locking measurements in place.