My first Onshape design and probably my 4th ever design.  The original design fitted my Draper calipers.

Allows you to measure inside or outside of an object.  Varying degree of accuracy depending on the length of the Caliper extension and the length of the pin. For outside, it should be quite good e.g. +/-0.05mm as you can zero the calipers, but for inside (pins pointing outwards) it may be a little more off as you will have to measure the distance from pin to pin using a ruler or a second set of calipers and add to you measurement (on my prints the printed legs did not join in the middle when the calipers were closed (see pic), so measuring the leg to pin on each leg would not work as there is still a gap between the legs e.g. pin point - leg - gap- leg - pin point). But may be accurate to within 0.5mm or less if you play around a bit.  The bigger you go the less accuracy you will probably have. Better than nothing if you need a measurement.

You really need to have a calibrated printer (TeachingTech web site will help). I have used M5 threads and preferably you need an M5 bolt to “tap” the thread in the printed legs to ensure a clean thread for the pins.  Try to make sure when you tap, that the bolt is as perfectly vertical as possible to help “join the two pins together” when pushing the calipers to 0.  You could use M5 bolts as your pins if you like.  I was thinking of creating a pin with a hole to hold a cocktail stick (super glued in) to give a very thin pin if needed.  I may look at this and add it if people want it.

After creating the remix I either have an issue with the original design not quite fitting my calipers, or a slicer setting/flow issue that is making the legs not meet vertically correctly and introducing a gap between the legs.  But the print is still usable especially for the outside measurement.

I have included the STEP files for all the pins, you should be able to pull them into your slicer as most slicers today will deal with STEP files.

I used these settings to print the main legs.  Leave a comment if you have better ones for more accuracy.

Nozzle : 0.4mm

Layer Height : 0.2mm

Perimeters : 4

Infill : Support Cubic at 70% (bit quicker to print than Cubic and I guessed at 70%)

Brim : 5 (recommended to stop curing of the legs and I would say required for the pins - you may want glue stick too)

Supports : I used none and printed the legs flat on the build plate (see pic), but you could print them as per the stl if your printer will print vertically with ease, mine needed supports.