90 degree outside caliper

Both the large and straight jaws move together and always have the same gap, allowing you to use a ruler or vernier calipers to make the measurement of some awkward places without guessing.

I designed these to measure the thickness of my door panel with a cat flap in it; the cat flap is very thick and deep, so regular vernier jaws did not do the job

You could scale this up to use other hardware, default is a 3mm pivot pin:
105.8% = 1/8" (3.175mm)
133% = 4mm
166% = 5mm

I have provided a .step file if you would like to remix this tool (add measurement indexes, a locking mechanism or a spring perhaps?). Designed using the fantastic FreeCAD v.0.20.1

Added a ready to gcode file generated with PrusaSlicer for Prusa MK3's with PLA filament