Hole Measuring Gauge for Calipers

Two of these caliper jaw extensions, fitted to your analog or digital calipers, allow direct measurement of the distance between two hole centres without any calibration or calculation. As demo-ed in my YouTube video:

This is the STL as used to print the parts in the video to fit my calipers on my Ender 3. The CAD model has the width of the jaw socket at 3.6mm although the caliper jaws are 3.0mm thick, so your mileage may vary depending on filament type, printer accuracy etc.

Link to OnShape model: https://cad.onshape.com/documents/927e7378937c50fa04b21cb5/w/6ce62e0a13c49e2474470450/e/bbef8aad1211814f22325255