I added the label ‘millimeters’ on the side.

This is meant for a quick glance at what each thickness looks like. Its one thing to see it in CAD, but another to see its dimensions in reality. This is 1mm through 10mm. There is an extruded square, a negative space square, an extruded circle, a negative space circle and an open ended gap.

there is a hole in the top corner to hang this on a pegboard.

You can print it in different orientations and with different filament to get a fill for different filaments and types.