Feeler gauges for setting the distance between laser cutter's head and the material but can obviously used for other similar needs as well.
The ones in the photo have been cut from acrylic based on the svg but 3mf models are also included if you don't have access to a cutter and want to print them. Depending on the laser cutter and the material etc the end result might not be exactly X.00 mm but should be good enough for this use.
Made with Fusion 360, ParametricText plugin, Export to Origin plugin, Quas stencil font (some digits slightly modified in the resulting models)
Examples on the cover photo cut from 3mm acrylic on CM1690 laser cutter.
Added the whole set from 1 to 30mm.
The author marked this model as their own original creation.