My version of a circle drawing stencil/template. With default parameters, renders 1-28mm circles on a 1.2mm thickness template. Annotation dimensions are in mm.

I made this for measuring curve radius on real-world objects to be 3D-modeled.

I'm citing an earlier circle template design as a source of inspiration, but I designed my version from scratch in OpenSCAD. My SCAD file is attached in case changes are desired -- improvements welcome.

For other polygon shapes, see: https://www.thingiverse.com/thing:4727553