This is a handy stencil for basic shapes that can be placed in a Circa Notebook. It is just a little bit thick at 1.4 mm, but you can customize it, of course, if you wish. I also included a Circa "blank" template which you can use out on Tinkercad to create your own shape stencils.

The sample you see in the images was printed on a Creality K1 printer.

STL files and images are included.