Pencil Holder that fits a triangle ruler (Geodreieck)

I wanted to have a pencil holder where the pencils can not move too much. So I can always pick a specific pencil. I also included a slot for a triangle ruler, that never fitted my old holder.

If the height is not the right one for you, I included my FreeCad File where you can just adjust the height by yourself. For the sake of simplicity, I also uploaded a 50mm height version, if you are comfortable with a lower version.