A remix of @Doctor_H's bases with the number chopped off, the back notch removed, and the overall size increased slightly to improve the fit.

The blank pad will allow you to paint or sticker on whatever you want after printing, which I think will be more scalable beyond 9 units.

I found that the original design fit units much too snugly, making it difficult to insert and especially remove them without damaging the plastic. I've learned that official aero units have the largest hex bases of anything I own, so the minimum size of these markers have to accommodate them specifically.