My students often use paint pens to add color to our prints, so I thought I'd make a Gridfinity holder for the markers.
Holds 12 markers that measure about 10.5mm wide.
They are far enough apart to grab individual markers without issue!
The author remixed this model.

I used a 1x2x6 bin as the base of this design. Reworked and changed using Tinkercad.