I include 3 models here. Goal is clean, minimal and won't trap dust.
I first tried the larger model I provide here with strong magnets on the back to stick to my (metal backed) whiteboard, but the magnets would not hold. The metal is just too thin. I opted to mount to the wall with VHB tape, but I needed to break the design into 2 narrower models as pictured.
I provide all models. I imagine most people interested in this design would want the single model which holds pens and an eraser together.
The hole for the eraser measures 3"x1.5" (76mm x 38mm). Pen holes are 11mm which are just large enough for the narrow expo markers pictured. You may have to file them down a little if your printer isn't tuned well for bridging, but you want a snug fit so the pens stay upright.
STEP and Fusion360 files included so you can customize. No supports are needed. Print on the side.
The author marked this model as their own original creation.