Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:6032013.

Holds 12 dry erase markers, in a horizontal position (intended to keep the tips from drying out). Length is such that caps protrude for easy color selection.

Holes/countersinks for mounting are intended for #6 wood screws. Marker bores (18.5mm) are sized for standard Expo brand markers (~18mm). The draft angle on the markers make for a snug, but not overly tight fit.

I printed mine in PETG @ 20% infill. Although suitable for PLA, probably better suited to materials with a little bit of compliance in them.