Uses M3 or M4 inserts to mount to HSW. Hexagons are 18mm across so should fit thicker pens like whiteboard markers.
4mm version will fit M3 and M4 screws. Larger slightly larger version included just in case.
You'll need 4x M3/M4 screws and 4x of the corresponding inserts.
The author remixed this model.
Pencil and tool holder for HSW