This is a simple pen/marker holder for fridges, with a hole to attach a magnet or a screw.

Magnets can be glued to the backside of the casing.

I had a large 6 mm thick magnet with a screw hole (as seen in the pictures) so I added a small tab that glues on to the pen holder, to keep it steady against the fridge door. This can be omitted if desired.