The holder is currently designed for pens with a radius of 7mm and a round magnet (5mm x 3mm). It fits for most of the typical pens. If not you can change the sizes easily.

Its a fucional tool, because you can attach your pen where ever you need it. For example I have got one on my music stand, to correct my notes quickly if its needed.

You can get creative and use it for other objeckts too.