OX Pen Holder

Pen Holder inspired by: http://www.thingiverse.com/thing:261162

You can find my CAD model in OnShape: https://cad.onshape.com/documents/1ab6b066f6d94400916b30d8/w/7a68bf29b63d4e1e9209e5da/e/2a07b34b57cf4736a098dee9

This variant can hold pens up to about 15mm in diameter, and has a recess for an M3 nut.