My second CAD design. Having recently got an Intuous tablet on offer, I found the pen holder at the back of the tablet a pain. Since I have a steel-framed desk and had some strong magnets kicking around, I made a simple pen holder that magnetically attaches to my desk.
The original CAD files are public, so feel free to remix for whatever magnets you can find - I ended up glueing the magnet in place as the countersunk screw sat slightly proud of the magnet, causing the holder to spin, removing the screw fixed this. I would glue in a small neodymium magnet if you are planning to make this yourself - the magnet I used was taken from an old GPS antenna.
OnShape CAD files are here (sign up for a free account): https://cad.onshape.com/documents/162fccb4b8d0af5095a5c427/w/821dfae66d492b2eb8728bbb/e/0b29aff7a859cd6cab0495ff