Fake screw for Geocaching

This is a fake screw which can be used as a logbook container for Geocaching.
In the nut, there is a pocket which can hold a circular magnet (1cm diameter, 2mm thick) if you put the magnet during printing (if you print with 0.2mm layers, you can make a pause after the 14th layer to add the magnet in the pocket). Then, the magnet will be trapped, and you will not need any glue to make your cache magnetic.

UPDATE:
I now own an Alfawise U20, and the head is in a metal cage, so the magnet is at