D&D Tracker Book with flexible hinge and custom inserts

As with the original, eight 6x3mm magnets are needed (6x2mm will work). The four hinge holes should be filed with filament, with a bit of glue on the end to hold them in place.

The modules fit tightly and you may need to lever them out with something. 

Update: Wheels are now captive and pins have been replaced with sliders. Modules are now looser and snap in and out cleanly. Sliders may need tweaking – filament expansion (some filament types) can make these fit too snugly.

A pair of hinges have been added to allow folding the cover underneath. I've also replaced the card slot with space for several tracking inserts. Inserts are included, along with blanks to make your own!