This model is designed to use four 8mm x 3 mm magnets (I bought mine on Amazon). The magnets are concealed within Base, kept in place by Casing. The "Clean" / "Dirty" letters snap into place (or glue them).
The tolerances are tight. If your calibration is off, you might have problems putting the letters into Base or putting Base into Casing.
See more of my designs at Thingiverse https://www.thingiverse.com/DorffMeister/about
CA glue (or insert) magnets into Base. CA glue Casing onto Base to conceal the magnets. Snap the letters into place (CA glue of necessary).
The author hasn't provided the model origin yet.