Here is another container like a "screw".
But its a fake to hide something inside (like a geocache logbook).
On the nut side is a cut out, to place a magnet Dm 10mmx5mm with clue.
If the magnet is placed you can put the screw on steel metal things.
Uninitiated persons only see a screw.
-Print it with a 3D Printer and PLA.
-With support material
-Layer height 0,25mm
-Volume ~55mm x 35mm outside
-Remove support material
-Deburr with abrasive paper
-Sprayed with silver colour
-Glue the magnet with hot glue.