These storage trays are for round threading dies which are used to cut threads on bars, bolts, etc. The trays stack on top of each other and are intended for storage use inside your toolbox.
Included are STL's for the common die diameters of 1 1/2", 1" and 13/16" (38mm, 25mm & 20mm). All the trays are the same size so you can stack any tray onto another.
I have included the STLs as well as the Freecad files (0.18.4) so you can completely customize them as you wish.
The author hasn't provided the model origin yet.