Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5877630.
Box in two parts that fit together, in the shape of a Lung.
With wall thicknesses of 0.8mm and a tolerance (space for interlocking) of 0.45mm.
Each part, prints, the side with the largest flat surface on the print bed. ( does not require any supports. )
In the event of a print bed adhesion problem, use a brim.
Suggestion to use a fixed Z joint position (X and Y point of the start of the layers), to facilitate post-print cleaning of possible print smudges.
It is preferable to take the time to clean and correct any printing defects (stringing or angel hair with a quick flick of a lighter flame, and cut or file small blobs and traces of Z join ...) to guarantee interlocking without risk of blocking.
If you have any questions or criticisms, or if you want another version (dimensions, or wall thickness, or nesting tolerance), please leave a comment.
Happy printing.
Credits : character code U+E25B from font "OpenDyslexicAlta Nerd Font Mono:style=Bold Italic" https://opendyslexic.org/