Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5196767.
These are a remix of the famous geocache (hanging micro) by bfabry Many a model have had these threads pushed into a model to make a container. But, the knurled insert always protrudes from the bottom (or doesn't in some bad examples like https://www.thingiverse.com/thing:2960437 for instance)
This allows you to push in a flush opening that will screw in completely flat on the bottom
In order to insert this into a model you put a hole cylinder 35.3mm x 35.3mm x 30mm tall into the model, Then grab one of the 2 threaded portions and insert, and include the log holder.
For geocaching this is the equivalent of put a bird on it
This object was made in Tinkercad. Edit it online https://www.tinkercad.com/things/hd0Np5EWw1J