This is a large simple Bolt, the thread and bolt head (nut) are separated by a left hand thread.
The thread is hollow allowing for it to be used as a compartment.
The term lefty loosey, righty tighty doesn't apply here with the left hand thread.
There is a 1mm clearance.

Print dimensions are;

The thread is z=190mm x=94.62 and y=94.62

The bolt head (nut) is z=60 x=200 and y=173.39

You can shrink the dimensions down to 80% if needed.

Original model at thangs.com: https://social.thangs.com/m/809535