Hanayama Cast Puzzle, purchased from Amazon.com, 2018.
(metal, 5 pieces, 1+7/8 inches long, nut heads are 1 inch between faces)
The little nut is not important to the puzzle;
it is just something to store inside.
both big nuts will thread all the way onto the two pieces.
But to take the puzzle apart,
the two pieces must slide apart when the missing threads on the big nuts line up exactly.
There are some false seams so that the body appears to have 6 equal sections,
when there are really only 4 sections.
The puzzle is made quite difficult because it cannot slide apart all at once.
irst things have to be lined up exactly to slide a bit and then exactly another way to slide further.
After two such steps the nuts come apart enough to get the little nut out,
but two more steps are need to get the pieces all the way apart.
One approach is to start with the big nuts close to each end for the first two steps,
and then closer to the middle for the next two steps;
for each step,
hold one end leaving the assembly hanging down and gently turn a nut to feel a slight release.