Two-Piece Locking Puzzle

A puzzling puzzle ;-)
The idea, is, of course, to separate the puzzle parts.
Even if you know what's inside, it might be a slight challenge ;0)

#Printing and assembly

##Prepare:
You will need:
4 metal (I used steel) balls about 9mm in diameter (slightly smaller shall work too)
4 pieces of metal rod ∅4mm (I used brass rod), each about 28-30mm long.

Sand rod ends so that they are rounded. Best done by chucking the rods in a lathe, but an electric drill will do nicely too.

##Printing
Stop printing at 19mm layer height and put the balls and rods in (the balls in the round open holes, the rods in the slot joining ball holes, two in each puzzle half). Resume print.

##Attention
If you print through, it will be impossible to assemble the puzzle!

If you can't stop the print mid-way, split the puzzle at about 18mm layer height and glue the assembly together after printing.