This is a take-apart type puzzle similar to the Cast Cage and Aluminium Hedgehog, where the object is to remove the centre piece, in this case the inner brass cube. There is only one solution to the puzzle; the brass cube can only be extracted from one of the 6 open circular holes on one of the sides of the outer cube. Each of the circular holes have 4 tiny v-grooves cut into the sides. In order for the brass cube to be freed, the corners of the brass cube must fit nicely into the v-grooves for a smooth exit out of the hole. The difficulty is enhanced by the fact that the brass cube itself is not a perfect cube with equal dimensions (although this is not obvious), as the differences in lengths of the edges are approximately -/+ 0.5mm. Similarly the v-grooves for each of the 6 holes are also not all identical in their respective positions. As a result, there is only one correct side of the brass cube where all 4 corners will be able to pass through the v-grooves of the correct hole.
|Notice the 4 v-grooves cut into each side of the 6 circular holes|