A co-worker dropped off a small (key chain version) of this puzzle on my desk. I looked at it and thought with only 7 pieces, this should be a breeze. However, I soon found the puzzle very challenging due to the number of potential wrong solutions and the required order of operation during assembly. Anyway, his version was pretty fragile due to the size, so I thought I would scale it up.
More Info: http://www.instructables.com/id/Wooden-Block-and-Pin-Puzzle/
Version to Purchase: http://amzn.to/2z9nIQW