This puzzle was designed in the 1970's by Stewart Coffin. It is notorious for being very difficult despite having only three fairly simple looking pieces. This version is made from 13mm cubes, and one piece has a hole in it so you can hang the completed puzzle on a chain. Wood versions of this puzzle tend to break easily due to the quarter face joins (unless they are doweled). The fit is usually excellent on these plastic versions, it should not fall apart when hanging by the chain.