At first glance you may think this puzzle is easy , but beware as when you have it in your hand it doesn't seem un-lockable 

But the 5 pieces do come apart , putting them back together however is a whole new puzzle in itself

No force is needed and even if you can't solve it , it has an elegance all of it's own

This puzzle is rated as 5 stars out of 6  making it Difficult to solve