How can you get these nuts off a double-headed bolt?
There's nothing complicated about a simple nut and bolt pairing, but this isn't your average nut and bolt. The "Nut Case" puzzle by Hanayama takes the form of an apparently unsolvable problem: two freely twistable nuts trapped on a bolt with a head on either side. There's more to it than meets the eye, of course, and if you know what you're doing you can not only free both of the nuts, but also use the whole mechanism to hide something small.
Mr. Puzzle gives a rundown of exactly what this puzzle appears to be at first blush and, if you're willing to have the mystery spoiled, what it really is on the inside:
The trick to disassembling the puzzle relies on not one but two hidden bits of unusual design, one on the bolt and one on the nuts. Spoilers ahead, so beware!