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How can you get these nuts off a double-headed bolt? Split Anchors
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!
The double-headed bolt is actually hollow and made of two pieces. Each one has a pair of rectangular slices taken out of its cylindrical body. The voids of one piece match up with the protrusions of its twin, and that lets the two fit together as a single cylinder. The nuts, meanwhile, have gaps in their internal threading which means that when oriented correctly, they can slide freely when they're only on one half of the bolt instead of on both at once. Here's a picture help illustrate it, and there's a detailed solution at the end of Mr. Puzzle's video above.
There's not much room inside, so don't expect to hide anything much larger than a few screws or a smaller nut, but you can bet whatever is inside will remain secure from all but the smartest puzzle solvers.
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