Saturday, August 6, 2011

Wrong Way Nut

A moderator on my favorite puzzle-building forum called attention to a YouTube video entitled Magic Nuts and Screw Threads in which two nuts are shown unscrewing in opposite directions on the same threaded rod.
I don't have any inside information about the trick nut in the video, but I conjectured I could build a nut that would behave like that. The threas on my first test model turn a bit tightly, but it works!

I will record a better demo video later. It could use a little refinement, and the screw threads need to be a lot longer for a better demonstration. But it's sure gratifying when a new idea passes the proof-of-concept test on the first try!


  1. Holy crap man! I am racking my brain trying to figure out the secret to this!!! Would you post a stl file?

  2. I will probably post the STL files after I've explored a few variations and picked the best design. Bear in mind my bolt has unconventional threads, although they look fairly ordinary. Frankly, I'm afraid the actual solution might be disappointingly prosaic!

    I promise there weren't any sneaky tricks, but this particular video has flaws: the bolt and nuts go out-of-view several times. But the last section honestly shows how both nuts behave on the same bolt at the same time.

    I will post more pictures soon!

  3. Scott:

    Very cool that you were able to build it. I don't know how the original works, but you might be right about "continuous" suggesting "conventional" but not actually meaning "just like a real bolt." Those deceptive, weaselly words are everywhere...

    -Bob, from Deceptology

  4. I think I have it figured out now. I was hoping for some kind of magic nut that could spin backwards on any bolt. This is more of a magic trick than an engineering feat. Still very cool though.