Engineer's Puzzle

The Puzzle: Screwing with my brain!

This logic puzzle was first published in the US popular science magazine, Scientific American, in one of Martin Gardner’s regular brain teasing columns. It goes like this:

‘Two identical bolts are placed together so that their helical grooves inter-mesh as shown in the illustration. If you move the bolts around each other as you would twiddle your thumbs, holding each bolt firmly by the head – so that it does not rotate – and twiddling them in the direction shown, what will happen to the heads?’

Will the heads (a) move inward, (b) move outward, or (c) remain the same distance from each other?

Too easy? Why not email your puzzle to and put your wits against the intellect of the Engineering Materials’ readership?

Justin Cunningham

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