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I have just started learning about screw gauge and I came across this statement about pitch

The pitch is the distance between two consecutive threads of a screw which is equal to the distance moved by the screw due to one complete rotation of the cap.

I don't understand why it is so. Please explain in simple language.

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  • $\begingroup$ All my searches for the term "screw gauge" lead to pages about micrometers, or tools for measuring the diameter of a screw, rather than features of a screw thread itself. Are you actually asking about the thread pitch and lead? $\endgroup$
    – The Photon
    Commented May 4 at 13:50
  • $\begingroup$ yes, in the book that i am reading, this statement is abt the pitch. $\endgroup$ Commented May 5 at 4:25

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Consider a screw that has been partially driven into a block of wood. The screw has cut a thread in the wood and the when the screw is rotated the helix of the screw itself remains in the precut helical channel in the wood. If we were to mark a point somewhere on the helix of the screw itself, then after one complete turn that marked point and the screw itself, will be displaced by the distance between two successive threads. When looking along the axis of rotation of the screw, the marked point will complete a full circle, but it will not return to its original location in three dimensional space, because it follows the precut helical channel in the wood, because that is the path of least resistance.

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    $\begingroup$ It might help to just try this out and see how it works. Mark a spot on the threads with a pen. Hold the screw in your fingers with the mark facing up. Put your thumbnail in the groove just below the mark. Rotate the screw one full turn so the mark comes back up to the top. The mark has advanced one screw thread. So has the whole screw. $\endgroup$
    – mmesser314
    Commented May 4 at 14:19
  • $\begingroup$ @mmesser314 That concurs with what I was saying. Its actually quite hard to describe, but your example is an easy way to provide a practical demonstration. Thanks :-) $\endgroup$
    – KDP
    Commented May 4 at 14:33

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