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I know that there are screws with these features and know how to distinguish them. Usually there are screws on the right thread.

When and what type of screws should I use?

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Generally speaking, every screw you will encounter or should use in a "household" context will be RH threaded. I've only used LH screws in automotive/bicycle/industrial machinery type situations. – whatsisname Nov 6 '13 at 17:32
Perhaps you could describe the application for which you would consider a LH thread? – Chris Cudmore Nov 6 '13 at 18:54
up vote 4 down vote accepted


  • Righty Tighty, Lefty loosey doesn't work with left-handed screws.
  • Right-handed screws move away from you if you rotate them in a clockwise direction, whereas left-handed screws move towards you.

When to Use Left-Handed Screws

When fretting induced precession would cause the right-handed nut/screw to loosen, a left handed nut/screw should be used.

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Chew tawkin 'bout rotational loosing, bub? – HerrBag Nov 6 '13 at 17:38
Chrysler products used LH lug nuts for years, but only on the left side of the vehicle – HerrBag Nov 6 '13 at 17:48
I read of a large transit system (NYC?) that had LHT sockets and light-bulbs to deter bulb theft. They were a huge customer, and it only needed a production line change in the pressed metal in the socket and bulb base. – DJohnM Nov 6 '13 at 19:00
I've found that sometimes the right hand (on the wrench) doesn't know what the left hand (thread) is doing. – mac Nov 7 '13 at 14:21
@HerrBag - It was all fun and games sitting back snickering with my buddy at one of our less informed friends trying to remove a flat until he put a swede on it and managed to twist the stud off. Dodge'm – Fiasco Labs Feb 20 at 3:26

Most common use is probably on a turn buckle. Think screen door sagging fix.

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enter image description here

you can easily distinguish right hand and left hand thread by visualize it.and it is depend on your need that what type of screw you can use for which purpose.

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