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I know that there are screws with these features and know how to distinguish them. What type of screws should I use? Usually there are screws on the right thread.

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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

2 Answers 2

Differences:

  • 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. –  User58220 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

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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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