# Righty-loosey, lefty-tighty
**URL:** https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756
**Category:** Factual Questions
**Created:** [May 22, 2011, 4:46am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756 "2011-05-22T04:46:28Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@what\_do\_I\_type\_here](https://boards.straightdope.com/u/what_do_I_type_here)
#### Post date: [May 22, 2011, 4:46am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/1 "2011-05-22T04:46:28Z")
Fight my ignorance when it comes to fasteners. Do reverse-threaded fasteners exist, and why?
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### Author:  [@running\_coach](https://boards.straightdope.com/u/running_coach)
#### Post date: [May 22, 2011, 4:50am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/2 "2011-05-22T04:50:55Z")
The left side pedal on a bicycle is reverse threaded as pedaling forces will keep it tight.
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### Author:  [@friedo](https://boards.straightdope.com/u/friedo)
#### Post date: [May 22, 2011, 4:55am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/3 "2011-05-22T04:55:04Z")
Anything involving something spinning in a counter-clockwise direction will use reverse-threaded fasteners so they don’t come loose. The left bicycle pedal that **runner pat** mentions is an example.
Here’s a weird example: there used to be a problem with people sneaking into NYC subway tunnels and stealing light bulbs. So they started replacing all the fixtures with reverse-threaded sockets that took reverse-threaded bulbs that could only be ordered in bulk. That successfully deterred people from stealing them, at the cost of significantly more expensive custom light bulbs.
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### Author:  [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)
#### Post date: [May 22, 2011, 4:55am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/4 "2011-05-22T04:55:08Z")
Yes, they exist, generally for one of two purposes - to prevent coming undone due to their rotational situation, or to prevent people from putting together things that shouldn’t be put together. The left pedal on bicycles is an example of the first. With ordinary thread the pedal would work itself loose and turn itself out of the crank arm. With left-handed thread it tightens itself. Gas and propane fittings would be examples of the latter.
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### Author:  [@Joey\_P](https://boards.straightdope.com/u/Joey_P)
#### Post date: [May 22, 2011, 4:57am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/5 "2011-05-22T04:57:14Z")
The exist all over the place. Mostly in situations where the object is turning in such a way that it would loosen itself if it had right handed threads. For example the hub on my floor buffer has left handed threads.
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### Author:  [@AlsoNamedBort](https://boards.straightdope.com/u/AlsoNamedBort)
#### Post date: [May 22, 2011, 5:01am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/6 "2011-05-22T05:01:53Z")
Follow-up hijack: When did they all decide that right handed threads should be the standard? And why?
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### Author:  [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)
#### Post date: [May 22, 2011, 5:02am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/7 "2011-05-22T05:02:08Z")
> [@what\_do\_I\_type\_here](#):
>
> Fight my ignorance when it comes to fasteners. Do reverse-threaded fasteners exist, and why?
I read years ago (can’t find a cite though) that some of the Nazis more secret weapons had anti-tampering devices that consisted of reverse threaded bolts or screws, a bracket, and a glass flask of poison gas. If the screws were turned the wrong way (which would be the right way for normal fasteners of course), the bracket would be bent and shatter the glass flask releasing the poison gas.
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### Author:  [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)
#### Post date: [May 22, 2011, 5:04am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/8 "2011-05-22T05:04:18Z")
> [@AlsoNamedBort](#):
>
> And why?
Probably because it’s simpler if all fasteners of the same size have the same handedness; you cut the number of fastener types you need to keep in stock in half.
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### Author:  [@AlsoNamedBort](https://boards.straightdope.com/u/AlsoNamedBort)
#### Post date: [May 22, 2011, 5:09am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/9 "2011-05-22T05:09:21Z")
> [@Der\_Trihs](#):
>
> Probably because it’s simpler if all fasteners of the same size have the same handedness; you cut the number of fastener types you need to keep in stock in half.
I meant why did they decide right over left. Flip a coin?
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### Author:  [@Joey\_P](https://boards.straightdope.com/u/Joey_P)
#### Post date: [May 22, 2011, 5:12am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/10 "2011-05-22T05:12:58Z")
> [@AlsoNamedBort](#):
>
> I meant why did they decide right over left. Flip a coin?
I would guess that it’s easier for most right handed people to turn something clockwise then it is to turn it counter-clockwise. Not as big of a deal when you have nuts and bolts with ratchets (a lever) but when you’re trying to put a screw into a piece of wood with just a screwdriver, anything to make it easier is a big help.
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### Author:  [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)
#### Post date: [May 22, 2011, 5:15am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/11 "2011-05-22T05:15:09Z")
Some older Chryslers had left hand thread lug nuts on the left side of the car, also for a similar reason that the rotation of the wheels could theoretically loosen the nuts. More commonly, the spindle nut that holds the wheel hub on the axle are sometimes reverse thread on the left side, as are some wheel bearing adjuster nuts.
I’ve always heard right-handedness is the convention because a right-handed person can put more torque on a right-hand screw than a left-hand one, and something like a wood screw is usually a lot easier going in than coming out.
ETA: Or what **Joey P** said!
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### Author:  [@dtilque](https://boards.straightdope.com/u/dtilque)
#### Post date: [May 22, 2011, 5:30am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/12 "2011-05-22T05:30:43Z")
Turnbuckles have to have one side reverse-threaded or they won’t work.
The hot water knob on faucets frequently is reverse threaded. I assume this is because it’s on the left side, so is usually turned with the left hand.
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### Author:  [@j666](https://boards.straightdope.com/u/j666)
#### Post date: [May 22, 2011, 5:37am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/13 "2011-05-22T05:37:39Z")
Oxygen gas ‘bottles’ have reverse threads for the regulators.
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### Author:  [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)
#### Post date: [May 22, 2011, 5:58am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/14 "2011-05-22T05:58:26Z")
I once saw a guy struggle with some sort of screw on a Soviet vintage [Lada](http://en.wikipedia.org/wiki/Lada) for 20 minutes (to adjust the seat, if you care) before he discovered that the threads were reversed.
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### Author:  [@Peremensoe](https://boards.straightdope.com/u/Peremensoe)
#### Post date: [May 22, 2011, 6:22am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/15 "2011-05-22T06:22:01Z")
nm
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### Author:  [@Jeff\_Lichtman](https://boards.straightdope.com/u/Jeff_Lichtman)
#### Post date: [May 22, 2011, 7:11am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/16 "2011-05-22T07:11:08Z")
> [@j66](#):
>
> Oxygen gas ‘bottles’ have reverse threads for the regulators.
Yes, the purpose being to prevent welding gases from being hooked up wrong. If you reversed the oxygen and acetylene it could be disastrous.
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### Author:  [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)
#### Post date: [May 22, 2011, 7:13am UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/17 "2011-05-22T07:13:55Z")
> [@GreasyJack](#):
>
> I’ve always heard right-handedness is the convention because a right-handed person can put more torque on a right-hand screw than a left-hand one, and something like a wood screw is usually a lot easier going in than coming out.
Err… something like a wood screw is usually a lot HARDER going in that coming out. :smack:
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### Author:  [@Hairy\_Bob](https://boards.straightdope.com/u/Hairy_Bob)
#### Post date: [May 22, 2011, 12:47pm UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/18 "2011-05-22T12:47:03Z")
> [@GreasyJack](#):
>
> Err… something like a wood screw is usually a lot HARDER going in that coming out. :smack:
Depends how long it’s been in. 😉
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### Author:  [@jz78817](https://boards.straightdope.com/u/jz78817)
#### Post date: [May 22, 2011, 1:24pm UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/19 "2011-05-22T13:24:11Z")
the '84 F-250 I had years ago had left-hand threads on the left rear wheel.
_Only_ the left rear wheel.
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### Author:  [@yabob](https://boards.straightdope.com/u/yabob)
#### Post date: [May 22, 2011, 1:33pm UTC](https://boards.straightdope.com/t/righty-loosey-lefty-tighty/582756/20 "2011-05-22T13:33:45Z")
International Scouts, at least during a certain period, had left handed lug nuts on one side, so International Harvester did it as well as Chrysler.
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