Why did this become the standard? Is there some logic to it or did it just evolve over time to become standard?
I think it’s true that a clockwise action on screwdriver or spanner is stronger than an anticlockwise one, for right-handed people, so it at least makes sense.
Just a WAG, really, but IMO it’s easier for a right-handed person to apply full power clockwise (“righty”) – which (again IMO…) would be more of an issue when tightening then when releasing a screw/nut.
I’d have guessed the opposite. I can apply more force from my right hand in an anti-clockwise direction. As loosening a screw/nut/fastener that has been in for a while is much harder (in my experience), it makes sense to have the most force applied in the “out” direction.
Now that said, on a screw, you generally have to push IN to get the screw OUT, so it doesn’t make much sense…
I suspect it’s an arbitrary standard. First, I don’t think most people are much stronger turning something one way or the other. Second, right-hand threads are used even in places where strength isn’t an issue (e.g. light bulbs and even most uses of nuts and bolts).
There is a big advantage to standard threads. It would be expensive (and frustrating) for everyone if, say, half of all threads were left-handed. Imagine if a plumber, for example, had to have two sets of each type of fitting. There’s a strong incentive to standardize on something. My guess is that some small group of people settled on right-hand threads early in the days of machining, and the rest of the world followed suit.
Note that left-hand threads are used for some applications, often when rotation might cause a right-hand thread to loosen. For instance, it’s common for one of the pedals on a bicycle to have left-hand threads (I believe it’s usually the right pedal, which rotates counterclockwise relative to the crank as the bike is pedaled forward).
Ei?
I thought it meant the direction of the twist. To make a screw tighter, you turn the screwdriver clockwise (to the right), to make it looser, you turn counterclockwise (to the left).
Nothing to do with handedness.
There doesn’t seem to be a consensus here, but the two may be related, in that (at least in theory) it could make a difference in ease, power applicable, etc… whether you’re turning the screw/nut clockwise or anti-clockwise, and the preferred direction may depend on handedness. My personal opinion (as posted above) is that a right-handed person will find it easier to apply full power when turning the screwdriver/wrench clockwise. Others seem to disagree, but that’s where the connection (and perhaps also the confusion) arise from.
Why do some bolts and screws have left hand threads?
Post #5?
I’ve noticed that a fair amount of these “flatpack, self assembly” units have for some reason started using L/H threaded screws/allen type fastenings.
Chrysler used to use left hand threads on the passenger side wheel nuts up until the mid-70s. Actually I just googled it and 1971 was the first year they used right hand threads. And it was really hard to remember this every time I had to do brakes on the '67 Valiant!
Floor fans are this way…you screw on the retaining nut counter-clockwise.
WAG: It’s because in Western culture, we associate movement towards the right with forward movement, mainly because that’s the direction we write (and read).
Actually it’s the left side. If the shaft is slightly smaller than the hole (i.e. there is some play), a clockwise circular rocking motion causes the shaft to rotate counter-clockwise. (Like those toys that are basically circular plastic gears within a larger circular hole, that let you draw flower-like patterns. If you make a clockwise circular motion with your pen, the inner gear slowly moves counter-clockwise.)
That’s most likely it. Up until the 1700s or so, screw threads were all hand cut, which meant that you had all kinds of variation in terms of thread pitch, diameter, depth, and the like. When the first screw cutting lathes were developed, I doubt that anyone would have thought about developing equipment which could cut either left or right handed threads, they would have gone with one system, and that would have been right handed. I doubt that anyone would have had a powered (either by water or steam) lathe that could be reversed, and the machines run clockwise, so right handed threads would have been the easiest to cut (you can cut lefthanded threads on a clockwise running lathe, but it’s not easy).
Don’t know how I missed it, but I did.
Leaffan, I had forgotten those fun Chrysler products; now that you’ve made me remember, I seem to recall Nash (American Motors) did the same thing for a while.
It because of the “right-hand rule” in physics. Make the “thumbs up” gesture with your right hand. The direction of your thumb defines positive torque in the direction that your fingers are curled. Thumbs up = positive = counterclockwise torque, Thumbs down = negative = clockwise torque. The same rule defines what direction the screw travels linearly when you twist it in the direction of your finger curl; screw it counterclockwise, the screw travels “up”, or unscrews, etc.
(hijack) By The way, one of my physics profs said that the saddest thing he ever saw was students using their left hand to to the right-hand rule while taking tests (because they were busy writing with their right hand)! (end hijack)
Left and right handed threads are sometimes used when systems are associated but need to be kept separate. In an Oxy/Acetelyne torch setup one hose has left handed threads and the other has right handed threads. I can’t remember which is which but this keeps you from hooking the oxygen hose to the acetelyne tank and vice-cersa.
Machinists use a similar rule for figuring out the X Y and Z axises on machines.
Likewise old-style POL fittings on propane tanks and hoses are LH thread. For propane, at least, POL (Prest-O-Lite) has been replaced by big coarse-thread RH ACME fittings that only need to be hand-tightened, and can’t be easily confused with anything else.