A friend posed the question on another board. Just to make it painfully obvious, I’m talking about how most screws tighten when you turn them clockwise as viewed from above. Left hand threads tighten when turned counter-clockwise.
I’d assume that right hand threads are the convention because you can hand tighten better that way when you use your right hand, but is the real reason and when did it happen?
According to Encyclopaedia Brittanica, screws date back to at least the 5th century BC and probably earlier. They probably originated in Egypt but there are no records as for why.
Jim Petty
An oak tree is just a nut that stood it’s ground
Jeremy…
I can think of no more stirring symbol of man’s humanity to man than a fire engine - Kurt Vonnegut
“right hand rule of rotational momentum”
if something is rotating clockwise (from the observer’s point of view),
it will naturally want to move away from said observer. Sounds like Mr. Lew had a screw loose left hand or right hand I don’t know.
There is that thing about elecro magnetism , electrons rotating or something where you make a fist.Seems like this is just a thing that became convention through use.
Right hand rules and all that jazz apply to charged particles moving through magnetic fields… And not to screw threads. Not sure where the convention came from, but its an arbitrary convention. The physics of a screw say that it makes no difference which direction you screw it in.
Jason R Remy
“Open mindedness is not the same thing as empty mindedness.”
– John Dewey Democracy and Education (1916)
Or it could be a very fuddled memory of gyroscopic precession. But, one way or another, it would have nothing to do with screw threads.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
There once was a fellow named Fred,
Whose… oops sorry
The right hand rule is associated with manny, manny physical phenomena. For an explanation of the right hand rule as it applies to mechanical engineering, see http://www.physics.uoguelph.ca/tutorials/torque/Q.torque.intro.html#RHR
The main point is
but check the website for an illustration.
To further explain (or confuse) things: Refer to Figure 2 in the above link. Imagine that the pivot point (yellow dot) is a bolt and the the beam of length ‘r’ is a wrench handle. The right hand rule tells you the direction of bolt torque (and direction of bolt movement - in or out of the screen) based on the direction of the applied load. This would be so much easier to demonstrate physically.
I’m assuming that the fact that a typical screw moves in the direction of applied torque isn’t a mere coincidence, but correct me if I’m wrong. If you have any questions, come see me after class.
OWWWWWW ,Strainger, now my brain really hurts. But why clockwise to tighten?
I may have figured it out. No one could come up with a catchy alternative to “Righty tighty, lefty loosey.”
Sorry about your brain, mr john. It’s tough to describe verbally. The most effective way to demonstrate the right hand rule would be to make an *.avi file of it (complete with narrative and visuals) and put it on a web page. Unfortunately, I don’t have the resources for that.
And, yes, I apply the right hand rule at work. One of the few and proud.
Strainger, don’t worry bout my brain I try not to use it too much anyway. I apply a right hand rule at work too, the righy tighty one. Well, really I generally switch to forward or reverse on the Makita.
Engineer ,ey? I am the one that has to build the stuff yall come up with. One of the tired and frustrated.
I can’t believe no one has yet pounced on Strainger’s remark that Mr. John’s brain is difficult to describe verbally.
wink
Live a Lush Life
Da Chef
What a screwy thread
(had to be said)
Sorry guys. You walk away from the PC for a couple of days and you miss everything 
I think that the right hand rule in physics is a convention derived from how the two vectors (lever arm and force) multiply; the cross product will be at right angles to both in the specified direction.
The electromagnetic right hand convention (again, if I remember correctly) relates to the direction of magnetic flux with respect to electron flow within a coil and was used for quite a while before it was proven that mankind had been lucky and got things right on this one. It doesn’t have anything to do with threaded screws unless there is a subatomic reason why most people are right-handed (and wouldn’t this be advanced research )
All, thanks for the input (bad puns included.) If it could be proven, I’d still lay money that right hand threads are the standard because a right hander can exert more torque (for comparison, note how when using a crescent wrench, the handle leads the motion; too much force in the opposite direction and the wrench will break or round the flats of the bolt or nut.) It looks like the reason for right hand threads will remain lost in the wastelands of conjecture.
Actually, there are common uses of left hand (counterclockwise = screwing on) threads. Usually, when they’re holding on something that’s rotating.
For instance, if you have real wire wheels on your car that screw onto a single center hub, the big screw cap that holds the wheel on will be reverse threaded. That way the rotation of the wheel tends to tighten rather than loosen the nut.
If you take apart a common home tabletop fan to clean it, you’ll usually discover that the nut in the center of the fan holding it on is reverse-threaded. Again, to prevent the rotation of the fan from “unscrewing” the nut.
So clearly, there’s no reason a reverse-thread can’t work just as well. I think it’s simply a matter of more people being right-handed and it being easier to exert more force to screw on a right-threaded nut with your right hand (and vice-versa for left-threaded. If most people were left-handed I bet “reverse” threading would be the standard).
cornflakes, the right hand threads are related to the right hand rule as used mechanically. There is a right hand rule regarding magnetic flux, but that doesn’t play here. (You’re right about the right hand rule being used to determine direction of the cross product). If you look at my first post in this thread along with the link. You’ll see that T = F X r where
T is the torque
F is the applied load
r is the lever arm distance at which the load is applied
A right hand threaded bolt moves in the direction of torque, i.e. it follows the right hand rule.
Whoa!! My bad. I meant that T = r X F. Yes there is a major difference.
“…the right hand threads are related to the right hand rule as used mechanically”
Are you sure? I assumed that the right hand rule is a post-newtonian concept. Furthermore, I was under the impression that threaded shafts have been around since the Egyptians, Sumerians or Early Greeks and I assume that they had right hand threads. Why?
The ridges on the conch shell in my bathroom form a right hand screw, but you have to rotate the shell in a left hand fashion (counterclockwise as seen from the top) to pour water out of it, so I doubt that they were modeled after nature. The early threaded fasteners were probably used in static applications, so the thread direction didn’t matter, as it does in moving assemblies; maybe it was just the natural direction for the workers to turn something after having used earlier mechanisms (windlass, touniquets, etc…)
It has been my experience that it is usually harder to UNscrew a tight bolt than torque one down. So to make it easier on a righty shouldn’t the threads be reverse? You need to avoid crescent wrenches if you can they do rond um over. But to turn the other way you flop the wrench.
Post Newtonian? Well the rule or law that explained a phenomenon that had always been around. If there is a physical reason the reason would have been there before any one knew why. Things fell down before Newton so people propped um up.
Strainger I still don’t see how that applies to the direction. Wether you are turning left or right doesn’t the same formula apply? It seems to be more about the amount of force applied by a lever of a given length, not direction.
For a while I was thinking it had something to do with the way screw cutting machines work . but actually it works better the other way.Lathe heads are on the left to accomodate righties and it seems it would be easier to move the cutter away from the head. BOING!
Just popped into my brain. Cutting threads to RECIEVE a screw, (making a nut),(no rude comments) you turn the tap clockwise. For a righty it is easier to control the force and precision pulling with the right hand than the left. Isn’t it? maybe
I tried to type a verbal description of my brain but it just made it hurt more. I would send a picture but I can’t fit my Kodak to the microscope.
This new BB setup is really messing with my head.
Cornflakes, you bring up some good questions - most of which, unfortunately, I can’t answer (although I’ll research as much as I can on my end):
Do right hand threads follow the right hand rule? Yes (This is the only question I can answer at this time)
Were right handed threads refered to as “right handed threads” before the right hand rule was discovered? I don’t know
Who were the first people (civilization and time period) to use bolts/screws? I dunno
Were the earliest bolt/screws right hand threaded, or did they even have a standard? Don’t know this either
I think that about sums up what we’re looking for. I’ll research these questions and let you know what I find out.