# Do screwdrivers defy the laws of physics?



## craftsman on the lake (Dec 27, 2008)

A question was asked of my years ago and it always stuck with me.

*Why is it that when you use a longer handle screwdriver you get more turning power?*

Explanation of question. If you have a ratchet with a socket on it and you need more torque you get a longer handled ratchet or add an extension to the handle like a pipe. With a long enough handle the bolt or the ratchet will break. The longer handle acts as a longer lever. With a screwdriver a thicker handle will do the same thing but also, as long as you can get a good grip, a longer screwdriver will give you a similar effect. Got a stubborn screw? Get a longer driver. Even with two screwdrivers of the same handle size and bit size, one a foot long and the other a short tight space one. The longer one will turn a tough screw easier.

To me, it doesn't seem to follow the mechanical advantage rules that we know of simple machines. There must be some explanation. I don't think the laws of physics apply to all things but screwdrivers. Then again, I ask myself, "Are there more important things to think about than this?".


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## Handtooler (Jul 24, 2012)

And, some of the larger screwdrivers have wrench flats just below the handle so one might get back into the physics realm by extending the leverage horizonially out the side, Huh?


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## deezldub (Apr 22, 2013)

The way it was explained to me (servicing Japanese photo processing equipment for 20+ years) the longer shaft screwdrivers allow you to keep more pressure on the tip by leaning into the screwdriver, and it builds up rotational torque to help break the screw loose. It would usually just "pop" loose with the longer drivers and once you got it started you were good to go, We were issued both 8" and 12" philips (JIS standard which are a tighter fit) # 2 drivers that worked wonders for getting chemically crusted screws to break free without camout.


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## bigblockyeti (Sep 9, 2013)

You can wrap your hand more completely around a small handle with a long shank given the distance you have between your hand and the work piece vs. having the same sized handle and a shorter shank. The psychological difference is there as well; you're less likely to bear down on a smaller handled screw driver (most also have a shorter shank) due to the likelihood you'll slip and hit your hand on the work piece. Metal can sharp, wood can be too and our sense of self-preservation tends to kick in and prevent us from hurting ourselves, especially when our experience tells us there's probably a better option.


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## renners (Apr 9, 2010)

If this was on "Call My Bluff" (a terrible British game show where three explanations are offered by eminent intellectuals to some obscure puzzle), I would go with answer 2, rotational torque advantage.


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## jonah (May 15, 2009)

The answer is that you don't get more turning power from a longer screwdriver. You get a bigger handle that you can apply more downward force and torque to.

If you had a stumpy screwdriver with a huge handle, you'd see the same effect.


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## Tim457 (Jan 11, 2013)

There was a post on the Lost arts press blog about this. From an 1880 magazine article or something, and a few engineers chimed in.


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## Tennessee (Jul 8, 2011)

This is like a "mindworm", something in your head you can't quite figure out. I've imagined the scenario, and you are right about length, but shorter screwdrivers usually have somewhat shorter handles, and your body and arm is more cocked, eliminating some torque. I'm not really buying that rotational torque thing, where the shaft might actually act like a spring, wind ever so slightly and then add torque.
Long handle, long arm torque = more advantage.


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## HorizontalMike (Jun 3, 2010)

I would suggest that the longer shaft has more flex than the shorter shaft. When turning the longer shaft, some of the energy you are exerting on the screwdriver by twisting, is stored as "potential energy". When the screw/bolt finally "snaps" loose, this "potential energy" is converted back to "kinetic energy" thus giving a longer (time) push/twist in loosening the screw/bolt. This can be interpreted by some as being more powerful, though the same amount of total energy is exerted in both short and long handled screwdrivers.

That's my 2-cents anyway…


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## joeyinsouthaustin (Sep 22, 2012)

I think the answer is based more in ergonomics than in physics…. Send you question into the Mythbusters!!


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## a1Jim (Aug 9, 2008)

It all seems "screwy" to me


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## Gene01 (Jan 5, 2009)

While I have benefitted from the same phenomenon, I have no answer as to why it works. 
OTOH, I can answer your final question: Probably, but where's the fun in that?


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## ZacD (Aug 1, 2013)

It has always been my impression that longer screw drivers also have larger shanks, and sometimes larger handles (this is apparent in your photo). So they would inherently carry more torque than shorter screw drivers, which typically have much thinner shanks. On another note, a larger shank is less likely to deform and twist against you and the handle holding it will also be less likely to deform and twist, because the shank has more surface area for the handle to hold.

The only other way it works is if it is in your head. Nothing has yet been discovered to defy any current laws of physics.


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## jumbojack (Mar 20, 2011)

It is another one of Gods gifts to man. Siphon is another that comes to mind.


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## Danpaddles (Jan 26, 2012)

I've broke a few laws in my life, but whenever I've tried to break the laws of physics, it never ended well.

If the longer shafted screwdriver works better, it is because the rotational force is closer to your body, where you can really put the torque to it.

No laws of physics have been broke. Now y'all move along, nothing more to see here.


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## CharlieM1958 (Nov 7, 2006)

I have often wondered the same thing.

I don't have the answer, but I do* not* believe it has anything to do with the bigger shaft/bigger handle/better grip theory some have suggested. I make this statement based on personal experience, and the five years I spent selling Craftsman tools part-time when I was in high school and college.

Take two Craftsman slotted screwdrivers. model #'s 41581 and 41582. They are identical in shaft size, tip size, and handle size, but one has a 4" shaft and the other a 9" shaft. The one with the 9" shaft will definitely turn a tight screw easier than the shorter one, even though all other factors are equal.

I believe HMike is sort of onto the right answer. I think the longer shaft flexes rotationally as you apply pressure, building up leverage. In other words, the force of the metal shaft trying to return itself to its normal shape is added to the rotational force applied by your hand.


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## pintodeluxe (Sep 12, 2010)

It is not just physics, but biomechanics. The hand is in a more neutral position when using a full-size screwdriver. There is also more surface area in contact with the tool. More surface means more friction and easier screw driving. 
From a pure physics standpoint it is actually the radius of the handle that determines the torque. T= F x D where distance is the radius of the driver handle.
But I always use an 18" long screwdriver just to be on the safe side.

Questions like this are great.


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## CharlieM1958 (Nov 7, 2006)

Just to clarify my hypothesis: I would agree, from a physics standpoint, that the shaft length alone would not make a difference* if the shaft were completely rigid*. I am thinking the longer the shaft, the greater the flex, and,thus, the greater the leverage. (Think in terms of compressing a spring.)


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## sixstring (Apr 4, 2012)

i'd say the longer screwdriver handle only provides additional leverage if used at a slight angle. that slight 1-2 degrees goes a long way towards providing extra torque and surface tension the longer the handle is. But, if you used different length drivers and kept it at exactly 90deg to the screw head, no additional benefit is gained.


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## wormil (Nov 19, 2011)

I don't believe there is any mechanical advantage to a longer screwdriver or at least none I've noticed. But I don't have any screwdrivers that are exactly the same except in length. If you really want your mind blown, add a piece of rubber hose pipe to your Crescent wrench or ratchet handle; not only will your mechanical advantage drastically improve but the tool will be more comfortable to use.


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## patcollins (Jul 22, 2010)

Lets say the optimal use of a screw driver is 90 degrees =/- 5 degrees. When wrenching on a screwdriver you are always going to get off of that 90 degrees, with the longer handle screw driver you can get off it by a larger amount but the angle is less than it would be for a shorter screwdriver so it helps you stay on target better.

My question is when you have to balance a screw on the end of a screw driver why does it not fall off until you get right up to where you need it, why didn't it fall off sooner?


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## racerglen (Oct 15, 2010)

Daniel, you are EVIL ;-) look what you started !
But seriously, I'm thinking the rotational force with the longer shaft makes horizontal sense ..
tnx Mike.. !


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## hobby1 (Feb 10, 2012)

When I use my 9" long shaft phillips driver, to tighten a woodscrew home, I notice the handle turns with the shafts rotational bend, while the screw stays put, I try to do that with my small shaft screwdriver, and its like turning a solid shaft no give anywhere, both screwdrivers havwe the same size handle and dia. shadft, just the longer one is able to be torsion sprung, sometimes I'm concerned I'll break the shaft on the long one with the amount of torsion spring that takes place.


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## longgone (May 5, 2009)

A longer shaft has a hidden *"mini" torque converter* secretly built into the shaft.
Oops…Sorry, I thought today was April Fools Day…


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## MrRon (Jul 9, 2009)

It is harder to keep the screwdriver tip perfectly normal to the screw head with a short shank. A longer shank allows you to maintain a more perpendicular address to the screw head without "camming" out. The other factor is the ergonomics of the handle. large handles permit a stronger grip than a small handle. Handles that have a non-slip surface also aid handle torque over handles with a smooth surface. Take a bicycle handlebar wit hand without a rubber grip as an example.


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## ZacD (Aug 1, 2013)

I also considered the idea that the slight angling of the driver could give an advantage, but unless you are giving the entire driver an axial spin around the screw (as if you were turning a horizontal crank wheel) it wouldn't be likely to give any advantage. It probably also won't hurt your overall potential.

Still, it has everything to do with the shaft being larger, or the handle being larger or some combination. That is simply how torque works.

Consider a stepped pulley in a drill press. Typically the difference in speed is several thousand RPMs and the torque will always be the exact inverse. It doesn't take much in the way of diameter to make a big difference.


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## Grandpa (Jan 28, 2011)

The longer driver does give more torque. Horizontal Mike gave you the correct answer. He is correct. It is like using a nylon tow strap to pull something out of the mud. The first couple of feet you travel is just stretching the strap. The longer the strap the more energy you can store in it. Then when the object starts to move you have the energy of the towing vehicle plus the energy that is stored in the strap. You twist the long screwdriver some for that advantage. Go gettum Mike!!


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## Dark_Lightning (Nov 20, 2009)

No. Physics is not violated in this case. Violations of Physics are generally based on lack of understanding of the observer.

The screwdriver on the left has a lot less hand-holding provision than the one on the right.

Maybe this really is a joke, looking for a punch line?

BTW, grandpa, that screwdriver shaft is going to wind up a whole lot less than the nylon strap will stretch. Like a million times less.

I design tools as part of my job. One of the tests I make is to take the prospective tool to a torque tester and make sure that the tool is sized for proper torque application in the available space. That will dictate the knob size and length, at the very least.


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## Underdog (Oct 29, 2012)

There might be some truth to the longer shaft, springy snappy theory…

But for my money, I'm gonna say that a longer handle makes all the difference for me. I just can't get a grip on the short handles of those stubby screwdrivers.


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## exelectrician (Oct 3, 2011)

Longer handle means you can get both hands on the handle and center the screw you putting in behind all your body weight, you gain balance as well. Combine all of these factors, and you almost double your torque output to the screw.


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## wormil (Nov 19, 2011)

It's all in your head. All other things being equal, a longer screwdriver provides no additional mechanical advantage. Also, you do not get additional energy from a longer tow strap as you can't get more energy out of a system than you put in.


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## hobby1 (Feb 10, 2012)

Torsion has a lot to do with it,
take a dowel, 1/4" dia. by 1" in length,put a pair of vice grips on both ends, and test how much pressure it takes to twist the dowel, to make it noticeable.

then take the same diameter dowel at, 48" long, and do the same, wich dowel twists easier.

Try it with a metal bar it still works the same.


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## patcollins (Jul 22, 2010)

If any of you have the strength to actually twist a screwdriver shaft enough that this theory is the reason then you must have some serioius biceps. Now consider that two small protruding tabs are all that keep the usually plastic handle on the screwdriver from twisting on the screwdriver shaft.


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## patcollins (Jul 22, 2010)

*Then when the object starts to move you have the energy of the towing vehicle plus the energy that is stored in the strap. You twist the long screwdriver some for that advantage. Go gettum Mike!!*

Grandpa, If the energy is released *after* the object started to move (ie screw starts to turn) that defeats the purpose.

It is all ease of use and ergonomics.


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## Underdog (Oct 29, 2012)

Pat…

It's not that hard to twist the shaft on a screwdriver. I'm not a body builder by any stretch of the imagination, but I've twisted several more than I should have. (Of course it depends on the diameter of the shaft!)

We're used to thinking that steel is inelastic and unyeilding. But steel, contrary to popular perception, is quite elastic.


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## CharlieM1958 (Nov 7, 2006)

Pat, if you have a long skinny screwdriver, it's very easy to prove it to yourself. Put it on a screw or bolt head that has been tightened as tightly as possible. Watch the screw slot very carefully while attempting to tighten it some more. You will feel yourself start turning the handle, but the screw head will not move. The effect is less noticeable with a really thick screwdriver because the flex is not as pronounced, but it's still there.


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## Underdog (Oct 29, 2012)

I think it's all about the point of connection to the lever arm.

With the stubby handles, you can't make a proper connection (your hand) to the lever (your arm). I can only wrap a couple of fingers around it instead of my whole hand.

It's kinda like using a sloppy crescent wrench on a rounded off bolt head.


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## CharlieM1958 (Nov 7, 2006)

"*Grandpa, If the energy is released after the object started to move (ie screw starts to turn) that defeats the purpose.*"

I agree with you on this point, Pat, which is why I said I thought Mike was "sort of" on the right track.

I say the twisting of the shaft, combined with the friction of the downward force you're putting on the screwdriver, allows that potential energy to be stored. Then, as you increase the force of your hand, those two sources of energy work together to begin the movement of the screw.


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## CharlieM1958 (Nov 7, 2006)

Dan (the original poster) is a retired teacher. I suspect he *knows* the real answer and is just toying with us.


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## patcollins (Jul 22, 2010)

Not saying that it isnt hard to twist a screw driver, im saying that the amount that it can be twisted stores very little energy.

Think about this, this behavior is non existant using nut drivers, torx screws, square drive, or anything that doesn't need a downward force to keep the driver on the screw.


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## CharlieM1958 (Nov 7, 2006)

Any further argument by me at this point would be pure BS, because the bottom line is… I just don't know.

It does surprise me, though, that I poked around on Google and could not really find anything more than speculation on the subject. You would think some PhD engineering or physics geek would have done the definitive study on this by now.


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## craftsman on the lake (Dec 27, 2008)

Dan (the original poster) is a retired teacher. I suspect he knows the real answer and is just toying with us. 

-Charlie M. "Woodworking - patience = firewood"

Retired science teacher actually, but that doesn't mean that I know.


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## 280305 (Sep 28, 2008)

On the user's part, wielding that Leviathan-like shaft might provide the rush of internal chemicals required to act as a Super Man. On the diminutive screw's part, it may just be frightened into easy submission.


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## Knothead62 (Apr 17, 2010)

Vise grips on the shaft plus putting weight on the grip do the trick every time.


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## Grandpa (Jan 28, 2011)

No doubt the longer handle makes a difference but I have some screw drivers that have identical handles and tips with different length shafts. Want to test this go buy some of those and see how it works for you. I never meant to imply that the tow strap was EXACTLY the same as the screw driver but the theory is the same. Anyone here ever heard of a flywheel?


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## patcollins (Jul 22, 2010)

This is one of those questions that can have multiple answers and they are situational.

Imagine the floor board in your house, you had screwed a 3 inch #8 wood screw into the floor boards and into one of your joists. The threads pull the screw into the wood so the force the wood exerts on the screw is on the top of the threads. Pushing down on the screw will releave some of this force, the force from friction is proportional to the force perpendicular to the surface so reducing this force by x% means that the force required to turn the screw is reduced by x% so pushing down on the screw makes it turn easier. A long handled screw driver just could make it more comfortable to do this and thus you can push harder. This is one of the principals that an impact driver operates on, just in spurts.

Lets take the pushing down part out of this equation and use the screw driver from the side, a long handled shaft in ths case would provide no benefit.

A flywheel has a couple purposes, to store energy and to smooth out the force from things like internal combustion engines so the power delivery is smoother instead of just spurts of power during the ignition part of the cycle, the flywheel also provides inertia that allows the piston to keep moving on the upstroke of the cycle.

I also think ChuckV's explination has something to do with it too.


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## wormil (Nov 19, 2011)

Charlie, I believe the question has been answered it's just that most people don't like the answer.

The basic physics are you cannot get more energy out of a system than you put in whether it be tow straps, screwdrivers, or flywheels. Screwdrivers are poor springs and almost all energy you expend twisting the metal is lost, you actually lose torque (if you don't believe me, imagine the drive shaft on your car winding up when you hit the gas). And as others have said, torque is applied at right angles by definition so the only way to increase torque is by making the handle wider. So the question has been answered many times over… all other things being equal, a longer screwdriver does not apply additional torque. A person might prefer a longer screwdriver because it gives them better ergonomics but personally when I have a stubborn screw I go for a larger screwdriver.


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## StevenWoodward (Aug 14, 2020)

I think with a longer screwdriver you can put more of your body into the task - that is what gives the increased torque.


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## craftsman on the lake (Dec 27, 2008)

> I think with a longer screwdriver you can put more of your body into the task - that is what gives the increased torque.
> 
> - StevenWoodward


Hi there. I asked this question in 2013 and it's still getting mileage. By you answering it, it will probably be revived because some people who have 'watch' on will get notification.


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## gdaveg (Aug 1, 2020)

Given the same size handle diameter on both a short SD and a long one it may be that there is a better chance of the long shaft driver being a more true vertical.

The bit stays in the screw slot / Phillips slot etc better. Less slippage gives us woodworkers more confidence to apply the power to it.

JM2C.

Dave


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## tvrgeek (Nov 19, 2013)

Only advertising violates the laws of physics.
One suggestion is a slight misalignment that keeps the tip still gripping is actually a longer lever with a longer handle. If you were perfectly aligned, it has to be the same other than your ergonomics.


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## Ocelot (Mar 6, 2011)

If your elbow is more bent, you can exert more torque. If you try to bend your arm like that with a shorty, you can't see the screw because it is too close to your body.

.. something like that.


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## Gadabout55 (Mar 3, 2013)

All other things being equal, the degree of mechanical advantage depends on the diameter of the handle and the amount of engagement between the screwdriver tip and the screw slot. But all other things are rarely equal. Different length screwdrivers tend to have different sized handles and different sized tips.


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## donwilwol (May 16, 2011)

I believe the length of the screwdriver has no bearing on the turning power, other than the added ability to add downward pressure.

I'll even bet the reverse is true. The short screwdriver has less surface to give, so it will give less.

All assuming the exact same downward pressure and direction of pressure is applied.


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## Finn (May 26, 2010)

> .......
> If the longer shafted screwdriver works better, it is because the rotational force is closer to your body, where you can really put the torque to it.
> 
> No laws of physics have been broke. Now y all move along, nothing more to see here.
> ...


My thoughts exactly!


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## tvrgeek (Nov 19, 2013)

Draw yourself a picture. Make the screw driver tilt just a degree or two. Look at the relative additional virtual diameter you are applying force to. Compare short to long handle.

But, ergonomics is probably most of it.


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## Gadabout55 (Mar 3, 2013)

> Draw yourself a picture. Make the screw driver tilt just a degree or two. Look at the relative additional virtual diameter you are applying force to. Compare short to long handle.
> 
> But, ergonomics is probably most of it.
> 
> - tvrgeek


I almost bought in to this, but no, you're still applying torque around an axis that is the screwdriver shaft. If anything, you are reducing the contact area with the screw slot slightly if you tilt the screwdriver.


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## spitfirepete (Feb 10, 2019)

with a longer shaft you can put more torque on screw. BUT only if the shaft is leaned slightly off plumb with the screw length. This has the same effect as increasing the the handle size….a little offset over a longer shaft will act as if it is increasing the handle diameter as you are rotating it in a larger area than if it was directly in line with the centerline of the screw .


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## Tony1212 (Aug 26, 2013)

> with a longer shaft you can put more torque on screw. BUT only if the shaft is leaned slightly off plumb with the screw length. This has the same effect as increasing the the handle size….a little offset over a longer shaft will act as if it is increasing the handle diameter as you are rotating it in a larger area than if it was directly in line with the centerline of the screw .
> 
> - spitfirepete


Even slightly moving off center doesn't do much to help. This video (starting around 0:43) shows that even with 30" of straight extensions on a torque wrench, the torque is essentially the same as having no extensions. Even if they allow the head of the wrench to drift off center.

At the end of the video, they put a U-joint on the wrench and show that by moving the wrench off center, it actually reduces the torque.


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