Thick Thin Nut

Thin on the inside, thick on the outside.

I'm not sure there is a "standard." You can always try both ways and see which works best....

I agree with ozzb for the same reasons.

The thin nut needs a special thin wrench if it is on the inside and the tension must be adjusted. Sometimes the inner nut must be held against rotation while the outer nut is turned against it, otherwise both may turn.

You're right. It's in the texts, it's the way I was taught and 'standard practice' if not in a national standard somewhere, for road signs, traffic lights, across the railways, bridges, towers ....

I GA'd your first one

Logic is same however any one has seen this ?

_{BTW: I remember to have use this link in an earlier thread on same subject}

AP#1: I kind of like the explanation in your reference. The rest are a bit weak for me.

But I remain a skeptic. There is some recent fastener research that suppports the idea that loads on individual threads vary with their proximity to the loaded joint. There are also issues related to elastic deformation in the clamped members and the effect of vibrations.

Further your reference raises the issue of the effect of stretch in a long bolt shank. So to me a good answer to whf511's question must address the issue of the joint design, which is unknown at this point.......... Ed Weldon

I too am not entirely convinced especially at the 25-50% ratio.

As you said there is a thread load distribution, usually the first two-three threads take about if I remember 70-75% of the total load.

Now I would go for the process we normally follow.

Do the tightening of the thin nut at 50% say the stretch is 1mm and snug tight the nut. The upper (say away from the joint) flank of bolt will be in contact with the towards joint flank of the nut.

(If you now loosen the hydraulic tensioner the 50% of the required tension ie retained)

Now tighten the tensioner to full value (say now extension is another 1 mm - in the linear zone the fasteners work in it would be almost equal)

Now Snug tight the thick nut.

Note now the tension has created a gap between the thin nut bottom surface and the joint surface (which is 1mm - the thread clearance but definitely not zero and that too considering the fact that the thin nuts are usually higher precision nuts)

Though you now tighten the top nut (flush to the thin nut), as you release the pressure the bolt goes back all the way and the final retained pressure would be just above the 50% initial + the load corresponding to the thread clearance (which would add here) and a bit due to the deformation etc. But would be too far off from the 100%

Instead of the torques if you look from the elongation angle (and this is the actual tightening method) the picture differs.

Despite the link, hence I am more skeptic than you.

BTW - in most of our equipments we use double not, it is never thin and thick, it is usually both thick and the first one tensioned to almost maximum (say 90% or so the values are provided but it is usually not as low as 25-50%) and the second to 100%.

Thanks for the post, but after watching the videos and the hamfisted operator, it put me off ever even thinking of using that company completely.....

I wrote this on that website:-

The video demonstrations of thick and thin nut positioning are so flawed and badly carried out that anyone could set up the demo for any result they wished.

Firstly a torque wrench is needed to both lock down the first and the second nuts to preset agreed torque values.

Secondly, the use of an open ended wrench in the first video, and also at least once in the second, shows that whoever carried out the test does not know or understand the proper usage of ring and open ended wrenches.

If I carried out the test in a controlled and repeatable manner, I would not be surprised if the results were the opposite of yours.

Any Engineer worth his salt, who has been properly educated will go to another company before buying anything from yours after such an obviously poorly understood demonstration.

My advice is either do it properly, of leave it alone and remove the videos completely.....

I don't have a particular opinion on which nut first, but the test procedures they used were simply not accurate enough for me personally!

You have some good points there. In fact, we can only assume that the sockets shown were indeed used with a torque wrench. The slow motion of tightening would imply the use of a torque wrench, but the video should have zoomed out to show the torque wrench, and zoomed in on the wrench to show the torque values used.

The graph shown was not clear either. The vertical axis was labeled "Bolt Preload" (or something close to that). I presume the label should have been "Bolt Tension". If they indeed measured the bolt tension during the tests, They should have shown whatever device measured that in the video as well. Such a graph should be produced as a result of at least tens of tests, if not hundreds, but there was no indication of such...

In the first video, the failure appeared to be due to failure of the plated coating on the nut and/or washer, having nothing to do with the threads!

The more I think about this, the less convinced I am of the 'correctness' of any of these sources. There are so many variables. There might conceivably be a different best way for short bolts than for long bolts that have significant spring...

Yes.. I turned the sound right up to listen for the "click" of a torque wrench... grunts, passing wind..but no "click"!

Andy,

I too, watched these videos in amazement.

I learned nothing from them, no Torque wrenches, no proper calibration/ measurement of anything.

Why did they bother to make those videos?

Sleepy

Thanks for proving that I am not the only one amazed at the lack of quality shown in the videos.

I even posted on their website to them expressing my horror at the sight of such ineptness.....obviously it had no effect.

Try posting to them as well, maybe they will believe when more of us mention it!!!!

just seen the videos, Hogwash!

Who puts nuts on bolts that would be used on a vibrating unit WITHOUT spring washers?

Watching the first vid.. the nuts were NOT tighten down sufficiently!

I could not agree more......that is a company to avoid at all costs......

I think there is a general misconception (shared by even design personnel) about efficacy of spring washers.

When a fastement is tightened, the flanks are in full contact (or even a bit deformed) and the surface pressure on the thread flanks as well as the head (to the joint face) and the associated frictions keeps it from loosening (even under vibration)

The additional spring washer just keeps the pressure on the flanks to maintain the flank friction even when the fastener has loosened.

But does it? The spring constant of the spring washer is negligible (foa any size of fastener) compared to the preload of the fastener. So once loosened even a tiny bit, the surface pressure goes down manyfolds (making it easier to unfasten)

Additionally the hardened spring washer and the hardened bolt avoids bite (that the fastener head usually has on the joint material, usually softer). This reduces the friction too and makes it even easier to unfasten.

There are several technical papers on this (and if I remember there was an earlier thread too on this aspect where this paper was referred to). _{It is put in memory so I have removed the link from RAM. It would take a bit to search the paper out.}

In my experience, hardened spring washers usually cut into the nut or screw head somewhat, and cut significantly into the part being fastened. These cuts form ridges that significantly reduce the tendency to loosen, and remove significant metal from the part when the nut or screw is forcibly removed.

I don't believe I was ever taught either way, but I have always assumed the thick nut took the load and the thin nut was to prevent loosening of the thick one.

I hereby stand more educated!

Thanks!

And here, for a picture.

Where?????

Oops, I thought I inserted the link.

From the Engineers Campanion...
Jam nuts. These nuts are normally "jammed" together as shown in Figure 7, although the "experts" cannot agree on which nut should be on the bottom. However, this type of assembly is too unpredictable to be reliable. If the inner nut is torqued more tightly than the outer nut, the inner nut will yield before the outer nut can pick up its full load. On the other hand, if the outer nut is tightened more than the inner nut, the inner nut unloads. Then the outer nut will yield before the inner nut can pick up its full load. It would be rare to get the correct amount of torque on each nut. A locknut is a much more practical choice than a regular nut and a jam nut. However, a jam nut can be used on a turnbuckle, where it does not carry any of the tension load.

I was taught that the thick nut does the work, because of the surface area of contact between threads of the bolt to that of the nut, and the torque is therefore applied to the thick nut and bolts more evenly, and the thin nut, locks the thick nut in place.

Working on a ship, and watching the engine fitters torque down the foot bolts they used a hydraulic machine to stretch the bolts, then tightened down the thick nuts, then once completed, the thin nuts were torqued down on top.

That's the way to do it I feel!

The shipwrights should know best!!!!

I (maybe wrongly according to some other people) always put the thick nut on first, torque it down, then add the thin one for locking.....Just as you posted......but I don't have the nice hydraulic tool you mentioned though!!

I never thought about this...as I usually just use two of the same size nuts! If it needs to stay put forever, then I just add a bit of weld!

That will do it!!!

I don't see that the perceived lacking in a comparison based video have much to do with it - nor videos in general as cheating is too easy.

The mechanics are explained quite clearly in AP1's link.

I don't think witnessing someone doing it wrong has any bearing either - many do because they just "assume".

I for one, did it wrong, prior to study. Hence, I remember this so clearly, because of raising with my lecturer, the "anti-intuitive" use of the 'thin nut' to torque down the job. Thus got the "bonus unexpurgated" version.

However I believe I have found the reason it is not in a Standard and a lead to why it is "standard practice". I reproduce below the question and response.

"A jam nut is just like a regular nut, but only half as thick. It is there to "jam" against the other structural nut to prevent the nut from turning (in cases where you cannot pretension the bolt, such as A307s). They are not mentioned in the RCSC Bolt Specification because they are non-structural. The positioning of the nut (under or on the hex nut) isn't significant.

Charles J. Carter, S.E., P.E.
American Institute of Steel Construction
Chicago, IL

Several readers have written to let us know that most references and manufacturers recommend that jam nuts be placed under the structural nut. This practice is supported by references and recommendations from the Industrial Fasteners Insititute (IFI).

We must clarify, however, that jam nuts are not needed for structural connections with ASTM A325 or A490 bolts and therefore are not covered in the RCSC Specification for Structural Joints Using ASTM A325 or A490 Bolts (2000), available for free downloading at www.boltcouncil.org. Jam nuts are of interest, however, with some ASTM A307 bolts where it is necessary to prevent nuts from backing off in vibratory or similar applications.

Keith A. Grubb, S.E., P.E.
Charles J. Carter, S.E., P.E.
Chicago, IL

Pertinent parts; "They are not mentioned in the RCSC Bolt Specification because they are non-structural."

"jam nuts be placed under the structural nut ... is supported by references and recommendations from the Industrial Fasteners Insititute (IFI)."

Another reference, from fastener people, perhaps easier to understand than the Text Book version.

Thanks Tornado never seen that explanation on which goes where. Even in practice I have never seen it done that way.

What I do question about it is that thread depth has always been at least the diameter of the bolt. Or the the forces under torque may distort the thread to much or fail. With a thin nut first wouldn't that be a problem.