Help with Selecting the Correct 3/8"-16 Locking Nuts

Use a hammer and chisel to upset the thread next to the bolt. This can be done sufficiently to hold the nut against vibration while leaving it capable of removal with a wrench.

Thank you

I will submit one to their engineers and see what they say?

FASTENAL company has all-metal-stainless-steel locking nuts with high prevailing torque. No pins required. Shaped like a castle nut, but slots are narrower and ends bent toward the center. The nylon in Nylok nuts "cold flows" lowering holding torque.

A little more information would be helpful, like what kind of equipment/machine these nuts and bolts are used on? You mentioned that they subjected to vibration. What is the severity and duration is the vibrations? and are the bolt subject to any rotation?

Depending on the severity of the vibrations, a mechanical lock maybe your only option. Have you tried using a jamb nut?

Yes, We have tried several combinations of locking nuts and the only one that has a 0% failure rate is the slotted nut with a cotter pin. I did find some shorter cotter pins that may help with the install time. I would like to find a solution that we can just install with a wrench and be done with it.

As for the vibration? That is the $64,000 question. We fabricate a fall arrest system and this bolt holds the top post cap in place which is where the body harness lanyard attaches to. They are modular and man portable and install in their base plate with 2 quick release pins. We do not specify where these are installed and the units that we were having trouble with are mounted on a "MACHINE" and the only information that the company will give us due to non disclosure agreements and other "TOP SECRET" mumbo-jumbo is that it vibrates enough to vibrate off a NYLOK nut and the associated bolt out of its hole. So you see we are in the dark about the extent of vibration that is transferred from the "machine" to the fall arrest system.

Maybe they work on one of these?

You don't need to find shorter cotter pins, they're made of mild steel, you can easily cut them down with the right pair of pliers.

That is what we have been doing. In the first picture I posted, you can see that I show the cotter pin in its original length and one I cut down. However, when you cut the pin, you lose the offset length of the pin and must wrestle with the split end to try to open it up so it can be peened down. Here is a picture of the bolt at its nutted end. The aluminum round that the bolt is inserted into fits inside of shock arresting device. I'm not going to go into the engineering of this part because we fabricate these for someone else. We work with their engineers to find solutions for the problems / issues that arise with the installation and use of these devices.

The cotter pin must be configured this way to clear the harness attachment parts (not shown).

So far its looking like the most economical way that is going to achieve a 0% failure rate is the slotted nut and a cotter pin. I think that purchasing shorter cotter pins will definitely assist in the time reduction. Even a few minutes per part is a significant savings. and there is also the fact that sometimes while trying to peen the cotter pin, the installer "misses" the cotter pin and damages the powder coating on the finished exterior of the part and then the entire assembly is set off to the side, disassembled and the part is scrapped until it can go back to powder coat to be stripped and re-coated. A small mistake like this at the end of assembly is able to negate any profit we may have made and now we break even or go in the RED to get the client their parts. So you see, even an experienced operator can make a mistake and cause this to lose it's profit margin.

According to your last picture you do NOT need a thread since you do not tighten a part, so that you do not need a nut if you do not need a thread.

I would suggest to use a washer and a snap ring wit a correctly profiled grove in order to reduce the stress concentration. It is simple, easy to assemble and easy to disassemble it is insensitive to vibrations since you will never get such amplitudes to take the snap ring from its grove. If you need a limited axial gap (along the part to day threaded you can use one or several washers as a stack.

Your problem is the thread and if you do not need it you can avoid the problems by taking it off.

Sorry,

Actually the bolt and nut do tighten on the device, however we just shipped out our last unit and I didn't have one to take a picture of. The non threaded option may still work though. I will explore this option too.

Thanks

In fact the only reason to tighten is to maintain the "bolt" in place, your picture shows that the bolt is only a stop to axial movement of the ring with respect to the central piece.

If you use a straight bar - in fact a pin- it fulfills the function so that you have a straight steel with at each end a grove for a snap ring and between the snap ring and the ring a washer or more if needed.

Cutting a tread which ever method you use is more expensive than 2 groves. The solution keeps the axial position EXACTLY as your actual bolt and is NO sensitive to vibrations.

If you are afraid that radial movements could overload the snap ring then let between washer and ring a gap > than the gap between ring and central piece so that the contact will always be internal.

It really would save a lot of useless conjecture on the subject if the correct information was forthcoming from the first post instead of being fed to us like a weekly serial.

I too took that later picture to indicate that there was no tightening on the piece, and mentioned so in that post, hence my suggestion of the Clevis pin, which got no response at that time to tell us why that would not work.

I would have loved to have given you a full picture of the entire device but due to non-disclosure agreements along with other issues with some kind of secrecy on our customers end and that's why I cannot give you the entire picture. I'm sure you can understand my position I'm trying to get all the information I can't legally without betraying my customers trust

Why not a simple plate in the form of a tab washer ?

This picture prompted me to see if could do this more neatly. Here is my process;

Fit long pin and lightly tap head into the nut. Hint; ensure hole is up from base of castellation slot.

Bend longer leg over part way and snip off;

Tap down and then snip off excess of shorter leg;

This resulted in an overall dimension that was 1 mm larger than the across corners dimension. Will this work for you? Can you do this with your assembly?

I noticed that your split pin has a poorly formed head and you said that it was 3mm. The nut i have has a 3/32 slot and this makes for a neater finish. The bolt and nut are 3/8 24.

Hope this helps you.

Jim

Due to the legal liability and risk factor I would stick with the castle nuts and cotter pins.

In any process that affects personnel safety, quality must always trump speed of manufacture.

What happens when you try a jam nut? Does it perform better than the nylok?

A jam nut, unless somehow physically retained on the bolt will just vibrate off.

How about one of these backed up with a jam nut, the best of three worlds...

http://prolineracing.com/images/products/6100-00.jpg

I like that color of Blue, but those look basically a souped up Lynok®nut. If this harness mount is subject to enough vibrations for a nylon lock nut to come loose, I don't think these work either. And the cleats on the nuts will still vibrate loose, taking base material with it. Nylok's® shouldn't be used on bolts that are subjected to vibration or rotation or heat.

Some of the jet engines I deal with use 3 crimp nuts for assembling the hot sections, not a lot of vibrations and rotation, but you still can't afford failure.

And a lot of radial round engines I've worked on used stamped sheet metal "pal nut®" as lock nuts for locking the valve adjustment screw. They are subjected a lot of vibrations and another one you can't afford to have fail.

Not knowing the application, I would say what your doing is the best way to positively lock the bolt and nut. All others will come loose. Unless you could safety wire tie this but that adds more labor.

Fixit

Macgyver check out Anco locking nuts. These should work for you.

I checked out Anco nuts and found Lok-Mor Inc. and found something that may work. The Key-Lok nut - http://www.lok-mor.com/products/key-loc.htm looks very promising. I have contacted them and requested samples of several of their nuts.

This is probably an expensive way of doing it but try drilling down the side of the bolt and nut along the thread. Tap this out with a small fine thread and screw a bolt into the hole with Loctite. Try the vibration test. If it vibrates out try using an opposite handed thread in the hole. would be interested in knowing if this worked. It should as it did for us once but I don't know the severity of your vibration.

When automotive engines are operated at high RPM in racing forums, the rocker arms would loosen up after a while. The answer was Poly-locks. This is just a name hung on a combination of a hardened deep nut, and a headless Allen bolt. To install, just run the deep nut down to the desired torque, then holding the nut, run the Allen down till it jams against the bolt. The size used on small block Chevys was 3/8" fine thread.

I have a few questions though. Have you examined the bolt and nut after the system loosens? Are the threads on the bolt distorted? Can you use Grade 8 fine thread?

I need more LSD. I can not find a picture of Polylocks that agrees with my memory.

This is the product I was referring to above.

http://pitstopusa.com/images/F14601953.jpg

You haven't said what you are fastening together. If it is a fairly soft material then a nut with a knurled or pinned underside may suit your purposes as the pins would embed in the material and prevent loosening.

I have included a couple of pics. of some that I use.

The problem with the castellated nut/split pin (cotter pin for you yanks) combination is that accurate positioning and torquing is limited by the hole location which can make prefabricating difficult.

Prevailing torque lock nuts such as the din 934/980 series that deform the thread upon tightening could be a solution.

Another possibility is an HFR nut.

You should be able to Google up a bit of info on the ones I have suggested.

Can drill 2 cotter pin holes at right angles. I haven't had a case where that didn't give an alignment within acceptable torque range.

Depending on your particular case could you tap a thread through the piece that sits under the nut. Doctor the bolt to take a thread on the protruding bit of the opposite handedness and slightly smaller than the threaded piece. After assembly torque a nut to it. Hopefully as it vibrates one thread loose it will tighten the other. On the other hand it could just be an expensive thought.

Use either an oversized bolt, .002-.003" greater dia. or a reduced dia. nut. For the bolt, use a die with the a radial adjusting slot with adjusting set screws on it so that it is slightly oversized. Use standard nuts on this in a jam nut configuration. Change the threaded diameter of the bolt until you have a very tight fit with the nuts. Then jam then so they lock. The combination of oversizing bolt and jam nuts will not come loose. This is a standard practice for what you are looking for.

If you prefer, use nuts that are heavy duty of the next size smaller and drill them out to the tap hole size of the next greater diameter. Example, use a heavy duty 7-16" nut and drill it out with a 27/64" drill bit (tap hole dia. for a 1/2-13) and use an undersized tap to make a slightly reduced dia. hex net. Put this on a standard 1/2-13 bolt and jam another nut to it. Again extremely tight fit. These are easier to make and are tight enough to avoid vibrations loosening them.

Usually easier to purchase oversized bolts but also easy to make the undersized nuts.

Good Luck, Old Salt

A castle nut with a hitch pin clip the exact right length might be the most efficient method.

How about slotted nut with spring dowel pin?

Not yet, i will be looking at this option.

thanks

Or, just a (or two) tack weld (micro TIC), should be positive and cost effective...

Rivet?

I'm going to suggest the TIG tack weld to our staff and do some testing!

We never thought of a rivet in the slotted nut / bolt instead of a cotter pin, has anyone ever done this?

For double safety you should also provide split type lock washers. These are spring type lock washers available everywhere.

To give you an answer it is compulsory to know what and how you tighten with it, is it only one fastener or do you use more in parallel for same assembly ?

Is it a part threaded on both ends or is it a bolt with a head ?

Is it used as a rotating shaft ?

If you answer those questions it is possible to give you a correct answer.

A nut or a bolt gets loose ONLY under transverse loads and only if their amplitude is such that a sliding over a threshold occurs. If the parts can rotate on the fastener shaft and are loaded with a torque > friction torque due to assembly of course nuts or bolts get loose.

As you see solution depends on problem and cannot be given as a generic suggestion.

We had similar problems with fastening bonding cables to rails. The passing of trains causes massive vibrations if there are uneven spots on wheels or the rails. Currently we use nord-lock washers with the stainless steel studs or bolts and so far so good. When applied with torque wrenches it does not seem to work loose. Interesting concept, it takes more torque to loosen than to fasten. The link to their website is www.nord-lock.com and the principle is probably explained there. Some training for the installers into the principles is probably required, as i came upon a case where the two washers were reversed, thereby negating the while principle!

It is a "hard" assembly for which nord-lock is one of the best solutions. It is not known if the case we discuss is as hard as yours so that the solution could not be optimal.

All the discussion shows the "cut and try" approach and in bolted joints this is quite risky as many examples from the practical life show it.

1. Re-read post #8.

They already have an acceptable fastener that is qualified/vetted/accepted/ in use with 0% failure rate, by their customer. There is no need to "cut and try" anything.

Thank you for the remark but I did not mean the Op only those who give solutions.

The OP wants a simpler solution I tried to gather enough info in order to give him a good recommendation.

All other know already which is the best I am not so clever so that I ask for more, you see that is the situation when one is mind limited (I mean me).

Your remarks are always technically valid and on topic.

They are always helpful to the forum and the OP.

Lyn, I agree with you. After all, tie rod ends are still secured this way. I was going to suggest using a roll pin BUT I have seen these crack in half (lengthwise) and then fall out. The OP has trouble getting the split pin, after installation, into the next part. The roll pin would solve this. If the next part could be modified to retain the broken roll pin at least it won't undo. Maybe? It sounds like the bolt doesn't tighten against anything so a redesign using an axle and/or hitch pin may be better.

Jim

I have to agree with you, and not knowing what the $64,000 question is, the castellated nut and split pin is probably the best solution for the OP.

If they can't torque the nut to spec's and maintain castellation height, there are laminated shim washers that can be used to obtain proper castellation height at specific torque values.

Just wonder what the OP's R&D dept. has to say about all of this, they surely would have a lot more insight into this?

I would try a tab washer/plate device.

The tab folds against the nut and the tail folds against the workpiece.

Tab washer seems a simple good idea.

They can also be located by a key-like slot in the bolt/stud.

Do a Southern hill- billy ship yard fix--Tighten the nut, and then use a center punch, as a drift-pin, to expand the outer exposed bolt, using just enough force to jamb the nut. Works great, easily set up for mass production using a vertical ram, set to a precise amount of force necessary, but not too much as to distort the piece. Since it is probably unlikely that you would re-use the assembly, if disassembled, a one time shot should work..You might set one up in a vise and try it..Thanks for the problem!!

Not to speak for Brian but, it is my belief the equipment in question is life critical.

If I were going to climb into a harness and go over the side of a 20 story building with nothing but a harness, rope and a roof anchor between me and the ground, I'd much rather see a castellated nut and cotter pin holding me up than an unknown, unquantified, unqualified center punch mark on the threaded fastener my life depended on.

I strap myself into am strapped into race cars that go really fast. I would not climb into one that had a, "Southern hill- billy ship yard fix" holding me in the seat.

There was a time I would have......................................

I was of the understanding it (bolt) was attached to a "machine" that was attached to a fall arrest system. I can see a machine having enough repetitive vibration to work a fastener loose, but for the "Top Secret" fall arrest system, not so much, or they have a real problem…It must be related to a release and retrieval system…I know the punch system, previously ,mentioned can be and is used a lot, and with machining, a hole can be drilled and tapped into the end of the bolt , with an tapered expansion screw inserted and tightened as calc'd. This process kept the head on my old framing hammer for 35 years, and hundreds of thousands of nails without "vibrating" off…. Only a thought...

Putting myself into the seat of the purchaser, where I have been before, and knowing the legal, ethical and moral obligations I have to the ultimate user, I'll go with the 100% known effective configuration every time.

Not saying your method won't work 99% of the time.

Lyn--I totally agree with your viewpoint, just throwing out another viewpoint. As a former racer, you know what bailing wire and duct tape has done for a lot of poor, dirt racers . Best friend did it for years--Threw a Subaru boxer into a Fiat station wagon, and turned it into a dirt track, rear engine terror. He called it the "Subwat"…You racers crack me up (And sometimes , yourselves…) Personally like the Sprint cars, 900 HP pushing 1400 lbs of car….

Lyn,

I really enjoy your comments

I strap myself into am strapped into race cars that go really fast. I would not climb into one that had a, "Southern hill- billy ship yard fix" holding me in the seat.

There was a time I would have......................................

ME TOO!!!

I understand there is no disrespect, just a bit of good natured ribbing between people that have seen a lot of different mechanisms in their life.

I came up with this years ago. Never took it any further but I think with some refinements it would work. The worm screw has a left turning thread so it will resist vibration which the nut is subjected to.

Ky.

We seem to have lost Mr. O. MacGyver. There have been plenty of good workable solutions for his dilemma. If he wants assurance of fail-proof bolting, welding the nut to the bolt will solve the issue permanently. As long as the weld is quality, it becomes stronger than the bolt. If it is disassembled in the field, the bolt-nut combination will be destroyed, relieving the OP of liability. Welding is easier than the drilling of the bolt and hand installing the cotter pin. The next move seems to be in the OP's hands.

Sorry about that, My body decided it was time for a major weekend of rest and relaxation. Sometimes it's nice to just be a lump on the couch and shut off the computer.

Everyone,

Thank you for leading me in the direction of the watering hole, now it's time to drink from that pool of knowledge and move on. I have several fasteners I need to test. I will post the results of those tests soon. You all took the time to research and contribute in this matter and I feel as though I have a responsibility to follow up and give back to the community that has given so freely to me.

I have enjoyed the discussion immensely and look forward to posting and replying in the future.

Bryan

Looking at your recent lot of pics. it appears that the nut is not actually tightening onto the piece but is merely acting as a retainer for the bolt.

If that is correct, and tampering is not a problem, then have you considered not using a bolt but going for a clevis pin and over centre retainer somewhat akin to this:-

Or maybe this

With this

There are also retainers that have a spring loaded ball in the pointy end that would be neater than the over centre arrangement if that is critical.

As promised, Here are the results of the fasteners I have available:

• NYLOK nut - FAILED - due to vibration
• Standard nut with RED Loctite - FAILED - Their engineers did not like this option.
• Standard nut TIG weld tack - This process may impart too much heat to the powder coating finish and discolor it. We will explore this one further!
• Slotted nut with long cotter pin - cut the cotter pin to the shorter length and install. Difficulties - Cotter pin is difficult to install after being cut as it no longer has a staggered split end. Time consuming and possible damage to the coating.
• Slotted nut with solid 1/8" aluminum round - Cut 1/8" aluminum to 5/8" long and peen into the slotted nut. Difficulties - Possible damage to the coating as you have to hit it fairly hard to peen the aluminum pin enough.
• Slotted nut with short cotter pin - Since the cotter pin still has the staggered end we can grasp it easier and has reduced the install time in half!

• As of today, the best solution is the shorter cotter pin (1/2") with the factory staggered end. If I find a better solution, I will update the posting!

Thank you all,

Bryan

I commend your decision.

I think your customer will be satisfied that you have chosen the absolute safest and most positive safety device available.

I have always believed that giving the customer what they want, not what you want them to have, will result in a satisfied, repeat customer.

All through my working life I have dealt with many different people in many different situations. I learned from these encounters sometimes the hard way. I learned from some old machinists that the knowledge you have in your head is only good if you share it. I have followed that philosophy my entire life. I enjoy giving back to the community. If there is someone that wants to learn, I'm willing to impart onto them whatever I possibly can. ������������

Glad to see you are back with us. If I understand your picture, the nut is just jammed against the last thread of the bolt, not compressing the aluminum disc at all. If all that the nut does is just float in the assembly, I would suggest that you go to 3/8 X 24 thread. The above rocker arm adjusting nut is readily available, and sufficient to hold a rocker arm to an adjustment of thousandths of an inch for a duration of 600 miles at engine speeds over 8,000 RPM. Installation is easy. Tighten as needed, then hold the outer hex with a wrench, and use an Allen wrench to jam the internal set-screw against the bolt. Have you looked at this system before?

In post number 42 had you read the entire post you would've seen that I explained why the bolt was not tightened down on the aluminum there are just certain parts of this device I cannot take pictures up