AN Locknuts vs Store bought locknuts.

[Allantat]

A question here for the A&P's on the forum. We know NOT to use store

bought bolts and have heard the arguments vs Grade 8 and AN Hardware

with AN winning all the time. However...does this hold true for locknuts?

We have been taught NOT to reuse them. Toss'em..... get another. I'm

currently assembling my rotorhead and had to disassemble meaning the lock

nut was relegated to the junk box. I do have several NEW AN LOCKNUTS

which I will use! I also had some new unused "store bought" locknuts of the

same size. So...is a "locknut a locknut" whether it's Cad plated or chromed?

Is there a difference?

The picture shows the AN locknut on the left with the 2 hardware store nuts

on the right.

[gyroplanes]

Hi Allan,

I feel comfortable answering this as I am both and A&P and DAR. There is no requirement to use FAA Spec hardware on experimental aircraft, so the call is your's to make.

I, personally, would feel a whole lot more comfortable using hardware store locknuts than bolts, especially in shear applications.

I would never use any hardware store fasteners in any critical application.

Now, the good news! There is no regulation or need to discard AN lock nuts after one useage. This "Old Wives Tale" probably dates back to the pre-nylon lock nuts of today. The rule of Thumb for lock nuts is that if a wrench is no longer needed to tighten them, they should be discarded. Also, the "chrome" plating you refer to is in all probability silver cadmium plating, it is also found on AN hardware from time to time.

The FAA has a chart of Prevailing torque minimums to use to establish if a nut has lost it's locking ability, unfortunately the chart begins at 7/16" and goes up. I guess the cost of the larger AN nuts demanded a proof positive way to determine their life.

I have been wrenching on aircraft for 30 years and have never seen a failure of a used lock nut. They are reused all of the time.

[dapartlow]

Thank you Allan & Tom, That was something I also wanted ask but felt DUMB to ask it.

[automan1223]

Tom,

I have personally had a few an 4 .....1/4" locknuts come off and go a missing in flight. They were reused, more than once, still had tension and were subjected to vibrations up near the rotor head to the forward supports. Thankfully the bolts were in shear and gravity somehow kept them in. My replacements were new bolts, High temp, high strength locktite and new nuts. I dont know if its just me but I have had too many Oh, my gosh's to ever feel comfortable with half assing it., Do it right, Check it, double check it and then once you think you are paranoid, tripple check it. When you are flying then the only thing on your mind is fuel consumption, birds and the bee's........

Even after my 40 hours has been flown off and several trouble free hours...... my aircraft is a labor of love that if I stop paying attention too will soon bring me back to the ground for some attention. My thoughts are if its enough to get your attention, why not fix it while you can give it your attention. "Fix it before it...fixes you".......

Jonathan Weis
Oriental NC

[donshoebridge]

I'm using the MS21042 all-metal lock nuts on my Hornet. These are the same nuts that I used in the USAF. I have never seen a nylock nut on an F-16 before, so I figured there was a reason for it. Also, there's less metal on the MS21042 nut, and therefore, it's lighter. And just as Tom stated, if you can thread them on and off with your fingers, replace them.

http://www.aircraftspruce.com/catalog/hapages/an363.php

[scott heger]

I just had a used "an" locknut loosen and depart on me last weekend off my lower prerotator...and where did it go ? Into the props of course, one small ding for the washer under the nut on one prop, one slightly larger ding on a second prop where the nut probably hit. I checked the installation manual, and it called out for a castle nut in this location, my fault. Would a new locknut have come off? Well it hadn't in 5 years and hunderds of hours of flying before; was it worth the damage/risk it caused? No way!!! Live and learn.


Scott heger, Laguna Niguel, Ca N86SH

[automan1223]

Scott, all.....

You have no idea how good locktite is if you use it correctly. The high temp & high strength stuff works great. In fact if you use it with clean parts, and the spray primer that usually no one buys, or uses the stuff works so well you will have one heck of a time taking what ever it is you put together with it. It will come apart without heat though, and you have to work fast with it. I have never been a total fan of small cotter keyed fasteners cause I have seen them fail right at the hole.

Jonathan

[FrankieJ]

Don by the look of things I think the nut you are using is what we refer to as a crush nut - that is when you tighten the nut it crushes down onto the thread and locks both nut and bolt together, mainly used in areas of high vibration and temps (nylon melts) best results wack on some 222 or 242 locktite. These crush nuts can be hard too get off and can only be used once

[donshoebridge]

Frankiej,

The inside diameter of the nut is oval shaped. As you run the nut onto the thread, the bolt reshapes the ID of the nut to round. When you remove the nut, is goes back to its original shape. The USAF never replaces these nuts after one use. The only time they would be replaced is if (like has been said in this thread) there's no bite left or the nut is damaged beyond "servicable". There is enough bite with the MS nuts that you do not need Loctite. After several uses, the MS nut still has more bite than a new nylock nuts does. What gives out first on the MS nut is the hex. After using the same MS nut over and over, I have rounded the flats off, but it still has plenty of bite on the bolt.

[Charles]

Hi fellaws...
I use stainless steel nylocks and washers all over my gyro and am sure rust will never take over.
As for strenght, I'm sure it will never break off. As for durability, as Tom said,
I will replace it when it easily unscrews by hand or more. I'm sure the nylon inside is the same as AN nylocks.
They cost a little more but my mind is quiet when I fly. I always check everything before flying.

I am wondering if stainless bolting would be acceptable in aviation. At the price these hardwares are at, it could be an alternative if threading would be
as required. Stainless steel has much more strenght than AN steel.

I know it could bring some chemical reactions with time but how long will it take to react? I put on grease before tightening the nylocks all the time.

Would appreciate some opinions...

Charles Gagne
Quebec city P.Q.
Canada

[donshoebridge]

One thing that I would worry about regarding stainless is the source. There are cases where cheap Chinese stainless comes into the US and is sold at hardware stores all the time. Some of it is soft and will gall-up on the threads and/or the threads will fail altogether. Just something to watch for.

[Doug Riley]

Where does the notion that stainless is stronger than AN steel come from? Stainless steels as fabricated are typically a little weaker than mild steels, which is to say they're in the 70,000 psi tensile department. AN steel is heat-treated to 125,000 PSI. A stainless bolt from a retail source with no particular specs is unlikely to meet AN strength specs for steel bolts... but the real point is that you just don't know.

Stainless reacts with aluminum in the presence of acidic or salty moisture (i.e. an electrolyte) to corrode the aluminum. This is a problem even on boats, where thick anodizing is applied to protect the aluminum. The aluminum turns to white powder, similar to the stuff that accumulates on the terminals of your car battery.

I've found the plating on hardware-store bolts, while supposedly cadmium, is so thin that the bolts rust within months of installation. The AN bolts' plating is either better done or thicker, as it holds up much better.

[Jazzenjohn]

I think many people associate Stainless steels difficulty to machine as evidence that it's stronger. It is difficult to machine, and it's tougher, but it isn't stronger.

[Robert G. Stark]

The AN hardware is tried and tested. The small savings you could get from hardware store stuff does not match up to the cost of failures.

[mikegrady]

Why do you guys not safety wire stuff? I raced karts and I safety wired everything that mattered except the wheel nuts. I would think vibration would be a concern with a vehicle of flight? Nylocks are fine for bodywork. I used little stainless bolts and nylocks all over my karts for corrosion resistance BUT not on stuff that matters......like engine, hub, wheel, steering, brake, or axle fasteners. Lose a steering end at 70 mph and you are going to get hurt. Lose something in the air and you can die. I was under the impression that everything in aircraft was wired but I am finding out that I was wrong.

Am I missing something......?

Thanks,
Mike Grady

[donshoebridge]

Why do you guys not safety wire stuff? I raced karts and I safety wired everything that mattered except the wheel nuts. I would think vibration would be a concern with a vehicle of flight? Nylocks are fine for bodywork. I used little stainless bolts and nylocks all over my karts for corrosion resistance BUT not on stuff that matters......like engine, hub, wheel, steering, brake, or axle fasteners. Lose a steering end at 70 mph and you are going to get hurt. Lose something in the air and you can die. I was under the impression that everything in aircraft was wired but I am finding out that I was wrong.

Mike,

We do safety wire wire on "...everything that ..." matters. There are a few areas that do not have self-locking hardware like the air cleaners, prop bolts, and others. Those are typically wired. I'm not a big fan of the Nylock nuts and that's why I'm using the MS lock nut. The MS nuts have better bite and are made for high vibration and high heat application because there isn't any nylon locking material used in them. Their all all metal. It's the same stuff we used on ejection seats and canopy assemblies on F-16's when I was in the USAF. The rule there was if it's not self-locking, then it get's wired.