I agree to stay with aircraft quality fasteners, but it is really a lot more critical that any OD threaded fastener be aircraft quality. The first thing to fail in a fatigue or simple stress situation will never be the nut. Recognize also that any flexing of a bolt (such as a slipping wood propeller attachment) will quickly induce a lot of fatigue damage at the root of the threads of that bolt.
From my industrial experience, a simple Grade 2 nut will fail a grade 8 bolt.
Wow! I wish you would have kept the bolt! I would have loved to examine it! I scrapped alot of wrecked aircraft and found alot of bent bolts but none broken.. Of course it was all aircraft grade. If you find another broken bolt I hope you will save and share it with us.
Thanks Chuck
I broke an AN-3 bolt on my Fly Baby a few years back. It was on the bracket that clamped the tailwheel spring to the aircraft. Looked at it under a microscope, and it appeared that a surface flaw (either manufacturing or a nick on installation) let it start corroding across the cross-section. Replaced it with an NAS bolt and haven't had a reoccurence.
Back in '92, a windstorm blew a bit cabinet down on the wing of the original Fly Baby. The landing wires on the right wing failed.. one cable snapped, and the turnbuckle on the parallel landing wire failed in tension. Beautiful example of overtension...you can see the necking-down of the broken turnbuckle end where it failed.
Ron Wanttaja
I hate waiting on that one little part too, so I purchased a homebuilders hardware kit from Aircraft Spruce. This gave me a good variety to trail fit things with. I have several bolts of various sizes that are scuffed or dinged... those pieces are used for fitting and are kept in the parts bin for that purpose only. I sat down a few days ago and ordered nearly 15 pounds of hardware, just because I want to have more than 5 or 6 of some of the more common lengths and sizes. It takes a little time to go through and consider what you want to keep on hand, but it is way better (and way cheaper) than ordering the same size 8 or 10 times during your build. If I end up with a handful of various sizes left over, ah well... we are literally talking about a few dollars (my order was for over 200 pieces and I spent around $50). I'll keep em for the next project.
Perhaps you already have a pretty good variety and you are just lacking that one size... I get that. It's frustrating. Fortunately for me, Aircraft Specialties Services is a block away.
I guess I'm just suggesting that it would be easier and cheaper in the long run to keep a larger stock on hand rather than order the same parts over and over, even if I do end up with a vaiety of leftovers... that is the approach I am taking. Parts keep... freight charges buy you nothing.
There is actually a great deal of difference between AN hardware and regular 'hardware store' nuts and bolts--even Grade 8. Their use cannot be recommended in aircraft--even experimental aircraft.
There is a great deal of engineering and science that goes into something as simple as an AN nut and bolt. The metals and their strengths are specified. The surface contact area and shape of the threads are specified. Dimensional tolerances are specified. In engineering applications, even the order and progression of faiure--bolt vs. nut vs. hole---are specified. Manufacturers of AN hardware agree to hold and maintain these specifications during manufacture.
By example, it is my understanding that a hardware store Grade 8 bolt is actually 'stronger' than a liked sized AN bolt. But stronger is not necessarily better. A grade 8 bolt will tend to fracture in failure while an AN bolt will deform and bend before complete failure. This deformation is a significant warning system for stresses upon structures and engineers will build their structures around these specifications.
And--to no surprise--there is a significant amount of bureaucracy involved with these items. AN standards are no longer maintained by the Department of Defense are are considered obsolete for new designs since the late 1990's. NAS, AS, MS specifications are now incoporated into new designs. AN hardware will be manufactured for a long time to come but one should verify that these newer specifications are approved for the applications intended. AN does not always equal NAS, AS or MS standards and are not interchangeable for like sized components. Do your homework because their are gaps in the engineering data and specifications.
Hardware is a fascinating but somewhat dry field of mechanical engineering. But it is more dynamic than one would think. New NAS products are introduced all the time and the SAE is actively devloping fastners for all types of applications. You could spend a lifetime trying to learn the dynamics of these products. For building and maintaining aircraft, however, it's best to stay for approved products for engineered applications.
Even some of the NAS standards are not staying around. NAS15xx series screws are being superceded by a C series number. It can get confusing when you order one part number and get something else in the delivery and don't know it's been superceded. Makes the inspectors go crazy til you can show the proper documentation.
The big difference between hardware & AN/MS bolts is the aircraft ones have the threads rolled AFTER heat treat, giving better fatigue resistance. Aircraft also have more unthreaded shank length options and certain premium series also have better shank diameter control.
Aircraft nuts however are just tapped like hardware ones.
Oh for the days after WWII, when you could go down to the war surplus store and buy a nail keg of floor sweepings (AN nuts, bolts and etcetera) for a couple of bucks. Then there were the years when Boeing Surplus sold them for $1/lb. Those days are gone forever.
If the correct sizes for your project are still available, I would opt for using certified hardware. The chances of getting a faulty part are much slimmer than with hardware-store fasteners. You can still get poor quality aircraft fasteners - I had to go through a bin of long bolts once to find eight which were threaded straight enough to fasten my horizontal stab on the fuselage.
Perhaps a trick which a good friend of ours used when building his RV-4 will work for you. Wherever possible, he assembled his plane with hardware store fasteners. He had spray-canned them all in a bright color. After he was finished with an assembly and just before closing it up where doing so might render the fasteners difficult to reach, he would determine the exact sizes he needed, purchase the aircraft hardware, and install them en masse. He may even have saved a couple of ounces of weight by using a minimum number of washers.
By concentrating his efforts on just installing bolt and nuts, he was able to align the heads, screw slots, bolt direction and other details to make a prize-winning airplane. When he finished, the only hardware left over was a lifetime supply yellow-painted imported nuts and bolts.
A larger question is where one is using hardware store nuts and bolts.
On my little Nieuport I put in some supports for the turtle deck stringers, which are just 1/4 inch tubing, to keep them from sagging when I go to cover it. The supports are just some 1/8" ply cut to fit and placed on top of the crossmembers of the fuselage underneath, and are held in place with some loop clamps, which are fastened to the ply using bog standard bolts and locking nuts.
Why? Because they're more than just a few cents cheaper!
It's completely non-structural and a non-issue should they fail. Indeed, if they would fail that would mean the entire fuselage has deformed - at which point the issue of whether or not the turtle deck stringers are liable to sag is the least of my concerns!
For anything load bearing or structural I'm using aircraft grade stuff, though.
The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.
If there are any FBO's with a maint. shop you might get the couple of pieces of hardware from them and just replace their stock when your order comes in, just do it in a timely manner and don't blow them off, you may need them again. Some times its hard for a shop to justfy making up a workorder for a few pices of hardware so replacing what you "barrowed" usually works for me, or taking them to lunch some time is good too, usually worth more than one shopping trip for pieces.
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