Hi again- Apparently there is no standard 'Grade' for Aircraft hardware such as
bolts and nuts, only Aircraft 'Quality'. Does anyone know of any 'Standards'
for this 'Quality'? The best that I can determine is that each manufacture of
Aircraft Quality Hardware have their own standards and are not made to any
'Industry' standards. I have found out that some manufactures will not even
give a PSI rating for their nuts and bolts, only stating that they are of
'Aircraft Quality'. Can anyone put more light on this?
There are strict standards... You see that 'aircraft quality' BS
statement thrown around all the time by marketers.
Only have a few seconds right now, but Google 'AN hardware' for a start.
Note that the vast majority of aircraft threaded fasteners are fine thread.
There are many special fasteners used in aircraft as well.
Fasteners will be spec'ed by the manufacturer for the purpose as far as
tensile strength, etc., using a specific set of spec's whether they be
military or internal for civilian aircraft. The "Quality" refers to the
QC pedigree that they meet the standard pedigree and have the paperwork
associated for whatever performance spec is pertinent; it doesn't mean
anything specific regarding what that performance spec to which it
adheres is; that's referred to but not the same thing.
It's like the "N-Stamp" for nuclear-qualified pieces-parts for reactors;
the actual spec's met are different depending on what the reqm't is, the
N-Stamp only assures that it was produced according to the protocol of
documentation and certification and record-keeping required which is far
beyond that of "ordinary" material which may, actually, be of precisely
the same actual functional spec.
For the most part, AN series bolts correspond to grade 5
every nut and bolt has been x-rayed for internal flaws.
Congress enacted theFastener Quality Act
(FQA) (15 U.S.C. 5401). Enacted in 1990,
the FQA has been subsequently amended
several times. However, the basic intent
remains the same, i.e., to ensure the qual
ity of fasteners and to prevent mismarked,
misrepresented, and counterfeit fasteners
from entering the commercial market.
When purchasing and installing standard parts, consider the
A Certificate of Conformity (C of C) should be provided by the producer
A standard part should carry a mark indicating the part has been
accordance with the specification requirements.
A part is no longer considered?standard? if it is used in a critical
imposes qualification or quality control requirements beyond the standard
To facilitate traceability, commingling like fasteners from different
lots is not
Section 21.303(b)(4) provides that acceptable government specifications are
limited to those published by the U.S. Government. Parts produced to a
standard may, however, be acceptable for in stallation on foreign
aircraft and products.
Installation of a standard part must bein accordance with the
requirements of part
43. Generally, a standard part may be replaced with an identical
however, substituting standard parts would require a demonstration of
acceptability in accordance with part 43.
Thanks - Oh yes, there can pages and pages of specs, but now I am finding out
why I was never able to see or obtain any of these specs. I would have to buy a
book or two to see these specs. I doubt if anyone is going to just print too
much information on this for free reading on the web. Of course I'll keep
looking but I don't have much hope for this. They will sell me an MS 39 bolt
but it is up to me to know what this is. I guess there is no Grade Number per
se` for an aircraft bolt - just 101 specs. Thanks again.
If they are labeling the bolts "aircraft quality" they are probably
not. Every bolt used in aircraft should have a spec. on it. There are
titanium bolts, SS bolts, huck bolts and every other type of fastener
and they all have a spec. on them. I believe that a lot of information
is listed in FAR 43:13 as to bolt specs.
Yes, check it out... go here and download a (free!) copy of AC 43.13-1B,
it's about 3/4 of the way down the page.
The full PDF is about 16.75 MB, but you'll have the option to download
it by individual chapter if you wish.
AC is FAA speak for 'Advisory Circular', they have thousands of them...
43 means it pertains to part 43 of the Federal Aviation Regulations
(FAR's) concerning Maintenance, Preventative Maintenance, Rebuilding and
Alterations. The rest is just the rest.
This is an interesting document, lots of very good information!
The section covering bolts proper begins at 7-34.
The FAA offers loads of other advisory circulars, handbooks and other
training materials, all free just for the download. I suggest one and
all take a look.
Hi guys - I am making progress, thanks...found a wealth of info on the AC43.B-1B
concerning identification of the hardware and some torque and dimension specs
but didn't find much on the actual specs other than that, but I sure haven't
read it all. I did come across what may be called a basic AN Bolt Designator
that may be interesting and necessary as a first step, at: Challengers
101.com/ANBolts. I did find a good site for some actual manufacturing specs on
AN Bolts but then lost it and couldn't find it again. And I did find a whole
lot a places that would like one to buy this information. I am finding it hard
to get into any of the Gov specific information. I will persevere, and thanks
again for everything.
Hi - Richard, You asked what am I trying to do. Well this can be a multi fold
answer. First of all, I am trying to learn. I use to own an airplane and I
would just buy a bolt without really know what I was buying. I didn't take the
time to determine what may be better - I just took other peoples word for it as
this is not too uncommon, right. For the last few years I have been drawing
hundreds of pictures of a different Gyrocotors and I thought maybe, just maybe,
I could find time to build a simple one. I use to look at the four fire-wall
engine mounting bolts of my plane and think, if I were doing this I sure would
have used heavier looking bolts. And as you may surmise, I should surely
understand the strength of a bolt to get anywhere with this. Even if I should
buy a 'kit' I know that I would be tempted to use a better bolt. And I thought
that I had better learn all I can on just what a better bolt may be. And then I
am always making things out of surplus Mil-spec bolts as stock, mostly of
stainless on my lathe, and again, it would be better to learn more about what I
may be using. I am retired now and I find myself trying to learn the things
that I didn't have the time to do before. That about covers 'what I am trying to
do' Richard...thanks for your curiosity.
You can make a quick guesstimate of tensile strength from 100,000 PSI
times the area of the thread root or the tap drill. Shear strength is
about half of that, for the shank or thread root, whichever applies.
For better numbers:
Ksi = KiloPSI.
On 2/6/2014 10:18 AM, Bob Lowe wrote:
I use to look at the four fire-wall engine mounting bolts of
Look, I have to say something that could be taken negatively, but I have
to say it. So, in the interest of safety and education consider this...
Until you can calculate the loads imposed on a fastener, _don't_ make it
stronger. In fact, don't make any changes at all.
Two reasons off the top of my head...
One: consider the structure that the bolt penetrates. A Larger bolt
means a larger hole too. Sometimes that will be ok - but sometimes the
edge margin could be critical and enlarging the boat could weaker the
attach point. In trying to make the structure stronger you could
easily make it weaker!
Two: sometimes structures are designed to fail in a particular manner.
Making a connection stronger in the wrong place could defeat that
strategy and cause a much worse failure to occur.
And three: A proven design doesn't need to be stronger. If anything
it needs to be lighter!
Just looking at a detail (like a 747 engine mount?) one often wonders
how the engine can possibly stay on the wing. But it does, quite well.
It's all in the numbers.
And using a grade 8 ot L99 bolt in place of the specified AN bolt MAY
also cause a failure. Better bolt? By spec, perhaps. In use? Perhaps
not. A grade 8 bolt MAY fail from vibration fatigue where the
"inferior spec" AN would not harden and crack.
Re engine mount bolts. I once had the job of removing the forward
engine mount bolt on an engine on an Air force Boeing 707. The A.F.
was trying some sort of iffy maneuver and the thing stopped flying
about 50 ft above the runway. After the Crash Truck had inspected
things and they taxied in the first inspection showed no ill effects
and everyone was quite impressed. The next morning one of the
maintenance troops commented that the cowling didn't seem to fit quite
right and after uncowling the engine and dragging up stands and much
peeping and peering it was discovered that the engine mount bolts were
bent and the engine was slightly out of line.
Apparently the Boeing engine mount designers DO know what they are
The final decision, by the Depot, was to remove the engine and then
gauge the engine mount brackets in the pylon, measure bolt holes for
elongation and do die checks of everything, which was where I came in
as the front bolt was bent too badly to simply drive out so the
Machine Shop was called for a solution.
After we got the bolt out without any damage to the supporting
structure they fiddled around for some time measuring, checking,
looking and reporting everything back to Boeing and finally about a
month later they hung a new engine and test flew it.
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