<< > > > Robin wrote:
 > > >
 > > > Hello Paul,
 > >
 > > >     I hope this doesn't immediately sound like a dumb question, but how
 > can you find out exactly what the particular specifications for any given
 > "AN" part is?  For instance:  Metallurgist typically say there is just
about
 > no difference between an American made grade 8 bolt and an AN bolt.  Well,
 > that's fine and dandy and we all can see that relationship pretty well when
 > you're talking about common fasteners, but what happens when you begin to
 > talk about other products?  How can you really make a sound comparison?

snipped

Charlie Kuss wrote:

  At one time, I shared Robin's opinion regarding hardware.  There are considerable
differences between a commercial grade 8 bolt (stronger, relatively brittle) and a
common (not high strength) AN bolt. AN bolts are actually softer. They are designed
to fail "gracefully". This means that rather than cracking or snapping when over
loaded, they will stretch. A broken grade 5 commercial bolt (a closer comparison to
the most common AN bolts) and a stretched AN bolt are both junk. The difference is
that when the commercial hardware fails, it fails catastrophically. Part of your
aircraft may fall off. (I hate when that happens) The AN hardware gives you a chance
to get the craft back on the ground. Hopefully, you will find that it has failed
during your next preflight. Of course, this nice feature is totally useless IF you
don't do proper preflights and follow proper preventative maintenance procedures.

 As you progress from grade 5 up to grades 7 & 8, the commercial bolts are even more
likely to fail catastrophically, as they are even more brittle. Hi strength AN
hardware is much less likely to fail in this manner. In short, AN hardware provides
a certain "safety net". You ought to try reading FAA AC 41.13-1b  It is very
educational. I've learned a lot from it. As I learn more, I realize that I knew and
still know a lot less than I thought I did.

  I'm sure that there are areas of each ship where you can safely substitute
commercial hardware for AN hardware. Please be careful that you don't use commercial
hardware in flight critical areas. I don't want to read about anyone here in the
NTSB accident reports.
Charlie Kuss
RV-8A fuselage   (better to study on the ground, than be tested in the air)
Boca Raton, Fl.

 
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