GRADE 8 BOLT
BY JOE NORRIS
I WAS IN A friend’s shop and was looking
for an AN bolt. While looking through the
bins a few bolts caught my eye. Closer
examination revealed that some Grade 8
bolts had gotten mixed in with the AN
bolts. This is easy to do since the finish on
a Grade 8 bolt is similar in appearance to
an AN bolt. But you don’t want to use a
Grade 8 bolt in place of an AN bolt! True,
Grade 8 bolts are stronger than AN bolts
in tensile strength, but that does not make
them better. There are other properties
that differentiate Grade 8 bolts from AN
bolts that may make them a poor choice
in aviation applications. You don’t want
to use a Grade 8 bolt in your aircraft
unless you are specifically directed to do
so by the designer or plans/kit vendor.
Fortunately, it’s pretty easy to see the
difference between a Grade 8 bolt and an
AN bolt. The first and most obvious difference is the length of the threads on the
shank of the bolt. For any given length, a
Grade 8 bolt will have considerably more
threads and less grip than an AN bolt. The
other difference is in the markings on the
head of the bolt. A Grade 8 bolt will have
six lines arranged radially, lined up with
the six points of the hex head. A standard
AN bolt will typically have either a cross
or an asterisk in the center of the head.
There may be other markings on the AN
bolt head as well, but the cross or asterisk
will be incorporated into those markings.
Next time you’re in your shop, take a
look in your AN bolt bins and make sure
there are no Grade 8 bolts mingling with
their AN cousins!
Far Left: Grade 8 bolt has radial lines
pointing to the corners of the hex head.
Left: AN bolt will generally have an “X”
somewhere on the head
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Note the similar color but much longer thread length of
the Grade 8 bolt (on the right in each pair) as compared
to the AN bolt.
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