EAA Sport Aviation - November 2010

GRADE 8 BOLT
IDENTIFICATION

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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