This should help:
Standard aircraft bolt, hex head. Made of high strength 8740 or 4037 alloy steel with 8740 being the most common. The length of an AN bolt is measured from under the head of the bolt to the end of the shank. The grip is the part of the bolt that is not threaded. The minimum tensile strength of an AN aircraft bolt is 125,000 PSI
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AN Bolts
Karl