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Identifying AN Bolts: Sizes and Nomenclature

Identifying AN Bolts: Sizes and Nomenclature
Ordering AN Bolts can be confusing because they are so different from SAE bolts. SAE bolts are identified by overall shank length, and they generally have much longer threads. AN bolts are called out by grip length, and they have shorter threads.

Grip refers to the unthreaded portion of the shank. This is the portion of the bolt that should bear against the inside of the hole. The threaded portion is not as strong as the shank in shear and does not present a good bearing surface for the parts being bolted together. Under vibration or movement, the threads can damage the hole.

Thread Length is constant for each bolt diameter. It is calculated to be enough for one AN960 flat washer under the head, a full-height AN365 or AN310 nut, and one AN960 flat washer under the nut. Grip lengths are in 1/8" increments. AN960 washers are 1/16" thick (1/32" thick for the L version). If your application falls between two grip lengths, you can add one or two more washers to a bolt with the next longer grip.

AN bolt nomenclature follows this format:

ANd(H) - g(A)

d is the bolt diameter (in sixteenths of an inch)

H indicates that the head is drilled for safety wire (no H indicates undrilled head)

g refers to the grip length*

A indicates that the shank is NOT drilled for a cotter pin (no A indicates drilled shank)


AN4-15A:  1/4-28 bolt, 1 3/16" grip, undrilled head, undrilled shank

AN6-20:  3/8-24 bolt, 1 7/16" grip, undrilled head, drilled shank

AN5H-27A:  5/16-24 bolt, 2 7/16" grip, drilled head, undrilled shank

* Note: A popular misconception is that the dash number gives the shank length in full inches plus eighths of an inch (-15 would mean 1 5/8" shank length). The numbering sequence seems to back this up -- the dash numbers skip right from -7 to -10 (i.e., -8, -9, -18, -19, etc. are not used). This would be convenient, but in reality it is not the case. Each dash number specifies a different length for different bolt diameters. You must refer to a size chart or AN bolt gauge to find the correct dash number.

The bolt grip length charts linked below are especially handy when replacing non-AN bolts. Measure the total thickness of the parts being bolted together (not including washers, nut, or female threads). Locate the bolt diameter and grip length (total thickness) in the table to find the required dash size.

pdf icon AN Bolt Grip Length Chart (Decimal)
pdf icon AN Bolt Grip Length Chart (Fractional)
Torque for dry, cadmium plated threads per FAA AC 43.13-1B
Bolt Size Thread size Full-Height Nuts
(AN365 or AN310)
Half-Height Nuts
(AN364 or MS21042)
AN3 / AN3H 10-32 1.5 to 2 lb-ft 1 lb-ft
AN4 / AN4H 1/4-28 4 to 6 lb-ft 2 to 3 lb-ft
AN5 / AN5H 5/16-24 8 to 12 lb-ft 5 to 7 lb-ft
AN6 / AN6H 3/8-24 13 to 16 lb-ft 8 to 10 lb-ft
AN7 / AN7H 7/16-20 37 to 42 lb-ft 23 to 25 lb-ft
AN8 / AN8H 1/2-20 40 to 57 lb-ft 25 to 34 lb-ft
AN Bolts
AN Bolt Identification Gauge
Printable AN Bolt Grip Length Chart (Decimal), PDF Format
Printable AN Bolt Grip Length Chart (Fractional), PDF Format

This article was first published on 7/23/2012.

It was most recently modified on 3/26/2015.