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AN - NAS - MS
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Bolt Measurements

Grade 8 Fasteners Flat Head Bolts Aricraft Bolts
(NAS, MS)
Aricraft Bolts (AN)

Printable Measuring / ID Guide

.PDF format

Hex, Socket Head, Button Head, 12 point Grade 8:

All hex head, socket head, button head and 12 point grade bolts are measured the same: Diameter, thread pitch, under head length. They are ordered the same : Diameter (1/4) - Thread pitch (20) x Under head length (1-1/2") or 1/4-20x1-1/2".

1/4-20 x 1-1/2"

1/4 = diameter
20 = thread pitch
1-1/2" = Length

Thread Pitch (threads per inch):

Diameter

Coarse (UNC)

Fine (UNF)

2 56 -
4 40 -
6 32 -
8 32 -
10 24 32
1/4 20 28
5/16 18 24
3/8 16 24
7/16 14 20
1/2 13 20

Flat Head Bolts / Screws:

Flat head cap screws are measured pretty much the same as hex head bolts, but the overall length is measured rather than the under head length. See the below illustration for measuring information. This system applies to NAS flathead fasteners as well, jus substitute the dash number for the length (1-1/2 length = -24: 24/16ths = 1-1/2) and diameter (1/4 = 4/16 = -4)

1/4-20 x 1-1/2"

1/4 = diameter
20 = thread pitch
1-1/2" = Length

Aircraft (NAS / MS) Bolts:

Aircraft bolts are measured and ordered differently than non-aircraft fasteners. Less emphasis is given to the length and more is placed on the grip length. Grip length is determined by the thickness of the material being clamped. Grip is measured from under the head to the start of the threads. Do not forget to add the washer thickness in determining the overall grip. Grip is measured in 1/16th inch increments.

All of the pertinent information about aircraft bolts are shown in their part number. All of their measurements (grip and diameter) are in 1/16th increments. They are ordered by style (see identification page), diameter and grip length. All aircraft fasteners are fine threaded. To determine the overall length, add the grip to the thread length (see table below). See above flathead measuring guide for flathead NAS / MS bolts.

NAS1304-28
NAS13
: Bolt series / style (see identification page)
04: Diameter in 1/16th's (4/16 = 1/4)
-28: Grip length in 1/6th's (28/16 = 1.75")
1304-28 = 1/4-28 thread, .425 thread length + 1.75" grip = 2.175" under head length
Thread Lengths:
Bolt Style
11XX 62XX 13XX 66XX 65X 67X 64XX 62X MS
21250-X
MS
2000X
Bolt Diameter
-3 (10-32) .276 .323 .338 .345 .276 .338 .323 - .420 -
-4 (1/4-28) .316 .370 .425 .425 .316 .425 .370 .485 .492 .475
-5 (5/16-24) .375 .438 .469 .469 .375 .469 .438 .572 .579 .537
-6 (3/8-24) .391 .454 .578 .578 .391 .578 .454 .619 .625 .662
-7 (7/16-20) .453 .528 .594 .694 .453 .594 .528 .694 .721 .787
-8 (1/2-20) .453 .528 .735 .735 .453 .753 .528 .741 .768 .787
x = Bolt Diameter
Aircraft (AN) Bolts:
AN bolts have little rhyme or reason to how they are measured. They are ordered by diameter (again, using the 1/16th dash #), but the grip / overall length has to be derived from the below chart.

AN6-15A
AN
: Bolt series / style (see identification page)
6: Diameter in 1/16th's (6/16 = 3/8)
-15: Grip length (see chart) - 1.060"
A: No hole in head or shank (most common)
AN6-15A = 3/8-24 thread size, 1.70" under head length (see chart)

AN Bolt Lengths

 


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