Aircraft building tips, Bolts and Grip
Part two of our series continues with a description of bolt coding, screws and related hardware. As it is important to use the correct bolt (AN type) with the correct length we present a table for you to check if the correct bolt is used.
Bolts and grip details
AN bolts may be used for either tensile or shear load/applications. The material used is cadmium plated nickel alloy steel (Has no letter designation, head is marked with a cross or asterisk), corrosion resistant steel (C designation, head is marked with single dash) or Aluminum alloy, 2024-T3 (DD designation, head marked with two dashes).
The diameter is denoted by the number following AN. Thus AN3 means a bolt with 3/16 inch diameter. The number following the dash indicates the length in eighths (1/8) of an inch up to 7/8. If a bolt is longer than an inch the first digit is the number of inches and the second digit is the number of eighths. For example: AN3-12 is a bolt with 3/16 inch diameter and the length is 1 inch plus 2/8 or 1-1/4 inch long.
AN bolt description and coding
AN bolts are coded according to a certain standard. The coding of a hex head AN4-(H)10A (for example) bolt is as follows:
| AN | Army Navy Standard |
| 4 | Diameter in 1/16", thus this bolt is 4/16th of an inch in diameter |
| - | Steel, cadmium plated (C = Corrosion resisting steel, DD = Aluminum alloy) |
| (H) | Drilled head, leave off if no hole is required in the head |
| 10 | Length is 1 inch (see table below) |
| A | Cotter pin hole not required |
The AN bolt was originally designed to be used with a castle nut and cotter pin where the shank is drilled for the pin. If you wish to use a self locking nut the shank should not be drilled (A designation - AN5-7A). If the bolt is used in a blind closed hole the head should be drilled to safety the bolt (H designation).
And because a picture says more than the table above (or a 1000 words) I have included this layout below:
Recognizing the proper aircraft bolt can be somewhat difficult as they are coded with special symbols embossed on the head. The image to the right shows the possibilities:
Bolt Grip length
To determine the bolt grip length, deduct the figure below from the lengths show in the table hex head bolt length.
AN3 - 13/32, AN8 - 25/32, AN14 - 1-1/4
AN4 - 15/32, AN9 - 29/32, AN16 - 1-3/8
AN5 - 17/32, AN10 - 61/64, AN18 - 1-1/2
AN6 - 41/64, AN12 - 1-3/32, AN20 - 1-11/16
AN7 - 21/32
AN3-AN20 Hex Head Bolt Length
| Bolt | AN3 | AN4 | AN5 | AN6 | AN7 | AN8 | AN9 | AN10 |
| Dash nr | 10-32 | 1/4-28 | 5/16-24 | 3/8-24 | 7/16-20 | 1/2-20 | 9/16-18 | 5/8-18 |
| 3 | 15/32 | 15/32 | - | - | - | - | - | - |
| 4 | 17/32 | 17/32 | 19/32 | - | - | - | - | - |
| 5 | 21/32 | 21/32 | 23/32 | 45/64 | 23/32 | - | - | - |
| 6 | 25/32 | 25/32 | 27/32 | 53/64 | 27/32 | 27/32 | 31/32 | - |
| 7 | 29/32 | 29/32 | 31/32 | 61/64 | 31/32 | 31/32 | 1-1/32 | 1-1/64 |
| 10 | 1-1/32 | 1-1/32 | 1-3/32 | 1-5/64 | 1-3/32 | 1-3/32 | 1-5/32 | 1-9/64 |
| 11 | 1-5/32 | 1-5/32 | 1-7/32 | 1-13/64 | 1-7/32 | 1-7/32 | 1-9/32 | 1-17/64 |
| 12 | 1-9/32 | 1-9/32 | 1-11/32 | 1-21/64 | 1-11/32 | 1-11/32 | 1-13/32 | 1-25/64 |
| 13 | 1-13/32 | 1-13/32 | 1-15/32 | 1-29/64 | 1-15/32 | 1-15/32 | 1-17/32 | 1-33/64 |
| 14 | 1-17/32 | 1-17/32 | 1-19/32 | 1-37/64 | 1-19/32 | 1-19/32 | 1-21/32 | 1-41/64 |
| 15 | 1-21/32 | 1-21/32 | 1-23/32 | 1-45/64 | 1-23/32 | 1-23/32 | 1-25/32 | 1-49/64 |
| 16 | 1-25/32 | 1-25/32 | 1-27/32 | 1-53/64 | 1-27/32 | 1-27/32 | 1-29/32 | 1-57/64 |
| 17 | 1-29/32 | 1-29/32 | 1-31/32 | 1-61/64 | 1-31/32 | 1-31/32 | 2-1/32 | 2-1/64 |
| 20 | 2-1/32 | 2-1/32 | 2-3/32 | 2-5/64 | 2-3/32 | 2-3/32 | 2-5/32 | 2-9/64 |
For a more complete printable version click here.