Using and installing the correct hardware, bolts and nuts, in aircraft is imperative. Non aviation grade hardware just does not have the strenght or corrosion resistance suitable for application in our project. We would we playing with our lives and that of others by using these inferior bolts and nuts.
To be able to recognize the correct hardware we continue with a description of bolt coding, screws and related fasteners. As it is important to use the perfect bolt (AN or NAS type) with the correct length we present a table for you to verify if the exact bolt is used.
These bolts are used in numerous applications throughout the aircraft and applying the correct bolt and using not too many washers means getting the right length. The table we provide should assist with that.
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 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:
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
The table below provides the standard AN bolt lengths.
For a more complete printable version click here.