The family side by side
| Standard | Nominal | Thread | Across flats, in | Head height, in | Grips listed, in |
|---|---|---|---|---|---|
| AN3 | 3/16 in | 10-32 UNF-3A | .365 – .377 | .109 – .141 | 1/16 to 4-1/4 |
| AN4 | 1/4 in | 1/4-28 UNF-3A | .428 – .440 | .140 – .172 | 1/16 to 5-13/16 |
| AN5 | 5/16 in | 5/16-24 UNF-3A | .490 – .502 | .172 – .204 | 1/16 to 5-7/16 |
| AN6 | 3/8 in | 3/8-24 UNF-3A | .553 – .565 | .203 – .235 | 1/16 to 5-13/16 |
| AN7 | 7/16 in | 7/16-20 UNF-3A | .615 – .627 | .234 – .266 | 7/16 to 5-7/16 |
| AN8 | 1/2 in | 1/2-20 UNF-3A | .740 – .752 | .265 – .297 | 7/16 to 4-9/16 |
From AN3 thru AN20 Rev. 12, sheets 1 and 2.
How to choose one
Diameter comes from the design: the drawing, the structural repair manual or the part being replaced. The standard number is the diameter in sixteenths of an inch: AN3 is 3/16, AN8 is 8/16.
Grip should match the thickness of the parts the bolt holds. AC 43.13-1B par. 7-37 allows a slightly longer grip made up with washers, up to 1/8 inch combined. The bolt grip calculator does that check.
Letters set material and drilling: C for corrosion-resistant steel, DD for aluminum alloy, H for a drilled head, A after the dash for an undrilled shank. The part number decoder reads any of them back to its row.
How to read the part number
| Part | Meaning |
|---|---|
| AN4 | Standard and nominal diameter: AN3 = 3/16 in, then one sixteenth per step (AN4 = 1/4 in, AN8 = 1/2 in). |
| C before the dash | Corrosion-resistant steel. Nothing here = non-corrosion-resistant steel. |
| DD before the dash | Aluminum alloy. |
| H before the dash | Drilled head (for safety wire). |
| -12 | Dash number: sets grip and length, read off the table. First digit whole inches, second digit eighths. |
| A after the dash | Undrilled shank. No A = shank drilled for a cotter pin. |
Limits — when NOT to use this
- Approved data governs. Use the bolt the maintenance manual or IPC calls for.
- Superseded standard. Cancelled by Notice 1 (Dec 1999) and superseded by NASM3 thru NASM20; the notice states the part numbers are identical.
- AN9 to AN20 are in the same standard but not in these sheets yet.
Sources
- AN3 thru AN20 Rev. 12, 14 Jan 1991 — Bolt — Machine, Aircraft — all dimensions, codes and examples on this page.
- FAA AC 43.13-1B, par. 7-37 — grip length and the washer limit.
Educational reference only. not approved data. Always consult the applicable SRM, AMM, or AC 43.13-1B and your certifying authority.