MS / NAS Fastener Callouts
Aerospace hardware is defined entirely by its part number — series, diameter, grip, material and finish are all encoded. Substituting commercial hardware is both a structural and a certification problem.
Common families
| Part number | Type | Notes |
|---|---|---|
| AN3 – AN20 | Bolt, hex head | Legacy Army-Navy general-purpose airframe bolt |
| AN173 – AN186 | Bolt, close tolerance | Reamed-hole shear applications |
| AN525 / MS27039 | Screw, structural washer head | Common airframe screw |
| MS20470 | Rivet, universal head | Solid rivet, the airframe workhorse |
| MS20426 | Rivet, 100° countersunk | Flush external surfaces |
| MS21042 / MS21044 | Nut, self-locking | Reduced hex, all-metal / nylon insert |
| NAS1103 – NAS1120 | Bolt, close tolerance hex | Higher strength than AN, tighter tolerance |
| NAS6203 – NAS6220 | Bolt, close tolerance | A286 / alloy steel, high strength |
| NAS1149 | Washer, flat | Standard airframe washer series |
| NASM (ex MS) | — | MS numbers migrated to NASM under SAE custody |
Decoding a callout
| Element | Example | Meaning |
|---|---|---|
| Series prefix | AN / MS / NAS / NASM | Which standard defines it |
| First numeral group | e.g. AN4 | Diameter in 1/16 inch — AN4 = 4/16 = 1/4" |
| Dash number | e.g. -13 | Grip length (unthreaded shank), usually 1/8" steps |
| Suffix A | AN4-13A | No cotter-pin hole drilled |
| No suffix | AN4-13 | Drilled shank for a cotter pin |
| Suffix C | …C | Corrosion-resistant steel |
| Suffix DD | …DD | 2024-T4 aluminium (rivets) |
Grip length must match the stack so threads never bear in shear. See the fastener selection guide, and get joint allowables from the rivet tool. Always confirm the current revision on ASSIST (quicksearch.dla.mil).
A reference aid, not a substitute for engineering judgment. Verify against the governing standard.