Aircraft Fastener Identification and Selection

1. 1 Hardware numbering systems Hardware Identification Systems: AN, MS, and NAS.
2. 2 Bolt and screw markings Bolt and Screw Identification and Head Markings.
3. 3 Nuts, washers and pins Nut, Washer, and Pin Identification.
4. 4 Rivet identification Rivet Identification and Material Codes.
5. 5 Compatibility and substitution Material Compatibility and Substitution Authority.

• ✓Decode standard part numbers.
• ✓Interpret head markings.
• ✓Verify material compatibility.
• ✓Match the engineering call-out.

The IPC calls out NAS6204-6 for a flap hinge. The shop bin holds AN4-6A bolts with the same 1/4-inch diameter and thread, and they fit the hole. What should the technician install?

AI Stuck? In the course, Crew Chief, your AI tutor, explains it.

• 14 CFR §43.13(a)performance rules: methods, techniques and practices prescribed by the manufacturer, or other methods acceptable to the Administrator, the basis of the course's substitution rules.
• FAA AC 43.13-1B w/CHG 1, Chapter 7aircraft hardware: head markings (paragraph 7-36, Figure 7-1), bolt, screw, nut, washer and pin rules, and identification Tables 7-10 to 7-15.
• FAA AC 43.13-1B w/CHG 1, Chapter 4 Section 4rivet identification (Table 4-8), rivet part number breakdown (Figure 4-4) and rivet formation (Figure 4-7).
• FAA AC 43.13-1B w/CHG 1, Chapter 6 Section 5dissimilar-metal (galvanic) contact and protective coatings, used with the SRM to confirm a fastener suits the parent structure.
• AIA NAS and NASM specificationsthe Aerospace Industries Association (AIA) sheets used to decode NAS and NASM part numbers, including modern close-tolerance and high-strength hardware.
• FAA AC 20-71, paragraph 7dual locking devices on fasteners, cited with the rule that self-locking nuts are not used on parts subject to rotation.

Who is this course for?

Airframe and powerplant maintenance technicians, aircraft maintenance engineers, structural repair mechanics and apprentice mechanics who perform or supervise hardware selection on FAA type-certificated aircraft. You need basic familiarity with 14 CFR Part 43, hand tool use, and access to the aircraft's Maintenance Manual, SRM and IPC.

How do I read an AN bolt number?

The number after AN is the diameter in 1/16 inch, so AN3 is 3/16 inch and AN4 is 1/4 inch. The dash number is the bolt length measured from under the head: the last digit is eighths of an inch and any leading digit is whole inches, so AN3-7 is 7/8 inch long and AN3-12 is 1-1/4 inches long. A trailing A means an undrilled shank, H means a drilled head, and no A means a drilled shank for a cotter pin or safety wire, while MS and NAS bolt numbers follow their own specification sheets.

What do bolt head markings mean?

Per AC 43.13-1B paragraph 7-36 and Figure 7-1, a raised dash or asterisk marks an AN standard steel bolt, a single dash corrosion-resistant steel, and two raised dashes an AN aluminum-alloy bolt. A raised or recessed triangle marks a close-tolerance NAS bolt. Bolts with no markings are low strength, and an unmarked or illegible bolt is rejected.

Where can't I use a self-locking nut?

Per AC 43.13-1B paragraph 7-64, self-locking nuts are not used on parts subject to rotation, or where a loose nut could fall or be drawn into a turbine engine air intake scoop. Fiber or nylon self-locking nuts are not installed where temperatures exceed 250 °F, and all-metal self-locking nuts are primarily used in high-temperature areas.

Which fasteners go into carbon-fiber composite structure?

Cadmium-plated steel fasteners must not be installed in carbon-fiber composite, because the carbon promotes severe galvanic attack on the cadmium plating. Titanium (Ti-6Al-4V, NAS6303 series) or A286 stainless fasteners are the typical compatible choices per the airframer's SRM. Where the SRM calls for a wet installation with corrosion-inhibiting sealant, such as MIL-PRF-81733, that barrier must not be omitted.

When can I substitute a different fastener?

If the IPC lists an alternate, either part is acceptable as called out. If it does not, the substitution needs data acceptable to the FAA under 14 CFR §43.13(a), such as a manufacturer's service bulletin, an STC or a DER-approved Form 8110-3, and approved data when the change is a major repair or alteration. Verbal approvals, bin equivalents and assumptions of equivalence are not acceptable data. Record the part number actually installed in the maintenance entry.