The five material families covered here handle 99% of aerospace fastener applications. Each one has a specific temperature envelope, strength class, corrosion profile, and application domain. The material stamped or etched on a bolt head isn't an upgrade option — it's a specification. Using the wrong material in an application designed for another is an engineering substitution, not a procurement decision. This guide gives you the foundation to recognize which material a drawing is calling for and why.
Material Selection Is a Design Decision
Before reaching for the parts bin, understand two things about any fastener application: what loads does the joint see, and what environment does it live in? Those two answers determine the material. A cadmium-plated alloy steel AN bolt is the right answer for the vast majority of airframe joints — but put it in an exhaust collector bracket and it will fail inside a maintenance cycle as the cadmium softens and the steel oxidizes. The engineering team that designed that bracket specified CRES or A286 for a reason.
When a plan or maintenance manual calls out a part number, the material is already encoded in that number. Your job is to match it — not upgrade, not substitute, not use what's in the bin because it looks similar. Use this guide to understand what you're looking at when the part number tells you.
Fastener Material Comparison
| Material | Common Specs | Tensile Strength | Temp Limit | Identifier |
|---|---|---|---|---|
| Cadmium-Plated Alloy Steel | AN3–AN20, MS20033 | ~125,000 psi | 450°F | Silver-gray, no special head marking |
| CRES 300-Series Stainless | AN4C, MS20365-C | ~125,000 psi | 800°F | "C" suffix, single raised dash on head |
| A286 (Iron-Nickel Superalloy) | NAS1304, SPS45 series | 180,000 psi | 1,200°F | Specific NAS/SPS p/n, silver finish |
| Inconel 718 (Nickel Superalloy) | NAS1348, SPS43 series | 220,000 psi | 1,400°F | Specific NAS p/ns, slightly magnetic |
| Titanium 6Al-4V | NAS6703–NAS6720 | 160,000 psi | 600°F continuous | Dull silver, lightweight, non-magnetic |
Cadmium-Plated Alloy Steel — The Workhorse
The AN3–AN20 bolt series is 4130 or 4140 alloy steel, quenched and tempered to a minimum tensile strength of approximately 125,000 psi. The cadmium plating specification is AMS QQ-P-416, typically Type II (chromate conversion coat over cadmium), Class 2 (0.0005" minimum deposit thickness). This is the silver-gray hardware in every A&P's parts drawers and the baseline for AC 43.13-1B torque tables.
- Most common fastener material in EAB and MRO work: AN3-7 bolts, AN365/MS20365 self-locking nuts, AN310 castle nuts
- Not compatible with high-temperature zones (exhaust, turbine section): cadmium begins to soften and oxidize above 450°F
- Not for use in marine environments without additional sealant protection — cadmium corrodes in salt spray over time, despite reasonable initial salt-spray test ratings
- Do not weld or cut cadmium-plated hardware: cadmium oxide fumes above approximately 325°C are toxic. Full ventilation and respiratory protection required for any hot work near cadmium-plated parts.
CRES 300-Series Stainless
Austenitic stainless steel — the 18-8 family (18% chromium, 8% nickel minimum) — is non-magnetic in the annealed state and has very good corrosion resistance from its passive chromium oxide surface layer. Tensile strength is approximately the same as cadmium-plated alloy steel AN equivalents, making it suitable for any structural application where the alloy steel hardware is sized correctly.
- Identified by the "C" suffix in the part number: AN4C-7 is a 1/4-28 CRES bolt, grip 7/16". A single raised dash on the head face is also a standard CRES identification mark.
- Use in: fuel systems, hydraulic fittings, wet compartments, bilge areas, saltwater-adjacent applications, lavatory hardware, galley structure
- Not appropriate for high-temperature proximity: CRES passivates well, but thermal cycling above 800°F causes sensitization (chromium carbide precipitation at grain boundaries), reducing corrosion resistance and fatigue life
- CRES fasteners should carry AMS 2700 passivation certification for use in certified aircraft — see our corrosion finishes guide for passivation details
A286 — Elevated Temperature Structural
A286 is an iron-nickel-chromium superalloy that retains useful strength at temperatures where alloy steel and stainless begin to lose their mechanical properties. It is precipitation-hardened — heat treated to develop 180,000 psi minimum tensile strength — and usable for continuous structural duty to approximately 1,200°F.
- Primary applications: turbine case bolts, afterburner section hardware, hot section structural fittings, exhaust collector mounting in turboprop and turbofan engines
- AMS 5731 (bar stock) and AMS 5732 (forgings) govern the base material; heat treatment is critical — parts must carry heat treatment certifications documenting the solution anneal and aging cycle
- Found in NAS1304 series and SPS45 series fasteners; magnetic identification is not reliable for A286 — it can be slightly magnetic depending on processing history, unlike austenitic stainless
- When ordering surplus A286 hardware, verify the lot traceability includes the heat treatment documentation — the same part number without proper heat treat certs is a different (and non-airworthy) product
Inconel 718 — Hot Section Hardware
Inconel 718 is a nickel-chromium-molybdenum-niobium superalloy that maintains structural integrity at the highest temperatures encountered in aerospace fastener applications. At 220,000 psi tensile with a 1,400°F continuous service limit, it is the material of choice for turbine hot section hardware where both extreme temperature and high sustained load coexist.
- Stage 1 and 2 turbine blade attachment hardware, combustion chamber structural bolts, augmentor (afterburner) structural fittings in military engines
- AMS 5662 (sheet/plate/bar) and AMS 5663 (bar, higher strength) govern the base material; age hardening at 718°F and 1,150°F is the standard two-stage treatment
- Heavier than titanium by approximately 45% — used where the thermal resistance requirement outweighs the weight penalty
- MIL-S-8879 (now SAE AS8879) unified thread form is frequently specified with Inconel 718 fasteners due to the fatigue environment they operate in
- Slightly magnetic due to small amounts of ferrite or delta phase in the microstructure — distinguishable from A286 by density (denser) and from alloy steel by non-sparking behavior when struck
Titanium 6Al-4V — Weight-Critical Primary Structure
Titanium 6Al-4V (6% aluminum, 4% vanadium) delivers 160,000 psi tensile strength at roughly half the weight of alloy steel. The strength-to-weight ratio is the design driver — titanium fasteners allow the same structural performance at approximately 40% of the mass penalty of equivalent alloy steel hardware.
- Applications: airframe primary structure on weight-critical aircraft, composite spar fittings (titanium is galvanically compatible with carbon fiber, unlike aluminum and steel), wing attach on high-performance homebuilts, nacelle structure
- Temperature limit is approximately 600°F continuous, 800°F for short duration. Do not use in exhaust proximity or engine hot sections — the material begins to absorb hydrogen and oxygen at elevated temperatures, causing embrittlement.
- AMS 4928 governs bar stock, AMS 4965 governs forgings; fastener standards are NAS6703 through NAS6720 (close-tolerance titanium alloy bolts)
- Non-magnetic — use a magnet as a quick field check to distinguish titanium from alloy steel or stainless (both will attract a magnet; titanium will not)
- ITAR-controlled for certain titanium alloy fastener forms. Verify export classification before quoting international orders — see your freight forwarder's guidance or contact us at service@aerospacespecbolt.com for ITAR compliance questions.