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🔗 Safety Wire Size Guide
Quick reference for safety wire gauge selection, common applications, and installation requirements per AC 43.13-1B and manufacturer guidance.
Safety Wire Gauge Reference
| Wire Size | Diameter | Material | Common Applications | Notes |
|---|---|---|---|---|
| .020" | 0.020" | Stainless Steel / Inconel / Copper | Small screws and fasteners in low-vibration areas, cowling fasteners, small drain plugs, instrumentation fittings, carburetor screws on small GA aircraft | Lightest common wire. Use when hole size or fastener size is small. Not suitable for high-load or high-vibration applications. |
| .025" | 0.025" | Stainless Steel / Monel | Medium-sized bolts and screws, access panels, small hydraulic fittings, lighter accessory mounting hardware on piston engines | Good general-purpose size for moderate applications. Often used on light aircraft where .032" would be oversized. |
| .032" | 0.032" | Stainless Steel (most common) | Standard for most turbine engine applications, oil plugs, hydraulic fittings, brake assemblies, structural fasteners, engine accessory gearbox hardware, AN/MS bolts and nuts | The most widely used size in commercial aviation maintenance. Specified by most AMMs when no specific size is listed. Per AC 43.13, this is the default for most turbine engine work. |
| .041" | 0.041" | Stainless Steel / Inconel | High-vibration applications, large fasteners, main rotor bolts on helicopters, high-temperature zones, large hydraulic system fittings, main landing gear hardware, structural bolts | Heaviest standard safety wire. Requires heavier-duty pliers. Do not over-twist — wire can snap if torqued too tightly. Specified by AMM or SRM when needed. |
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Wire Material Reference
| Material | Spec / Part Number | Temp Range | Use Case |
|---|---|---|---|
| Stainless Steel (304) | MS20995C (various sizes) | Up to ~1400°F short-term | General aviation maintenance — the standard for most work |
| Stainless Steel (316) | MS20995 | Up to ~1600°F | Corrosive environments, marine operations |
| Inconel / Nickel Alloy | MS20995N | Up to ~2000°F | High-temperature turbine zones, exhaust hardware, hot section bolts |
| Monel | MS20995M | Moderate | Corrosion-resistant applications, some fuel and hydraulic fittings |
| Copper | MS20995Cu | Low to moderate | Soft fittings that could be damaged by harder wire; some older aircraft |
Twist Requirements (AC 43.13-1B)
- Pigtail (twisted end): 4–6 twists per inch (do not over-twist)
- Single-wire method: pass through one hole, twist together
- Double-wire method (most common): thread two separate pieces, twist together with pliers
- Wire must be taut — slack wire provides no locking function
- Direction of wrap must resist the loosening direction of the fastener
- Cut and fold pigtail to avoid sharp ends that can snag and puncture gloves
General Rules
- Maximum span between safety wire holes: 24 inches
- Cluster limit: no more than 3 fasteners per wire run
- Never reuse safety wire — always use new wire
- Use calibrated torque wrench before safety-wiring — do not advance a fastener to reach a wire hole
- Pigtail minimum length: 1/2" to 1", tucked/bent back against wire
- Never use soft steel or galvanized wire on aircraft
Recommended Tools
- Safety wire pliers — Snap-On, Milbar, or equivalent aircraft-grade pliers
- Wire reels — 1 lb spools of MS20995C32 (.032") or C20 (.020")
- Diagonal cutters — flush cut for clean pigtail termination
- Wire holder / spool stand — keeps wire tangle-free during use
- Inspection mirror — verify wire direction on hard-to-see fasteners