Lockwire Basics
What Is Lockwire? Locking Wire & Safety Wire Explained
Lockwire — also called lock wire, locking wire, or safety wire — is soft, ductile wire threaded through drilled fasteners and twisted so vibration cannot rotate them loose. Here is what it is, why aviation and industry depend on it, and how to choose the right material and size.
American Wire Works — Folcroft, PA — stocking safety wire since 1940
Lockwire, lock wire, locking wire, safety wire — one product, four names
Lockwire is a mechanical locking device in its simplest form: a length of soft, ductile wire passed through small holes drilled in bolt heads, drilled nuts, turnbuckles, or fittings, then twisted and tensioned so that any loosening rotation of the fastener pulls the wire tighter. The fastener physically cannot back out without first breaking the wire — which the wire's tensile strength prevents under normal vibration.
The terminology varies by industry, but the product does not. U.S. aviation mechanics typically say safety wire; military, motorsport, and international communities often say lockwire, lock wire, or locking wire. Aircraft locking wire, aviation safety wire, and mil-spec lockwire all describe the same wire — usually manufactured to the MS20995 / NASM25173 specification.
Why locking wire is used
Locking wire is specified wherever a loosening fastener would be catastrophic — not merely inconvenient. Thread-locking compounds and lock washers can fail under sustained vibration and heat; a correctly installed wire provides a positive, visually inspectable lock.
Aviation & Aerospace
Aircraft locking wire secures engine accessories, fluid fittings, turnbuckles, and drilled-head bolts throughout airframes and powerplants. Installation practices follow FAA Advisory Circular AC 43.13-1B, and the wire itself is specified by drawing — typically MS20995.
Motorsport
Racing sanctioning bodies require safety wire on oil drain plugs, brake caliper bolts, and other critical fasteners. A wired fastener cannot vibrate loose mid-race, and scrutineers can verify it at a glance.
Defense
Military aircraft, naval vessels, ordnance, and ground vehicles use mil-spec lockwire on hardware subjected to shock and vibration. Procurement documents call out MS20995 or NASM25173 part numbers.
Industrial
Turbines, compressors, pumps, and heavy rotating equipment rely on locking wire for fastener retention where unplanned downtime or a thrown bolt would be dangerous and expensive.
What lockwire is made of
The alloy determines the temperature limit and the environments the wire can survive. These are the materials buyers specify most often.
| Material | Temp Limit | Best For |
|---|---|---|
| Stainless Steel 302/304 | 1,200°F (649°C) | General aviation, airframes, industrial MRO — the default choice |
| Monel 400 | 1,000°F (538°C) | Marine, offshore, and corrosive chloride environments |
| Inconel 600 | 1,600°F+ (871°C+) | Turbine hot sections, exhaust manifolds, extreme heat |
| Cadmium-Plated Copper | 400°F (204°C) | Breakaway applications and anti-galling installations |
| Blue Anodized Aluminum | 300°F (149°C) | Weight-critical assemblies — UAVs, drones, light aircraft |
| Bare Copper | 400°F (204°C) | Electrical panels, circuit breakers, avionics covers |
Not sure which alloy your application needs? Start with stainless steel lockwire for general work, Monel lockwire for saltwater, and Inconel lockwire for extreme heat.
The specs behind lock wire: MS20995, NASM25173, and MS9226
Most locking wire is purchased against MS20995, the U.S. military specification that defines alloy, diameter, tensile strength, and elongation. The part number is easy to read: the letter suffix identifies the alloy (C = stainless, NC = Monel, N = Inconel) and the trailing number is the diameter in thousandths of an inch — so MS20995C32is stainless steel at 0.032". The spec is also published as NASM25173, and Inconel wire for hot sections is often called out as MS9226 / AMS 5687.
Common lockwire sizes
Five diameters cover nearly every application. 0.032" is by far the most commonly ordered size.
| Diameter | Typical Use |
|---|---|
| 0.020" | Small fasteners, avionics panels, tight bolt-head holes |
| 0.025" | General aviation and light maintenance work |
| 0.032" | Most common — AN/NAS bolts, airframe and engine accessories |
| 0.041" | Heavy fasteners and structural applications |
| 0.047" | High-load industrial and defense hardware |
How lockwire works: the double-twist method
The wire is threaded through the drilled hole in one fastener, crossed, and twisted at 6–8 twists per inch with safety wire pliers, then routed taut to the next fastener. The critical rule: the wire must be oriented so that any loosening rotation of the fastener tightens the wire. Installed correctly, the fasteners brace each other — neither can rotate loose without breaking the wire.
Step-by-step safety wiring guide →Frequently asked questions
What is lockwire?+
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What is lockwire made of?+
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Need lockwire? Get a same-day quote.
American Wire Works stocks the full MS20995 / NASM25173 / MS9226 range — every alloy, every standard diameter. Family-owned and manufacturing in Folcroft, PA since 1940. Call (215) 744-6600 Mon–Fri 7:30am–3:30pm ET, or send a request and we'll respond same business day.
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