Spec Reference
MS20995 & NASM25173 lockwire: complete alloy and diameter guide
Seven wire types. Five diameters. One spec family. This guide explains how to read MS20995 part numbers, choose the right material for your environment, and understand the temperature and service limits that separate one lockwire alloy from another.
American Wire Works — Folcroft, PA — stocking safety wire since 1940
How to read a lockwire part number
Every MS20995 part number follows the same three-part pattern:
Base Specification
MS20995 — the mil-spec number, also published as NASM25173. Defines tensile, elongation, and coating requirements.
Alloy Suffix
One or two letters identifying the alloy: C, NC, N, CY, AB, or CU. See the suffix table below.
Diameter Code
Two-digit number equal to the wire diameter in thousandths of an inch. 20 = 0.020", 32= 0.032", etc.
Alloy suffix codes
| Suffix | Material |
|---|---|
| C | Stainless Steel 302/304 |
| NC | Monel 400 |
| N | Inconel / Oxidized Inconel |
| CY | Cadmium-Plated Copper |
| AB | Blue Anodized Aluminum |
| CU | Bare Copper |
Common diameters
| Diameter Code | Actual Diameter |
|---|---|
| 20 | 0.020" |
| 25 | 0.025" |
| 32 | 0.032" |
| 41 | 0.041" |
| 47 | 0.047" |
Alloy comparison table
All seven alloys stocked by American Wire Works, with temperature limits, target environment, and primary application.
| Alloy | Spec Code | Temp Limit | Environment | Use Case |
|---|---|---|---|---|
| Stainless Steel | MS20995C | 1,200°F (649°C) | General / Aerospace | Airframe fasteners, nacelles, landing gear, general MRO |
| Monel 400 | MS20995NC | 1,000°F (538°C) | Saltwater / Chloride | Naval vessels, offshore platforms, coastal equipment |
| Inconel | MS20995N | 1,600°F (871°C) | Extreme Heat | Turbines, exhaust manifolds, hot section hardware |
| Oxidized Inconel | MS20995N | 1,600°F (871°C) | Extreme Heat / Low Glare | Hot section hardware where visual inspection is required |
| Copper | MS20995CU | 400°F (204°C) | Electrical / Avionics | Circuit breakers, fluid caps, avionics panels |
| Cadmium-Plated Copper | MS20995CY | 400°F (204°C) | Anti-Galling | Applications requiring predictable breakaway torque |
| Blue Anodized Aluminum | MS20995AB / NASM25173 | 300°F (149°C) | Weight-Critical | UAV/drone frames, light aircraft, weight-sensitive assemblies |
When to use each alloy
Stainless Steel (MS20995C) — the aerospace default
Type 302/304 stainless is the most widely specified lockwire in aviation and industrial maintenance. It offers an excellent balance of tensile strength, corrosion resistance, and workability. Rated to 1,200°F, it covers the vast majority of airframe, nacelle, and landing gear fastener applications. When a spec sheet simply says "safety wire" without further qualification, stainless steel is almost always what is meant.
Shop Stainless Steellockwire →Monel 400 (MS20995NC) — the marine and offshore choice
Monel 400's nickel-copper alloy resists chloride-induced stress-corrosion cracking that can silently degrade stainless steel in saltwater service. It is the standard lockwire for naval surface combatants, offshore drilling equipment, and coastal industrial facilities. If your application involves spray, immersion, or extended exposure to salt air, Monel is the correct call over stainless.
Shop Monel 400lockwire →Inconel (MS20995N) — turbines and extreme heat
Inconel's nickel-chromium matrix retains its strength well beyond the limit of stainless steel, making it the required alloy for turbine hot sections, afterburner hardware, and exhaust manifold fasteners rated above 1,200°F. With a service limit of 1,600°F, it is specified wherever thermal degradation of a cheaper alloy would create a safety hazard.
Shop Inconellockwire →Oxidized Inconel — same heat rating, non-reflective finish
Oxidized Inconel shares the 1,600°F temperature ceiling of standard Inconel but carries a black, non-reflective surface treatment. The matte finish makes the wire easier to spot during visual inspections in high-glare environments and simplifies post-maintenance sign-off. It is the preferred choice when inspectors need to confirm wire presence quickly on polished or painted hot-section hardware.
Shop Oxidized Inconellockwire →Copper (MS20995CU) — avionics and electrical panels
Bare copper lockwire is soft, highly conductive, and non-magnetic. These properties make it the material of choice for securing circuit breakers, fuel cap vents, and avionics panel covers where galvanic compatibility or electrical continuity is a concern. Its lower tensile strength relative to steel means it is not used in high-vibration structural applications.
Shop Copperlockwire →Cadmium-Plated Copper (MS20995CY) — controlled breakaway torque
The cadmium plating on MS20995CY wire provides lubricity that reduces galling during installation and yields more predictable breakaway torque values. This makes it particularly useful in applications where maintenance crews need to confirm that a fastener has not been tampered with, or where consistent removal force is important for quality records.
Shop Cadmium-Plated Copperlockwire →Blue Anodized Aluminum (MS20995AB / NASM25173) — weight-critical platforms
At roughly half the weight of stainless steel, blue anodized aluminum lockwire is the standard choice for UAV and drone airframes, light sport aircraft, and any weight-critical assembly where every gram matters. The distinctive blue anodize provides a color-coded visual cue that simplifies inspection. Service temperature is limited to 300°F, so it is not suitable for engine-adjacent applications.
Shop Blue Anodized Aluminumlockwire →Frequently asked questions
What is MS20995 safety wire?+
How do I read the suffix codes in an MS20995 part number?+
Which lockwire alloy should I use in a saltwater or marine environment?+
What are the temperature limits for each lockwire alloy?+
Can I order safety wire in single cans or small quantities?+
Ready to order? Get a quote in minutes.
American Wire Works stocks all seven MS20995 alloys in standard diameters. Small cans, production spools, and mixed-alloy orders welcome. Tell us what you need and we'll respond same business day.