At MF Supply, we specialize in sourcing and delivering certified Mil-Spec fasteners governed by MIL-STD requirements established by the US Department of Defense (DOD) and administered by the Defense Logistics Agency (DLA).
Mil-Spec hardware isn’t just “stronger” or “higher quality.” It’s manufactured, tested, inspected, and documented to ensure repeatable performance, exacting paperwork and audit-ready compliance, lot after lot, program after program. Strength, dimensions, materials, finishes, inspection criteria, and documentation are all defined long before a part ever reaches production.
For aerospace, defense, and precision manufacturers, the wrong interpretation of a part number, finish, or country-of-origin requirement can lead to compliance issues, production delays or worse.
That’s why we’ve compiled answers to the most common/frequent Mil-Spec fastener questions we hear from engineers, program managers, and procurement teams every week. The questions that surface during design, procurement, supplier audits, alternates approvals, and “why did this part get rejected?” moments.
In Part 1 of this four-part series, we cover the fundamentals:
- What actually makes a fastener truly Mil-Spec
- How Mil-Spec compares to commercial hardware (with a real-world example)
- The most common standards you’ll encounter (AN, MS, NAS/NASM)
- How to quickly identify a Mil-Spec part number
- What “Made in the USA” does, and does not, mean in practice
Think of this as the foundation, before alternates are approved, or auditors start asking uncomfortable questions.
Part 1
1. What is a Mil-Spec fastener?
Mil-Spec (Military Specification) fasteners or MIL-STD fasteners are hardware components that meet specific standards set by the US Department of Defense (DOD). These fasteners are used in critical military, aerospace, and defense applications where reliability, traceability, and performance are essential.
2. What makes a fastener “Mil-Spec”?
A fastener is considered “Mil-Spec” when it meets strict US military standards for tensile strength, hardness, material, plating, dimensions, quality, and performance. These fasteners are made to precise specifications, often with specialized coatings, and must pass rigorous testing and inspection. They come with full traceability and certification to ensure reliability in mission-critical applications. True Mil-Spec fasteners are produced only by approved manufacturers and backed by documentation.
3. What is the difference between Commercial and Mil-Spec Fasteners?
Mil-spec fasteners look a lot like their civilian/commercial cousins, but these little guys are made to specific standards that define in detail the fasteners’ attributes, including dimensions, tensile strength, hardness, threads, drive type, material qualities, plating/finish, and more. Mil-spec fasteners are even traceable by lot to designated manufacturers. The Qualified Suppliers List for Manufacturer’s [QSLM] is a government-maintained list of Manufacturers certified to make Mil-Spec fasteners according to the highest quality standards—commercial fasteners are not held to such specific and exacting standards.
4. Do Mil-Spec fasteners have different features and standards than commercial fasteners?
Mil-Spec parts are manufactured and tested to strict military standards to ensure performance and reliability. In general, commercial fasteners will not have the exact same quality standards. Let’s look at a specific example and compare the Mil-Spec MS24693-C4, (sometimes referred to as MS24693C4 or MS24693C-4) which is a 4-40 x 3/8 Phillips flat 100 degree machine screw in 300 series stainless steel, to its commercial cousin.
Features of MS24693C-4:
- Manufactured in a QLSM approved factory
- Made/melted in the USA or other DFARs* approved country
- Materials to procurement spec FF-S-92, SAE AIR 4127
- Cleaned, descaled, passivated to AMS-QQ-P-35; AMS 2700
- Dimensions, tensile, hardness, threads, recess, head marking to AN, MS, NAS, NASM standards
- Magnetic permeability to test specs ASTM A342
- Quality Assurance to procurement spec FF-S-92 MIL-STD 1312
- Inspection system requirements per Mil-I-45208
- Full lot traceability, manufacturer’s certification, chemical and physical certification
- Available in diameters from #0 through 1/4 inch in coarse and fine thread and various lengths
Features of 4-40 x 3/8 commercial Phillips flat 100 degree machine screws in 18-8 series stainless steel:
- Manufactured per ASME B18.6.3-2002
- Thread dimensions per ASME B1.1
As you can see, the Mil-spec version is held to a higher and more exacting level of quality and testing than the commercial version. As such, the Mil-spec parts are cleaned and passivated, and tested for magnetic permeability, whereas the commercial parts don’t have this requirement.
5. What are the most common Mil-Spec standards?
The most common Mil-Spec fastener designations include:
- AN – Army/Navy Aeronautical
- MS – Military Standard
- NAS & NASM – National Aerospace Standard
6. How can I identify a Mil-Spec fastener?
Look for part numbers starting with MS, NAS, or AN, which indicate the applicable standard.
7. Are Mil-Spec fasteners always made in the USA?
Not necessarily. However, fasteners required to meet DFARS compliance must be made from specialty metals that are melted and manufactured in qualifying countries, including the USA.
If you take only one thing from these first seven questions, let it be this: true Mil-Spec fasteners are produced only by approved manufacturers and backed by documentation. And while “USA-made” is sometimes assumed, DFARS requirements are tied to specialty-metal sourcing/melt and qualifying countries, not a blanket label, so it’s worth confirming early. In Part 2, we’ll go deeper on DFARS, specialty metals, and the documentation stack (COCs, MTRs, plating/heat-treat certs, inspection reports) that often determine whether parts pass review.
In the meantime, if you have any questions, feel free to Connect with our team or send us a request for quote and our team of sourcing experts will help you find what you need. “Finding the right screw for you” is our tag line after all!
Related:
- Buyer’s Guide to Mil-Spec Fasteners
- Mil-Spec DFARS!? What the heck is that?
- Mil-Spec Fasteners Guide: Frequently Asked Questions
Book a one-on-one consultation with our President, Robin, to discuss how MF Supply can help you solve your Industrial Sourcing, Fastener, and Safety concerns.
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MF Supply is a WBE/WOSB certified supply chain partner to business, industry and government. We are sourcing experts and stocking distributors of Hardware, Precision & Mil-Spec Fasteners and Safety supplies. For more than 50 years, we have been supplying manufacturers in the electronics, industrial, commercial, aerospace and military markets with the full range of fastener products and services. Our Cage Code is 58QG4 and our registered name is RL Supply Inc dba MF Supply.