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Mil-Spec Fasteners Guide: Frequently Asked Questions About Military Standard (MIL-STD) Hardware


At MF Supply, we specialize in sourcing and delivering certified Mil-Spec fasteners including MIL-STD standards set by the US Department of Defense (DOD) and maintained by the Defense Logistics Agency (DLA). Below are answers to the most common questions we hear from customers in aerospace, defense, and precision manufacturing.


Mil-Spec Fasteners Guide - Quick Navigation. .

  1. What is a Mil-Spec fastener?
  2. What makes a fastener “Mil-Spec”?
  3. What is the difference between Commercial and Mil-Spec Fasteners?
  4. Do Mil-Spec fasteners have different features and standards than commercial fasteners?
  5. What are the most common Mil-Spec standards?
  6. How can I identify a Mil-Spec fastener?
  7. Are Mil-Spec fasteners always made in the USA?
  8. What does DFARS compliance mean?
  9. What materials are DFARS eligible?
  10. More about DFARS
  11. How do I know if a fastener is Mil-Spec certified?
  12. What paperwork comes with Mil-Spec fasteners?
  13. How do I read a Mil-Spec part number?
  14. Where can I get a print of a Mil-Spec part number?
  15. Where can I find a list of Mil-spec fasteners and specs?
  16. What types of Mil-Spec fasteners are available?
  17. What materials are Mil-Spec fasteners made from?
  18. How do I know if the metal meets DFARS requirements?
  19. Can I use a commercial equivalent instead of a Mil-Spec fastener?
  20. What is a “functional equivalent” fastener?
  21. How do I cross-reference a Mil-Spec fastener to a commercial or OEM part?
  22. How do I cross-reference a commercial or OEM part to a Mil-Spec fastener?
  23. What’s the typical lead time for Mil-Spec fasteners?
  24. Can I buy Mil-Spec fasteners in small quantities?
  25. What industries use Mil-Spec fasteners?
  26. What finishes or platings are available for Mil-Spec fasteners?
  27. What happens if a Mil-Spec fastener fails inspection?


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.


8. What does DFARS compliance mean?

DFARS (Defense Federal Acquisition Regulation Supplement) compliance ensures that the specialty metals used in the fasteners are sourced and manufactured from approved countries. DFARS is often required for Defense Department related contracts.


9. What materials are DFARS eligible?

DFARS only pertains to fasteners made from “specialty metals” including stainless steel, high alloy steel, like Grade-BD, or Grade 5 Chromium steel with high chromium content. “Specialty metals” means:

  1. Steel:
    • With a maximum alloy content exceeding one or more of the following limits:
      • 1.65% Manganese
      • 0.60% Silicon
      • 0.60% Copper

    • Containing more than 0.25% of any of the following elements:
      • Aluminum
      • Chromium
      • Cobalt
      • Molybdenum
      • Nickel
      • Niobium (Columbium)
      • Titanium
      • Tungsten
      • Vanadium

  2. Metal alloys consisting of:
    • Nickel or iron-nickel alloys that contain a total of alloying metals other than nickel and iron in excess of 10%.
    • Cobalt alloys that contain a total of alloying metals other than cobalt and iron in excess of 10%.

  3. Titanium and titanium alloys
  4. Zirconium and zirconium alloys

“Steel” means an iron alloy that includes between .02 and 2 percent carbon and may include other elements.

Restriction: Except as provided in paragraph (c) of this clause, any specialty metals incorporated in items delivered under this contract shall be melted or produced in the United States, its outlying areas, or a qualifying country.


10. More about DFARS

Almost a decade ago, the term “DFARS Compliant Material” came to the forefront for companies supplying parts and services to the government. The original Federal Acquisition Regulation (FAR) clause 252.225-7014 specified “A Preference for Domestic Specialty Metals.”  What that means in our world is that for fasteners to be DFARS compliant, the metal used to fabricate them must be melted or manufactured in the United States or a qualifying country.

Qualifying countries: Australia, Austria, Belgium, Canada, Czech Republic, Denmark, Egypt, Finland, France, Germany, Greece, Israel, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, Turkey, United Kingdom of Great Britain and Northern Ireland. Visit the DPC website, section 252.225, or the ACQ website to keep up to date with DFARs requirements, which were updated January 2023. To learn more about DFARS as it pertains to Mil-Spec fasteners, refer to this link.


11. How do I know if a fastener is Mil-Spec certified?

Mil-Spec fasteners are commonly supplied with a manufacturer’s Certificate of Conformance (COC) referencing the part number which calls out the standard the fastener is made to.


12. What paperwork comes with Mil-Spec fasteners?

Although Mil-Spec fasteners are commonly provided with the Manufacturer’s Certificate of Conformance (COC), other paperwork such as Material Test Report (MTRs), Plating or Heat Treatment Certifications, DFARS certification, Lot traceability or Dimensional Test reports may also be available and sometimes involves a fee.

Here is a more extensive list of paperwork that might accompany Mil-spec fasteners:

  1. Manufacturer’s Certificate of Conformance (COC)
    • Verifies that the parts meet the specified Mil-Spec standard
    • Should include part number, lot number, specification, and manufacturer info
  2. Material Test Reports (MTRs) (if required)
    • Confirms the chemical and mechanical properties of the raw material
    • Typically needed for DFARS compliance or aerospace contracts
  3. DFARS Compliance Statement (if applicable)
    • Required if your project is subject to DFARS specialty metals clause
    • Should confirm country of melt and manufacture is DFARS-approved
  4. Plating or Finish Certifications (if applicable)
    • Certifies any surface treatments (e.g., cadmium, zinc, passivation) meet required specs
  5. Heat Treat Certification (for heat-treated parts)
    • Confirms the heat treatment process meets the Mil-Spec requirements
  6. Dimensional or Inspection Reports (on request or for critical parts)
    • Documents that parts were inspected and meet dimensional tolerances
  7. Lot Traceability
    • Ensures all fasteners in your order can be traced back to the original manufacturing lot
    • Critical for quality audits and failure investigations

Note: Although Mil-Spec fasteners are commonly provided with the Manufacturer’s Certificate of Conformance (COC), other paperwork such as Material Test Report (MTRs), Plating or Heat Treatment Certifications, DFARS certification, Lot traceability or Dimensional Test reports must be specifically requested and sometimes involves a fee.


13. How do I read a Mil-Spec part number?

Each character in the part number provides information about the size, material, thread, and finish. For example, MS24693C4, sometimes expressed MS24693-C4 or MS24693C-4 is a 4-40 x 3/8 Phillips Flat 100 Degree Machine Screw in 300 Series Stainless Steel. Contact us if you need help decoding a part number.


14. Where can I get a print of a Mil-Spec part number?

Documentation for MIL-STD parts are maintained by the Defense Logistics Agency (DLA). The Aerospace Industries Association (AIA) has a database of prints available for purchase.


15. Where can I find a list of Mil-spec fasteners and specs?

The Defense Logistics agency (DLA) is a great resource. They maintain a comprehensive database of specifications and drawings. They also maintain a catalog of hardware that includes National Item Identification Numbers (NIIN) and National Stock Numbers (NSN) that are sometimes called out in a bill of materials. Check out the following links for more comprehensive information regarding hardware:


16. What types of Mil-Spec fasteners are available?

We supply a full range of Mil-Spec/MIL-STD fasteners, including:

  • Chisel Point Cotter Pins : MS9245.
  • Dowel Pins : M21143, MS16555, and MS16556.
  • Hex Head Cap Screws : MS35307, MS35308, MS90725, and MS90726.
  • Helical Inserts : MA3279, MA3329, MS121, MS122, MS124, and MS21209.
  • Keenserts Style Threaded Inserts :MS51830, MS51830A, MS51830CA, MS51831, MS51831A, MS51831CA, MS51832, MS51832A, MS51832CA, NA0146, NA0147, NA0148, NA0149, NA0150, NA0151, NAS1394, and NAS1395.
  • Nuts : MS17830, MS35649, MS35650, MS51967, MS51967B, MS51967C, MS51971, MS51972, NAS17830, NAS662C, NAS671, and NAS671C.
  • Machine Screws : AN500AD, AN501AD, AN526C, MS24693, MS24693C, MS35190, MS35191, MS35206, MS35207, MS35265, MS35266, MS35275, MS35276, MS51957, MS51958, MS51959, MS51960, NAS1635, NAS1801, and NAS662C.
  • Retaining Rings : MS16624 and MS16625.
  • Self-Tapping Screws & Drive Screws : MS51861, MS51861C and MS21318.
  • Shoulder Screws : MS51575 and MS51576.
  • Socket Head Cap Screws/Bolts : MS16995, MS16996, MS16997, MS16998, MS51576, NAS1351C, NAS1352C, NAS1351N, NAS1352N, and MS24671.
  • Socket Set Screws : AN565, NAS1081, MS180, MS213, MS510, MS514, and MS519.
  • Slotted Spring Pins : MS16562.
  • Standoffs and Spacers: NAS42, NAS43, NAS61, NAS1056, NAS1057, NAS1829, NAS1831, NAS1831, NAS61.
  • Washers : AN960, AN960-C, AN960-CL, AN960-L, AN970, MS15795, MS27183, NAS1149, NAS620, MS35333, MS35335, MS35338, and MS51848.
  • Can’t find the product you’re looking for? Contact us for more!


17. What materials are Mil-Spec fasteners made from?

Mil-Spec fasteners are available in a wide variety of materials and platings. Common materials include:

  • Carbon Steel
  • Stainless steel (302, 304, 316, 400 Series, A286)
  • Alloy steel
  • Inconel
  • Monel
  • Brass

Material, plating and finish requirements are usually defined in the part specification.


18. How do I know if the metal meets DFARS requirements?

Only specialty metals are DFARS eligible. DFARS-compliant parts must come with documentation stating the country of melting and manufacturing.
If you haven’t already, check out questions 9 and 10. They explore DFARS and specialty metals in greater detail, including which materials are subject to DFARS requirements.


19. Can I use a commercial equivalent instead of a Mil-Spec fastener?

Because some Mil-Spec fasteners may not be available off the shelf and may involve a long lead time, some manufacturers substitute commercial or OEM brand name fasteners for Mil-Spec parts. Proceed with caution when using functional equivalents for Mil-spec fasteners, and make sure to first get approval from your engineering or quality team. Functional equivalent commercial versions of MIL-STD fasteners may not have full traceability or certification and may not have passed the rigorous testing required of Mil-spec hardware.


20. What is a “functional equivalent” fastener?

A functional equivalent fastener matches the form, fit, and function of a Mil-Spec or OEM branded part but may not be manufactured to the same certifying standard or with the certified paperwork available with Mil-Spec hardware. These are often used for commercial or non-critical applications.


21. How do I cross-reference a Mil-Spec fastener to a commercial or OEM part?

Start by referring to our cross-reference charts. Alternatively, provide us with the Mil-Spec number, size, material, any special features, and we’ll identify equivalent options from brands like Holo-Krome, PIC-Design, Alcoa or others.


22. How do I cross-reference a commercial or OEM part to a Mil-Spec fastener?

We can help. Not all commercial or OEM parts have Mil-Spec equivalents. Provide the description including the size, dimensions, material, any special features, and we’ll identify if a Mil-spec option is available.


23. What’s the typical lead time for Mil-Spec fasteners?

Common Mil-Spec fasteners may be available off-the-shelf and may ship same day. Non-common sizes and materials may have extended lead times of 50 weeks or more. Special materials such as A286 and products with limited manufacturers or a small supplier base may take a year or more to procure. Contact us for real-time availability.


24. Can I buy Mil-Spec fasteners in small quantities?

Yes! We cater to both small-batch buyers and large production runs. Minimum order quantities may vary by part, and some inexpensive parts may only be purchased in box quantities.


25. What industries use Mil-Spec fasteners?

MIL-STD hardware is widely used in the manufacture of Aerospace, Defense and Military Equipment. Typical applications include aircraft, machines, weapons, instruments, and systems manufactured for the Department of Defense (DOD). Some common uses include:

  • Aircraft
  • Drones
  • Land Vehicles
  • Satellites
  • Ships
  • Submarines
  • Weapon Systems


26. What finishes or platings are available for Mil-Spec fasteners?

Common finishes/platings include:

  • Black oxide
  • Cadmium
  • Passivated stainless steel
  • Zinc


27. What happens if a Mil-Spec fastener fails inspection?

Failed parts should be quarantined and reported immediately. If supplied by MF Supply, we will issue an RMA and provide replacements or refund per our quality and compliance guarantee.


We hope you found this resource/guide about Mil-Spec Fasteners helpful. If you have further inquiries or wish to speak with a representative, please send us an RFQ or contact us directly via phone at (888) 972-7397 / (973) 777-5411 or via email at [email protected]. "Finding the right screw for you" is our commitment to you!