Buyer’s Guide to Mil-Spec Fasteners

7 things you need to know

If you sell to the military either directly or indirectly, then you are probably familiar with Mil-spec fasteners. But, what exactly are they and what should you know before buying them? We’d like to help you out with this Seven point buyer’s guide.

1. What does Mil-spec mean anyway?

Mil-spec or MIL-STD, is the informal name for the military standard the U.S. Department of Defense uses in the production of military equipment. Critical fasteners and components used in the production, repair and maintenance of this equipment are classified as “Mil-spec” fasteners. These parts are usually designated by an AN, MS, NAS or NASM prefix followed by a part number (i.e. MS24693C-4). Each of these prefixes is an abbreviation: for example: NAS stands for National Aerospace Standard and MS stands for Military Standard.

2. What’s the difference between Mil-spec and commercial fasteners?

Mil-spec fasteners look a lot like their civilian cousins, but these little guys are made to a specific standard that defines in detail, the screw’s attributes, including: dimensions, tensile strength, hardness, threads, drive type, material qualities and plating, just to name a few. Mil-spec fasteners are even traceable by lot to designated manufacturers. The government maintains a list of factories that are qualified to manufacture and distribute Mil-spec fasteners. These suppliers have met all the government’s requirements and pass the highest quality control standards. This designation is called Qualified Suppliers List for Manufacturer’s [QSLM]. Commercial fasteners are not held to such specific and exacting standards.

3. Who uses Mil-Spec Fasteners?

Mil-spec fasteners are used by anyone manufacturing or servicing military equipment. How do you know if your project requires Mil-spec parts? Often, the bill of materials (BOM) calls for specific Mil-spec grade fasteners in accordance with a part number, drawing, NIIN or NSN or procurement requirement. Some of the most common uses of Mil-spec fasteners include aerospace and naval vessels.

4. Do Mil-Spec fasteners have different features and standards than commercial fasteners?

Mil-spec parts are manufactured and tested to strict military standards ensure performance and reliability. In general, commercial fasteners will not have the same exacting quality standards. Let’s look at a specific example and compare the Mil-Spec MS24693-C4, which is a 4-40 x 3/8 Phillips Flat 100 degree Machine screws in 300 series stainless steel, to its commercial cousin.

Features of the MS24693C-4:

• ­  Manufactured in an 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 standard
• ­   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 and chemical and physical certification
• ­  Available in diameters from #0 through 1/4 inch in coarse and fine thread and various lengths

Features of a 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 to 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 are not.

5.   What level of certification is required?

Generally, a Certificate of Conformance (COC) or a record affirming a fastener has met the requirements of the relevant specification, contract or regulation is sufficient for Mil-Spec fasteners. Full certifications, which include the part name, part description, date of manufacture, lot number, chemical composition of material, and treatment of material including plating or passivation, and material test reports, are often available for a fee. It is critical to ask for the level of certification (COC, full material certs, passivation certs, etc) in advance in order to have the most efficient buying experience.

6. Are there other factors to consider when procuring Mil-spec fasteners?

Great question! 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 include: 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.

Important Note: 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.

To keep up to date with DFARs requirements, visit www.acq.osd.mil/dpap/dars/dfarspgi/current/index.html

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

The Defense Logistics agency is a great resource. They maintain a comprehensive database of specifications and drawings. They also maintain a catalog of hardware that includes NIINs and NSNs that sometimes called out in a bill of materials. Check out the following links for more comprehensive information regarding hardware:

http://www.dla.mil/TroopSupport/IndustrialHardware/  – to view catalogs of mil-spec parts and specs by category

http://quicksearch.dla.mil/qsSearch.aspx   – To look up a specific part

http://www.mfsupply.com/mil-spec-fasteners-s/1823.htm – To see MF Supply’s Mil-Spec fastener stock

http://www.mfsupply.com/v/vspfiles/assets/images/MFSUPPLY_MILITARY.pdf – To download MF Supply’s Mil-spec line card

For more detailed information about Mil-Spec parts, to request a Mil-Spec Line Card or to send an RFQ, visit our website. And if you don’t see what you need listed, as always, ask us. “Finding the right screw for you” is our tag line after all!

Contact me at robin@mfsupply.com with your questions, comments or helpful hints!