Welcome to the second edition of our “What the heck is that” series, where we discuss some of the unique fasteners and electronic hardware that manufacturers use in the design and assembly of their products. If you sell to the military either directly or indirectly, then you are probably aware of today’s topic: “DFARS” and “Mil-spec fasteners”.
What does Mil-spec mean anyway?
Before we get into the nitty gritty of DFARS, let’s discuss what makes a “Mil-spec” fastener. Mil-spec is the informal name for the military standard the U.S. Department of Defense uses in the production of military equipment. For example, the MS24693C pictured above is a fastener produced according to military standards.
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 and suppliers who 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 Distributors [QSLD] and the Qualified Suppliers List for Manufacturer’s [QSLM].
AKA – Also known as…..
Mil-spec fasteners are usually designated by an AN, MS, NAS or NASM prefix followed by a part number. Each of these prefixes is an abbreviation: NAS stands for National Aerospace Standard and MS stands for Military Standard. An example of one of the most common and popular Mil-spec machine screws is the MS24693C. Its commercial equivalent is a Phillips Flat 100 degree Machine Screw in 300 series stainless steel. Below, we’ll tell you more about this popular fellow.
Who uses Mil-spec Fasteners?
Mil-spec fasteners are used by anyone manufacturing or servicing military equipment. Often, the bill of materials calls for specific Mil-spec grade fasteners in accordance with a part number, drawing or procurement requirement. Some of the most common uses of Mil-spec fasteners include aerospace and naval vessels.
Now, tell me 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 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
An example of a DFARS Mil-Spec Screw please!
As we’ve learned, the MS24693C is actually Phillips Flat 100 degree Machine screws in 300 series stainless steel. The MS24693-C4 is a 4-40 x 3/8 Phillips Flat 100 Degree Machine Screw in 302 Stainless Steel, and it is one of the most widely used sizes. Interestingly, the MS24693C superseded the AN662C series, so you might come across the AN662C on an older print of bill of materials. Keep in mind, with any design or manufacturing decision, the reason for using a specific screw generally rests in the hands of engineering.
Features of the MS24693C
– Strict military standards ensure performance and reliability
– Made/melted in the USA or other DFARs-approved country
– Materials and dimensions meet Federal standard FF-S-92
– Inspected 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
Lessons Learned: Considerations when purchasing MS24693C or other Mil-spec DFARs fasteners
- Always ask for “full certifications”. This includes part name, part description, date of manufacture, lot number, chemical composition of material, and treatment of material including plating or passivation.
- At point of purchase, make sure the screws are DFARS. If you do not specifically ask for DFARS-compliant screws, you might receive screws that don’t meet the DFARS requirements, in which case, they won’t meet military standards. We’ve learned this the hard way so hopefully you don’t have to!