Mil-Spec Socket Cap Screws: A Complete Buyer’s Guide
Posted: September 22, 2025 Filed under: Mil-Spec, Mil-Spec Fasteners, MS16995, MS16996, MS16997, MS16998, MS24671, NAS1351, NAS1352, Socket Head Cap Screw | Tags: Fasteners, Guide, Mil-spec fasteners, Mil-Spec Fasteners Distributor, Mil-Spec Fasteners Supplier, Mil-Spec Socket Head Cap Screws, Military Fasteners, Military Fasteners Supplier, MS16995, MS16996, MS16997, MS16998, MS24671, NAS1351, NAS1352, Socket Cap Screws Leave a comment
When it comes to aerospace, defense, and mission-critical industrial applications, not all socket cap screws are created equal. While commercial socket cap screws can be sufficient for general manufacturing, Mil-Spec socket cap screws are engineered, tested, and certified to meet the stringent requirements of the U.S. military and defense supply chain.
In this guide, we’ll cover:
- The variations of Mil-Spec socket cap screws
- Materials, platings, and optional features
- The part number taxonomy (MS, NAS, NASM, AN designations)
- How Mil-Spec differs from commercial socket caps
- Typical applications and industries
- MF Supply’s Mil-Spec socket cap screw catalog offerings
Variations of Mil-Spec Socket Cap Screws
Mil-Spec socket cap screws (sometimes called MS or NAS socket head cap screws) come in multiple variations to meet specific performance requirements: The 2 main Mil-Spec standards are:
- Standard socket head cap screws – Cylindrical head, hexagonal drive. Designed for high-strength fastening where space is limited.
- Flat socket cap screws – Used in clearance-sensitive applications where flush mounting is critical.
Note: Low Head and Button Head socket cap screws do not have a Mil-Spec equivalent.
Mil-Spec socket head cap screws come in several varieties, including:
- Drilled heads (safety wire holes) – Feature cross-drilled holes in the head to allow safety wiring, preventing loosening in high-vibration environments like aircraft engines.
- Thread-locking (pre-applied patch) – Includes a nylon or chemical locking element on the threads, providing resistance to vibration loosening.
- Vent/drilled-through screws – Designed to eliminate trapped gas or contamination in vacuum or cleanroom environments.
Note: Varieties including threadlocking, drilled heads and vented options are less common and may only be available per special order with minimums and lead times.
Materials & Platings
Mil-Spec socket cap screws are offered in specific materials and platings with mechanical properties that meet or exceed ASTM/SAE standards. Common options include:
- Alloy Steel – High tensile strength, black oxide or cadmium plated for corrosion resistance
- CRES Stainless Steel (18-8/300 series stainless steel) – Corrosion resistance, often used in aerospace and marine environments
- CRES A286 Stainless Steel superalloy – Extreme temperature resistance, high strength and with excellent corrosion & oxidation resistance
Note: SS316 stainless steel is less common and may only be available by special order with minimums and lead times.
Platings and Coatings:
- Black Oxide (MIL-C-13924, Class 1) – Standard corrosion resistance
- Cadmium Plating (QQ-P-416) – Excellent corrosion resistance and lubricity. Widely specified in legacy Mil-Spec standards.
- Passivation (for stainless steels, QQ-P-35) – Removes surface contaminants and improves corrosion resistance.
Part Number Taxonomy
Military grade fasteners or “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.
The Defense Supply Center Philadelphia (DSCP), part of the DLA (Defense Logistics Agency), has a Qualified Suppliers List for Manufacturers (QSLM) identifying pre-qualified sources for certain products purchased by DSCP. Referred to also as the QPL (Qualified Products List), manufacturers on this list are recognized by DSCP as meeting all necessary criteria, particularly regarding quality control and paperwork.
Each part number defines key parameters: head style, material, finish, thread class, and whether features like drilled heads or locking elements are included.
The main core part numbers identifying standard Mil-Spec socket head cap screws are MS16995, MS16996, MS16997, MS16998, NAS1351, and NAS1352. Flat head socket head cap screws fall under parts MS24671 and MS24672.
- MS (Military Standard) – Legacy part numbers (e.g., MS16995), still widely used in aerospace and defense
- NAS (National Aerospace Standards) – High-performance standards developed for aerospace (e.g., NAS1351, NAS1352)
- NASM – Updated versions of NAS standards under SAE governance
- AN (Army-Navy) – Older standards, often superseded by MS or NAS numbers
The base part is followed by a Material Code:
- “-” = Alloy Steel
- “C” = Corrosion Resistance Steel (18-8 stainless steel)
- “N” = Heat-Resistant Steel (A286)
- Let’s further break down a common Mil-Spec socket cap:
- For example: NAS1352N028, sometimes written as NAS1352N02-8
- 2-56 X 1/2 Mil-Spec Socket Head Cap Screw A286 Stainless Steel DFAR
- NAS1352 = Coarse thread Socket Head cap screw
- N = Heat-Resistant Steel (A286)
- 02 = 2-56 Diameter
- 8 = .500 or 1/2 screw length
Note: The Aerospace Industries Association maintains an updated list of NAS parts available to members and/or for purchase.
Why Mil-Spec Socket Caps Are Different from Commercial
Commercial socket caps may look identical to Mil-Spec socket caps. However, commercial fasteners may lack the controlled processes, documentation, and certifications required for military or aerospace projects.
Differences between Mil-Spec and commercial socket head cap screws may include:
1. Certification & Paperwork
Available Paperwork may include:
- Manufacturer’s Certificate of Conformance (C of C)
- Lot and heat traceability
- Dimensional testing
- Material Test Reports (MTRs)
- DFARS compliance certification for defense projects
2. Testing
Mil-Spec socket caps undergo rigorous mechanical, dimensional, and sometimes nondestructive testing to verify hardness, tensile strength, shear strength, plating thickness, and more.
3. Authorized Manufacturers
Manufacturers listed on the QPL (Qualified Products List), the Qualified Suppliers List for Manufacturers (QSLM), or those approved under aerospace quality systems (AS9100, NADCAP for plating, etc.) are authorized to produce Mil-Spec socket caps. This ensures supply chain integrity and reliability in defense applications.
Applications
Mil-Spec socket head cap screws are commonly used in:
- Aerospace & Defense – Aircraft structures, engines, avionics, and ground support equipment
- Military Vehicles & Marine – Tanks, ships, submarines, and defense electronics
Other industries use Mil-Spec fasteners because of their quality and traceability. Two examples include Precision Manufacturing where vibration, temperature extremes, or strict compliance require certified fasteners, and Medical & High-Tech Industries where cleanrooms, vacuums, or corrosive environments require traceability is essential.
MF Supply’s Mil-Spec Socket Cap Offerings
At MF Supply, we stock and source a broad catalog of Mil-Spec socket head cap screws including:
- NAS1351 & NAS1352
- MS16995, MS16996, MS16997, MS16998
- MS24671 & MS24672
- Variants with drilled heads, vent holes, and locking elements
- Multiple materials, platings, and DFARS-compliant options
We partner with only qualified U.S. and global manufacturers and provide full certification packages upon request.
Beyond strength and performance, the real differentiators are the certifications, testing, and compliance requirements that ensure supply chain integrity.
MF Supply has over 50 years of experience supplying Mil-Spec, DFARS-compliant, and certified hardware. Whether you need a handful of parts or long-term stocking solutions, we’re Your Purchasing Department’s Secret Weapon.
👉 Explore Our Catalog of Mil-Spec Socket Cap Screws or Request a Quote today.
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.
Your Purchasing Department’s Secret Weapon!
Here are 5 reasons to buy from MF Supply
- We Source and Deliver What Others Can’t, Faster Than You Imagined – With speedy solutions for elusive parts and lengthy delivery times – We’ve got you covered with both custom-made specials (send us your prints!) and hard-to-source options, quickly and at a fair price.
- Cost-Effective Functional Equivalents to OEM Brand Fasteners-Why Pay More? – Reduce lead times and costs with the same quality and same performance. Try us for alternatives to brands like McMaster-Carr, MSC, Misumi, PEM, and RAF and experience unmatched savings! Same form, fit and function for less.
- Huge Selection of Certified and Commercial Hardware with Same-day Shipping Available for Countless Items – We source and stock standards, specials, commercial, Mil-Spec & OEM brands in inch and metric sizes. Standards include AN, NAS, MS, IFI, ASTM, ASME, DIN, ISO, JIS. We are sourcing experts for inserts, certified Mil-Spec parts and anything in stainless steel. Many parts are available with manufacturers’ certifications, including DFAR, ROHS and CoC. Trust us to ship on-time from our national distribution centers.
- A User-Friendly, 24/7 Online Shopping Experience – Enjoy a 24/7 online shopping experience with easy-to-use filters, detailed product information, and a constantly updated technical directory. Sign up now for a seamless experience!
- WBE/WOSB Certified Woman-Owned Small Business – As a certified Woman-Owned Small Business, we support your diversity goals. Trust us to meet your fastener and sourcing needs with expertise and efficiency [Cage Code 58QG4].
Newsletter – January / February 2016
Posted: February 11, 2016 Filed under: DFARS, MS16995, MS16996, NAS1351, NJMEP, SBA Emerging Leaders, Socket Head Cap Screw, Uncategorized | Tags: MS16995, MS16996, NAS1351, NAS1352, Socket Head Cap Screw Leave a comment|
Newsletter Volume 18 February 12, 2016 January / February News
Greetings and Happy February! We started 2016 fast out of the gate and are ramping up for a strong Q1, despite a PMI index of 48.2%, reports of contraction in the manufacturing sector and the volatility that sometimes occurs during election years. I hope you are experiencing growth!
Today, I am continuing our discussion on thought leadership within the American Manufacturing community. Additionally, I am glad to get back to our “What the Heck Is that” roots and put the spotlight on one of our best-selling products, the Socket Head Cap Screw.
INSIDE THIS ISSUE
1. SBA EMERGING LEADERS
2. WHAT THE HECK IS A SOCKET HEAD CAP SCREW?
3. MANUFACTURING ROUNDTABLE AND THE NJMEP
4. MF SUPPLY JOINS DPA
5. GOING LEAN?
Since graduating on October 27, I have been introduced to many amazing resources. One exciting development I wanted to share with you is that MF Supply was selected as a case study class for Rutgers Business School. What does that mean, you ask? Well, between now and April 20th, a group of smart and creative Rutgers MBA candidates are analyzing MF Supply and our marketplace. They will use BIG DATA and other tools, and present recommendations including an ROI on where we should focus our energies to grow. One of their initial thoughts was that MF Supply should be targeting companies with Set-Aside needs or Diverse buying initiatives. If you hadn’t heard, MF Supply is a WBE and WOSB certified business, which means if your customer has Set Aside needs, we should be talking! I am so excited for this project and am thankful to the SBA for connecting me to Rutgers and other resources.
If you are curious to know more about the SBA-EL program (in NJ or your state), or think you or someone you know might benefit from participating, please check out these two articles about the program inNJBIZ and American Entrepreneurship Today to find out more. To apply, please email Dominick.Belfiore@sba.gov and tell him I sent you!
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 Socket Head Cap Screws or socket caps, which are sometimes referred to by their trademarked name “Allen” screws, have become the standard among high strength fasteners needed to withstand the faster speeds and higher pressure of today’s machines, instruments and assemblies. They are externally threaded, with a cylindrical head with a flat chamfered top, and a hexagonal recess for internal wrenching.
Who uses Socket Head Cap Screws?
Because of their cylindrical shaped heads and internal wrenching installation method, socket cap screws need less space than alternative fasteners. This makes socket caps ideal for precision assembly work with close tolerances and applications that need a well tooled appearance.
Common uses include machine parts, die fixtures and assemblies.
Why use a Socket Cap vs a Hex Head Cap Screw?
We don’t want to play favorites, but here are a few advantages of using socket caps:
Size matters– The smaller socket head enables driving where there is not sufficient space for wrenches or sockets. In addition, Socket caps are available off the shelf starting as small as 0-80 diameter and are commonly available to diameter 1-1/2-6. Hex Head Cap screws start at 1/4-20 diameter.
Strength – Alloy Steel Socket Caps, though not measured in grades, provide greater tensile strength than equivalent size Grade 5 or Grade 8 steel Hex Head Cap screws. i.e. 1/4-20 Socket cap=180k psi min, 1/4-20 Hex Head Grade 5 =120k psi min, 1/4-20 Hex Head Grade 8 =150k psi min.
Torque – The 6 flat surfaces within the recess allow for high torquing without damaging the head, and with no side clearance restrictions or additional wrench space.
Thread fit- Socket products generally have a 3A thread fit. 3A threads have restrictive tolerances often used where safety is a critical design consideration. Hex Head Cap Screws are generally class 2A. 2A threads offer a combination of performance, economy, and convenience. Nearly 90% of all commercial and industrial fasteners have a 2A fit.
Economy – Socket Cap heads are smaller, hence, the size of the component parts can be reduced, reducing material costs. Smaller parts cost less to drill and tap, take less energy to drive, and weigh less than alternatives.
What options are available?
The most common variables are the head style, diameter and thread, length, material and plating or finish. Socket caps can also be captivated, vented, patched or pelleted. Below are some of the most common options:
HEAD STYLES
There are 4 main available head styles, and each serves a slightly different purpose. All commercial Socket Caps conform to ASME B18.3.
Standard Head – the standard in Socket Head Cap Screws (ASTM A574, F835, DIN912)
Low Head – Use in parts too thin for standard height heads and where clearance is limited (DIN7984)
Flat Head – Countersunk heads at 82 degrees provide maximum flushness and side wall contact (ASTM F835, F879, DIN7991)
Button Head – For use in materials too thin to countersink (ASTM F835, F879, DIN7380)
DRIVES
The most common and readily available drive style is a hexagonal socket drive, however, Socket Caps may also be available in security pin-in-hex, pin-in-torx, or six-lobe torx versions in certain sizes and materials.
Are there other factors to consider?
Of course! “Steel” Socket Caps off the shelf are alloy steel black oxide through heat treatment and come oiled. If you need greater corrosion resistance or a different look than black, consider stainless steel or zinc plating.
If you are considering zinc plated Socket Caps, proceed with caution! Because of their tight tolerances and 3A fit, zinc plating a Socket Cap will often change the thread fit to a commercial nut fit. If you need a 3A fit, you must specify that on your purchase order so the factory can meet your thread fit needs when creating and plating your screws.
Beyond color and plating, there are always other factors to consider, such as: domestic or import, commercial or mil-spec, with or without sprinkles :). And remember, Socket Head Cap Screws can also show up under their most popular domestic brand names (Holo-krome) and mil-spec number (MS16995, MS16996, NAS1351 and NAS1352). If you have any questions, please reach out and ask!
Socket Head Cap Screws available at MF Supply
Here at MF Supply, we offer:
For more detailed information on Socket Head Cap Screws, visit us at http://www.mfsupply.com/category_s/1869.htm
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MANUFACTURERS ROUNDTABLE – NJMEP
Did you ever get an invitation that piqued your interest, and show up at an event wondering if it would be worth your time? On January 27, I said yes to an NJMEP invitation to a Manufacturers Roundtable, hosted by Bergen Community College. I am so glad I went!
Assemblyman Gary Schaer, along with 30 manufacturers, educators and other advocates discussed ways we can support manufacturing in NJ. Many connections were made, and last week, a group of 10 of the students from Bergen’s current CNC training class visited MF Supply to learn more about the Supply chain. They were a bright, motivated and very impressive group of students. If you are hiring, great! I’d love to connect you to the team at Bergen Community College.
And get yourself on the NJMEP (or if you are outside of NJ, contact your state’s MEP) email list to find out about relevant events and programs that just might be a difference maker for your business.
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On November 1, 2015 we were officially welcomed into the DPA Industrial family. What does this mean for our customers? We can now help you with more product categories and pass along fabulous savings on many more items including:
Please contact me to set up a meeting to see if we can help save you time and money by becoming a single source for more of your industrial needs.
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GOING LEAN
Since our core values include striving for achievement, self improvement and growth, we are exploring Lean certification. Is being Lean one of your initiatives? Check out this inspirational video about how Lean processes lead to immediate improvements in a NYC foodbank. Enjoy the video by clicking here!
Regards,
Robin Lieberman
President
P.S. We are closed on February 15 in observance of President’s Day. Wishing you and yours a happy and healthy long weekend and Valentine’s Day from the entire team here at MF Supply.
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