Mil-Spec Socket Cap Screws: A Complete Buyer’s Guide

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. 

Why Buy DFARS-Compliant Mil-Spec Socket Fasteners From MF Supply vs. a National Distributor? 

MF Supply (CAGE Code 58QG4) is built for buyers who need more than a box of screws. We help confirm that the socket fasteners customers need meet the required Mil-Spec, material, finish, DFARS, domestic-source, certification, and traceability requirements before the order ships. For qualifying in-stock orders, MF Supply can provide same-day shipment and supporting documentation, subject to order timing and document availability. 

When sourcing DFARS-compliant socket fasteners, including mil-spec socket head cap screws, product availability is only part of the requirement. Buyers must also confirm material compliance, documentation, traceability, and delivery timing. MF Supply specializes in Mil-Spec and compliance-driven fastener sourcing, helping aerospace, defense, government, and precision manufacturers obtain the correct parts with the required paperwork. 

Unlike a general industrial distributor, MF Supply reviews the buyer’s complete requirements, including the applicable military specification, material, finish, country-of-origin restrictions, certification requirements, and traceability level.  

Why Documentation Matters When Buying Mil-Spec Socket Head Cap Screws

A part number alone does not establish that a socket head cap screw satisfies a defense, aerospace, or government procurement requirement. Buyers may also need to verify the manufacturer, material melt source, country of origin, applicable specification revision, heat or lot identification, finish, testing, and supply-chain traceability.

MF Supply reviews certification requirements during the quotation and order-entry process so the correct documentation can be sourced with the product. Depending on the part, source, and customer requirement, the documentation package may include:

• MF Supply Certificate of Conformance
• Manufacturer Certificate of Conformance {COC}
• DFARS specialty-metals compliance statement
• Lot or heat traceability
• Manufacturer identity and CAGE code, when available
• Country-of-origin documentation
• Material Test Reports including physical and chemical testing results
• Heat-treatment or plating certifications
• Dimensional or inspection reports
• Additional quality records required by the purchase order
• First Article when applicable

Important: Not every document is automatically available with every part. Required certifications and traceability must be identified before the order is placed, particularly when full manufacturer traceability, material reports, or special inspection records are required.

How Does MF Supply’s DFARS Documentation Process Compare With a Generic Industrial Distributor?

MF Supply treats compliance and documentation as part of the sourcing requirement, not as paperwork to chase after the parts have shipped. During quotation, we review whether the customer requires DFARS-compliant material, domestic manufacturing, Buy American compliance, manufacturer traceability, a Certificate of Conformance, or other quality records.

A general catalog distributor may be an excellent source for standard commercial hardware, but buyers should not assume that a listed alloy, country of origin, or product description automatically satisfies DFARS requirements or other certification needs. For regulated or mission-critical applications, the documentation package should be confirmed before the purchase order is accepted.

Documentation & Compliance Comparison

What Does “DFARS-Compliant” Mean for Socket Head Cap Screws? 

DFARS compliance generally means that the fastener satisfies the applicable Department of Defense sourcing and material requirements included in the customer’s contract or purchase order. For specialty-metal fasteners, this may include restrictions on where the metal was melted or produced, subject to the applicable DFARS clause and any available exceptions. 

A supplier should not declare a socket head cap screw DFARS compliant based only on the fact that it is made from alloy steel or stainless steel. Compliance must be supported by the product’s source, material records, certifications, and the specific requirements flowed down on the order

Does MF Supply Offer Same-Day Shipping With Full DFARS Certification?

MF Supply offers same-day shipping on qualifying in-stock socket head cap screw orders received before 3PM. A Certificate of Conformance and available compliance documents can be provided according to the requirements confirmed during quotation. Manufacturer’s Certificate of Conformance paperwork is included with all in-stock Mil-Spec socket fastener orders

For sourced fasteners, the exact documentation package depends on the manufacturer, inventory source, lot, and customer requirements. Buyers needing full manufacturer traceability, Material Test Reports, DFARS certification, or special inspection documents should specify those requirements before placing the order.

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.

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