Variations of Mil-Spec Socket Cap ScrewsMil-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 MS24671and 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. Why Buy Mil-Spec Socket Head Cap Screws From MF Supply? At MF Supply, we stock and source a broad catalog of Mil-Spec socket head cap screws including:
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!
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