Socket head cap screws—also known as Allen bolts or hex socket screws—feature a cylindrical head with an internal hex drive. This recess allows torque delivery using an Allen key or hex wrench, making them ideal for installations in confined spaces and precision-critical assemblies. Their clean profile and high-strength capability make them favored in military, aerospace, and industrial equipment.
1. Military & Aerospace Specifications
Socket head cap screws for defense use meet stringent MIL-SPEC standards such as NAS1351C, NAS1352C, MS16995, MS16996, MS16997, and MS16998. These part numbers define attributes including material composition, thread length, head design, and coating, ensuring consistent quality and compatibility across systems.
2. Materials, Strength & Corrosion Resistance
Military-grade socket screws are manufactured from materials such as:
- 300-series stainless steel (e.g. 302 SS): Provides excellent corrosion resistance and is often used in NAS1351C/1352C series parts, typically passivated.
- High-tensile alloy steel: Conforms to MIL-SPEC for MS16997/MS16998, offering tensile strength up to ~160 ksi (~1,100 MPa) and Rockwell hardness around 36–45 HRC. These may have cadmium or chromate finishes.
- A286 stainless or nickel alloys: Used when higher strength or temperature resistance is required.
All sockets undergo full traceability with certification and DFARS compliance.
3. Threads, Torque & Head Design
Standard parts include Class 3A internal thread engagement per NAS/AN/MS standards for preload control and vibration resistance. The hex socket drive improves torque transmission in constrained areas and ensures reliable clamping without marring surrounding surfaces.
Socket Head Cap Screw Comparison Table
| Specification | Material & Features | Typical Uses |
|---|---|---|
| NAS1351C / NAS1352C | 300‑series stainless, fine/coarse thread, passivated finish | Corrosion-critical aerospace assemblies |
| MS16995 / MS16996 | 18‑8 SS or A286 SS, full or partial thread | Structural/avionics installations |
| MS16997 / MS16998 | High-strength alloy steel, cadmium/chromate plating, 160 ksi tensile | Heavy-duty structural or shock-loaded joints |
| Titanium / Ni-alloy Versions | Lightweight, non-magnetic, shear/temperature-resistant | Stealth platforms, naval systems |
| Standard Metric/ANSI ISO Versions | Class 8.8–12.9, metric or inch threads, various head lengths | General industrial and equipment use |
Best Practices & Installation Tips
- Use calibrated hex keys or torque wrenches to achieve proper preload without stripping internal drive.
- Match coating type to environment: stainless or passivated screws for corrosive settings; cadmium or zinc-nickel for strength-critical, high-humidity uses.
- Confirm head dimensions to ensure clearance in recessed or flush-fitting assemblies.
Why This Matters
Socket head cap screws combine strength, precision, and compact form factor. Their internal drive allows secure torque application in tight or recessed spaces. Standards compliance—and verified material and traceability—ensures fasteners meet demanding military and aerospace quality expectations.
Metric Bolt: Your Source for Mission-Critical Socket Head Screws
At Metric Bolt, we supply military-grade socket head cap screws—including NAS1351C, NAS1352C, MS16995–98, titanium and nickel alloy options—each with certified finishes, full traceability, and support documentation.
Need certified socket head screws that meet military or aerospace standards?
Contact Metric Bolt for assistance with part selection, sourcing, or compliance requirements.
