UNC 4-40 6-32 8-32 10-32 Grade 10.9 Flat Head Allen Bolts

UNC Black Grade 10.9 Countersunk Hex Socket Screws — 4-40, 6-32, 8-32, 10-32

Upgrade your builds with these precision-engineered US Standard (UNC) countersunk hex socket screws. Made from high-strength Grade 10.9 alloy/carbon steel with a sleek black finish, these flat-head Allen bolts deliver a flush, professional look for mechanical assemblies, electronics enclosures, DIY projects, and more.

Key Specifications

• Standard: UNC (US Standard) Machine Screws
• Grade: 10.9 High-Strength Carbon / Alloy Steel
• Finish: Black oxide coating for corrosion resistance and a clean aesthetic
• Drive Style: Hex Socket (Allen / Internal Hex)
• Head Style: Countersunk (Flat Head) — sits flush with the surface
• Available Thread Sizes:
  • 4-40 (diameter: 0.112 in)
  • 6-32 (diameter: 0.138 in)
  • 8-32 (diameter: 0.164 in)
  • 10-32 (diameter: 0.190 in)
• Size Example: 8#-32 × 1/2" = thread diameter 0.164 in, 32 threads per inch, 1/2 in thread length
• Material: Alloy / Carbon Steel

Note: Dimensions are hand-measured per batch and may have a minor tolerance variance. Please verify your required size before ordering.

Made in Mainland China.

Why Choose These Screws?

• ✅ Flush Finish: Countersunk flat head sits perfectly level with your workpiece for a clean, professional result
• ✅ High Strength: Grade 10.9 construction handles demanding mechanical and structural applications
• ✅ Versatile Sizing: Four UNC thread sizes in one listing — ideal for mixed-project toolboxes
• ✅ Easy Installation: Hex socket drive prevents cam-out and allows precise torque control with any standard Allen wrench or hex key set
• ✅ Black Oxide Coating: Adds a layer of corrosion resistance while giving hardware a refined, stealthy appearance

Common Applications

• Electronics enclosures and computer cases
• Robotics and CNC machine assemblies
• Furniture and fixture hardware
• Automotive and motorcycle accessories
• DIY and maker projects

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Frequently Asked Questions

Q: What is the difference between 4-40, 6-32, 8-32, and 10-32 UNC screws?

A: These designations refer to the thread diameter and threads per inch (TPI). For example, 8-32 means 0.164 inch diameter with 32 threads per inch. A larger first number means a larger diameter screw, while the second number indicates how fine or coarse the thread pitch is.

Q: What Allen wrench / hex key size do I need for these screws?

A: The required hex key size varies by screw diameter. Typically, 4-40 uses a 3/32" hex key, 6-32 uses a 7/64", 8-32 uses a 9/64", and 10-32 uses a 5/32" hex key. Always verify with your specific fastener before installation.

Q: Are these screws suitable for outdoor use?

A: The black oxide coating provides moderate corrosion resistance, making these screws suitable for indoor mechanical applications and low-moisture environments. For prolonged outdoor or high-humidity exposure, consider applying a protective coating or using stainless steel alternatives.

Q: Can I use these screws in aluminum or plastic housings?

A: Yes. These Grade 10.9 countersunk screws are widely used in aluminum enclosures, plastic panels, and electronics chassis. Ensure the receiving material has the correct tapped hole or insert for the UNC thread size you select.

Production & Packaging Notice

To maintain high stock availability and fast shipping times, our items are sourced from multiple verified manufacturing facilities. While the core quality, materials, and product specifications remain identical, you may notice slight variations in the packaging design, manufacturing origin, or the wording of the printed instructions.