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Home / Connectors and Fasteners / Hardened Grade 12.9 Socket Head Cap Screw, Black Oxide Finish, Knurled, Sizes M3-M8 Extended Length

Attributes

Brand -
Category Industrial Small Parts / Connectors and Fasteners
Origin -
Material Alloy Steel
Strength Grade 12.9
Surface Finish Black Oxide
Head Type Socket Cap Head
Drive Type Hex Socket (Inner Hex)
Thread Standard Metric Coarse
Available Sizes M3, M4, M5, M6, M8
Hardness HRC 39-44
Special Feature Knurled Under Head
Manufacturing Standard DIN 912 / ISO 4762

5 reviews

A

Anonymous

Apr 24, 2026

Rating: 5/5

Excellent strength for machinery

Used these 12.9 grade screws for a custom engine mount. The hardness is genuine and they did not strip under high torque. The black oxide finish looks professional too.

A

Anonymous

Mar 24, 2026

Rating: 4/5

Good value bulk pack

Great quality for the price. Only giving 4 stars because the hex key needed was not included, but the bolts themselves are top notch hardened steel.

A

Anonymous

Mar 14, 2026

Rating: 5/5

Perfect fit for M5 projects

Ordered the M5 size for my 3D printer frame. The threads are clean and the knurled head helps prevent loosening due to vibration. Highly recommended.

A

Anonymous

Feb 16, 2026

Rating: 5/5

Exactly as described

Needed extended length bolts for a thick assembly. These reinforced bolts handled the load without bending. Fast shipping and well packaged.

A

Anonymous

Feb 14, 2026

Rating: 5/5

High quality finish

The black oxide coating is even and provides decent corrosion resistance for indoor use. The cup head sits flush as expected. Will buy again.

5 FAQ

Q: Are these screws rust-proof for outdoor use?

A: The black oxide finish provides mild corrosion resistance. For harsh outdoor environments, we recommend applying additional grease or using stainless steel alternatives.

Q: Do you offer bulk discounts for over 1000 units?

A: Yes, we offer tiered pricing for bulk orders. Please contact our sales team directly through the store page for a custom quote.

Q: What is the recommended torque for the M6 size?

A: For Grade 12.9 M6 bolts, the typical torque specification is around 10-12 Nm, but please consult a torque chart for your specific application and lubrication conditions.

Q: Can these be used with aluminum parts?

A: Yes, but be cautious of galvanic corrosion between steel and aluminum. Using an anti-seize compound is advised to prevent seizing and corrosion.

Q: Is the thread length full or partial?

A: These are fully threaded bolts across all available sizes (M3 to M8), ensuring maximum grip length for your assembly.

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