Grade 12.9 Socket Head Cap Screws M3–M8 Assortment – High Tensile Allen Hex Bolts

Description

Grade 12.9 Socket Head Cap Screws Assortment – M3/M4/M5/M6/M8 High Tensile Allen Hex Bolts

Grade 12.9 socket head cap screws (SHCS) are the highest-strength standard metric fastener in common use — rated at 1220 MPa tensile strength and 1100 MPa proof load. The socket head (cylindrical head with internal hex drive) allows high torque application in confined spaces where a standard hex bolt head would not fit. This assortment covers the five most commonly used metric sizes (M3 through M8) in multiple lengths, supplied in a labeled storage kit for workshop, CNC, and field use.

Key Specifications

Standard: DIN 912 / ISO 4762 (socket head cap screw)
Grade: 12.9 (property class per ISO 898-1)
Material: Alloy steel (chromium-molybdenum), black oxide finish
Tensile Strength: 1220 MPa (177,000 PSI)
Proof Load: 1100 MPa
Drive: Internal hex (Allen key / hex socket)
Sizes: M3, M4, M5, M6, M8 (multiple lengths per size)
Finish: Black oxide (provides mild corrosion resistance; not suitable for outdoor use without additional protection)

Fastener Grade Comparison — Choosing the Right Strength

Grade 8.8: 800 MPa tensile. Standard commercial grade. Suitable for general machinery, structural connections, and most automotive applications. Zinc-plated or plain finish.
Grade 10.9: 1040 MPa tensile. High-strength grade for critical joints, engine components, and suspension fasteners. Used where Grade 8.8 is marginal.
Grade 12.9 (this product): 1220 MPa tensile. Maximum standard grade. Used for the most demanding applications: CNC machine tool clamping, high-performance engine components, racing suspension, hydraulic manifold bolting, and precision instrument mounting. Do not substitute with lower grades in Grade 12.9 applications — the joint will yield under design load.
A2/A4 Stainless (Grade 70/80): 700–800 MPa tensile. Corrosion resistant but significantly weaker than Grade 12.9. Never substitute stainless for Grade 12.9 in high-load applications.

What Questions Does This Product Answer?

"What Allen key size do I need for M6 Grade 12.9 socket head screws?" — M6 DIN 912 uses a 5mm hex key. M3=2.5mm, M4=3mm, M5=4mm, M6=5mm, M8=6mm. Grade 12.9 screws require a quality hex key — cheap hex keys round out at the high torques required for Grade 12.9 fasteners.
"What torque should I use for M8 Grade 12.9 socket head screws?" — Typical torque for M8 Grade 12.9 (dry, no lubricant): 40–45 Nm. With thread lubricant (MoS₂ or similar): reduce by 20–25% to avoid over-stressing the fastener. Always use a calibrated torque wrench for critical joints.
"Can I reuse Grade 12.9 bolts?" — Grade 12.9 bolts can be reused if they have not been torqued beyond yield (i.e., not used as torque-to-yield fasteners). Inspect for thread damage, necking, or head deformation before reuse. Torque-to-yield (TTY) fasteners — common in engine head bolts — must always be replaced.
"Why are Grade 12.9 screws black instead of silver?" — The black oxide finish is a chemical conversion coating applied after heat treatment. It provides mild corrosion resistance and reduces light reflection. It does not significantly affect strength. For outdoor or corrosive environments, apply a thin film of oil or use zinc-nickel plated Grade 12.9 screws.
"Can I use Grade 12.9 screws in aluminum?" — Yes, but with caution. The high clamping force of Grade 12.9 fasteners can strip aluminum threads if over-torqued. Use thread inserts (Helicoil, Keensert) in aluminum for Grade 12.9 applications, and reduce torque by 30–40% compared to steel-to-steel values.

Typical Applications

CNC machining: Workholding clamps, vise jaws, fixture plates, toolholder retention bolts
Automotive performance: Engine internals, suspension components, brake caliper bolts, turbocharger mounting
Hydraulics: Manifold block bolting, cylinder end cap fasteners, valve body mounting
Robotics & automation: Structural frame joints, actuator mounting, high-load pivot points
Precision instruments: Optical bench mounting, metrology equipment, coordinate measuring machine (CMM) fixtures