Grade 12.9 Hex Socket Cap Head Screws M2–M6 — Maximum Strength Allen Drive Machine Bolts
When a standard screw strips under torque, a joint works loose under vibration, or a compact fastener needs to carry a load that lower-grade hardware simply cannot handle — that is when engineers, machinists, and precision builders reach for Grade 12.9 hex socket cap head screws. These are the go-to choice for anyone who needs the highest available strength in a standard metric cap head form factor, from robotics builders to CNC machine assemblers to motorsport fabricators.
Each screw is manufactured from Grade 12.9 alloy steel, the highest property class for metric fasteners, with a minimum tensile strength of approximately 1220 MPa. The cylindrical cap head features a hex socket (Allen) drive recess, compatible with standard metric hex keys. Sizes range from M2 x 4mm (≈5/32") up to M6 x 30mm (≈1-3/16"), covering the most common small-to-medium metric cap screw sizes. Available in packs of 10, 30, 50, or 100 pieces to suit prototyping, small-batch, or production needs.
Typical applications include CNC machine frame assembly and linear rail mounting where Grade 12.9 socket head cap screws provide the clamping force needed to prevent joint slip, robotics and drone builds requiring compact high-strength metric bolts in tight spaces, precision jig and fixture construction where consistent torque and joint integrity are critical, and motorsport and performance equipment assembly where maximum strength-to-size ratio matters.
ℹ️ Compatibility: ISO metric coarse thread (DIN 912 / ISO 4762 form factor) — fits standard metric tapped holes M2, M2.5, M3, M4, M5, M6. Hex key sizes: M2=1.5mm, M2.5=2mm, M3=2.5mm, M4=3mm, M5=4mm, M6=5mm. Not compatible with UNC/UNF inch threads.
✅ Key Features of These Grade 12.9 Hex Socket Cap Head Screws
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💪Grade 12.9 Alloy Steel — Maximum Property Class — With a minimum tensile strength of approximately 1220 MPa, these are the strongest standard metric fasteners available, suitable for high-load mechanical assemblies where lower-grade screws would yield or strip.
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🔩Hex Socket (Allen) Drive — High Torque, Compact Access — The internal hex socket allows high torque application with a standard Allen key, and the cylindrical cap head sits flush against the mating surface — ideal for recessed mounting in precision machinery and tight-clearance assemblies.
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📐Wide Size Range — M2 to M6, 4mm to 30mm — Covers 47 size combinations from M2 x 4mm (≈5/32") to M6 x 30mm (≈1-3/16"), making this a single source for the most common small metric cap screws used in robotics, CNC, and precision fabrication.
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🔧DIN 912 / ISO 4762 Form Factor — Conforms to the internationally recognized standard for cylindrical head hex socket screws, ensuring dimensional compatibility with standard metric tapped holes, counterbores, and tooling across all major engineering applications.
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📦Flexible Pack Quantities — 10 to 100 Pieces — Order 10 pieces for prototyping or repair, 30 or 50 for small-batch builds, or 100 for production runs and workshop stock — with per-unit cost savings at higher quantities.
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⚡Consistent Dimensional Accuracy — Manufactured to tight tolerances for reliable fit in tapped holes and counterbores. Consistent thread pitch and head geometry reduce installation issues and ensure repeatable torque behavior across production assemblies.
📐 Technical Specifications — Hex Socket Cap Head Screws
| Head Type |
Cylindrical Cap Head (Socket Head) |
| Drive Type |
Hex Socket (Allen / Internal Hex) |
| Standard |
DIN 912 / ISO 4762 (metric hex socket head cap screw) |
| Material |
Grade 12.9 Alloy Steel |
| Property Class |
12.9 (minimum tensile strength typically 1220 MPa) |
| Thread Standard |
ISO Metric Coarse (M-series) |
| Diameter Range |
M2, M2.5, M3, M4, M5, M6 |
| Length Range |
4mm (≈5/32") to 30mm (≈1-3/16") — shank length, head not included |
| Available Sizes (Diameter × Length) |
M2: 4/5/6/8/10/12/14/16mm | M2.5: 4/5/6/8/10/12/14/16mm | M3: 4/5/6/8/10/12/16/20mm | M4: 6/8/10/12/16/20/25/30mm | M5: 6/8/10/12/16/20/25/30mm | M6: 8/10/12/16/20/25/30mm |
| Hex Key Sizes |
M2=1.5mm | M2.5=2mm | M3=2.5mm | M4=3mm | M5=4mm | M6=5mm |
| Surface Finish |
See variant options / Contact us to confirm |
| Quantity Options |
10 / 30 / 50 / 100 pieces |
⚠️ Note: Screw length refers to shank length only — the cap head is not included in the measurement. Grade 12.9 fasteners are high-strength alloy steel and are generally not recommended for outdoor or corrosive environments without additional surface protection. For structural or impact-loaded applications, contact us to confirm suitability.
❓ Frequently Asked Questions
How do I choose the right length for a hex socket cap head screw?
The listed length is the shank length only — the head is not included in the measurement. Measure the thickness of the material being clamped and add the required thread engagement depth in the receiving part. As a general rule, aim for at least 1.5× the thread diameter in engagement depth. For example, an M4 x 10mm (approx. 3/8") screw is typically used for panels up to 7–8mm thick with a tapped hole below.
What is the tensile strength of Grade 12.9 screws?
Grade 12.9 is the highest standard property class for metric steel fasteners. These screws typically have a minimum tensile strength of 1220 MPa and a proof load stress of approximately 1100 MPa. This makes them suitable for high-stress mechanical assemblies, precision machinery, and applications where standard Grade 8.8 or 10.9 screws may not provide sufficient clamping force.
Are Grade 12.9 screws suitable for outdoor or corrosive environments?
Grade 12.9 screws are typically made from alloy steel and are generally not recommended for outdoor or corrosive environments without additional surface treatment. They are generally used in dry, indoor mechanical applications. For outdoor or corrosive environments, consider using stainless steel fasteners or applying a corrosion-resistant coating. Contact us if you need guidance on the right fastener for your environment.
What thread standard do these screws use — are they compatible with my tapped holes?
These screws use ISO metric coarse thread (standard M-series pitch). M2, M2.5, M3, M4, M5, and M6 sizes are compatible with standard metric tapped holes and nuts. They are not compatible with UNC/UNF inch-standard threads. Always verify your receiving thread is metric before ordering.
What hex key (Allen wrench) size do I need for each screw diameter?
Hex key sizes for ISO metric cap head screws are standardized: M2 typically uses a 1.5mm hex key, M2.5 uses 2mm, M3 uses 2.5mm, M4 uses 3mm, M5 uses 4mm, and M6 uses 5mm. These are standard DIN 912 / ISO 4762 dimensions. Always use a properly fitting hex key to avoid rounding the socket.
Can I use Grade 12.9 screws with standard nuts and threaded inserts?
Yes. Grade 12.9 screws use standard ISO metric coarse thread and are compatible with standard metric nuts, threaded inserts (e.g., heat-set or press-fit), and tapped holes of the corresponding size. For maximum joint strength, pair with Grade 10 or Grade 12 nuts. Using lower-grade nuts may result in the nut stripping before the screw reaches its rated load.
What is the difference between Grade 12.9 and Grade 8.8 or 10.9 screws?
The property class number indicates the tensile strength and yield ratio of the fastener. Grade 8.8 screws typically have a tensile strength of around 800 MPa, Grade 10.9 around 1040 MPa, and Grade 12.9 around 1220 MPa. Grade 12.9 is used where maximum clamping force is required in a compact fastener size, such as in precision machinery, motorsport, and aerospace-adjacent applications. The trade-off is that Grade 12.9 screws are more brittle than lower grades and should not be used in applications subject to significant impact or shock loading.
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