What does Grade 10.9 mean for alloy steel screws?

Grade 10.9 is a metric property class indicating a minimum tensile strength of 1040 MPa (approximately 150,800 psi) and a proof load of 940 MPa. These screws are generally suitable for high-stress mechanical assemblies, automotive components, and structural joints where standard Grade 8.8 fasteners may be insufficient.

Are these screws suitable for outdoor or corrosive environments?

Grade 10.9 alloy steel screws are not inherently corrosion-resistant. For outdoor or humid environments, we recommend applying a corrosion-inhibiting coating or using stainless steel alternatives. If you must use these screws outdoors, a zinc-plated or black-oxide finish typically provides basic short-term protection.

What thread standard do these countersunk screws use?

These screws follow the ISO metric coarse thread standard (DIN 7991 / ISO 10642 profile). M2 through M6 sizes use standard metric pitches: M2 (0.4mm pitch), M2.5 (0.45mm), M3 (0.5mm), M4 (0.7mm), M5 (0.8mm), M6 (1.0mm). They are compatible with standard metric tapped holes and nuts.

What hex key (Allen wrench) size do I need?

The required hex key size varies by thread diameter: 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. Always confirm with a test fit before applying full torque.

M2-M6 Countersunk Socket Head Cap Screws – Grade 10.9 Alloy Steel

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M2-M6 Countersunk Socket Head Cap Screws – Grade 10.9 Alloy Steel

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Thread Diameter x Length: M2 x 3mm

Amount: 10 Pcs

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$6.79 USD

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In stock (500 units), ready to be shipped

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Countersunk Socket Head Cap Screws M2–M6 — Flush-Mount Strength for Precision Work

When a protruding bolt head is not an option — whether you're assembling a CNC enclosure, mounting a circuit board bracket, or building a mechanical linkage — a standard cap screw simply won't do. Engineers, machinists, and serious DIYers who need a clean, flush surface without sacrificing clamping force rely on countersunk socket head cap screws. These M2–M6 countersunk socket head cap screws deliver the torque capacity of a hex-drive fastener with the low-profile seating of a flat-head design, solving both the aesthetic and functional problem in one fastener.

Each set contains your chosen quantity (10, 30, 50, 100, or 500 pieces) of the same size and length. The screws are manufactured from Grade 10.9 alloy steel, which provides a minimum tensile strength of approximately 1040 MPa (≈150,800 psi). Thread diameters span M2 through M6, with lengths ranging from 3mm (≈1/8") to 50mm (≈2"), giving you a broad selection for thin-panel work all the way up to structural fastening. The 90° countersunk head profile conforms to the ISO 10642 / DIN 7991 standard, ensuring compatibility with standard countersunk holes.

Typical use cases include flush-mounting panels in electronics enclosures and server racks, securing linear rail carriages and CNC axis components, assembling aluminum extrusion frames, and replacing stripped or corroded fasteners in machinery and automotive sub-assemblies. The internal hex (Allen) drive resists cam-out under high torque, making these screws a reliable choice for countersunk socket head screw applications where repeated assembly and disassembly is expected.

🔩 Compatibility: ISO metric coarse thread (DIN 7991 / ISO 10642). Fits standard metric tapped holes M2–M6. Requires a metric hex key (Allen wrench): 1.5mm for M2, 2mm for M2.5, 2.5mm for M3, 3mm for M4, 4mm for M5, 5mm for M6.

⚠️ Note: Grade 10.9 alloy steel is not corrosion-resistant. For outdoor or high-humidity environments, apply a protective coating or contact us to confirm suitability for your application.

✅ Key Features of These Countersunk Socket Head Cap Screws

💪Grade 10.9 Alloy Steel Construction — Minimum tensile strength of ~1040 MPa makes these screws suitable for high-load mechanical assemblies, automotive brackets, and structural joints where lower-grade fasteners would yield under stress.
📐90° Flat Countersunk Head Profile — Conforms to ISO 10642 / DIN 7991, allowing the head to sit perfectly flush with the mating surface. Ideal for countersunk socket head screw applications in panels, rails, and enclosures where a protruding head would interfere with clearance or aesthetics.
🔑Internal Hex (Allen) Drive — The socket drive resists cam-out and allows high torque application in tight spaces where a Phillips or slotted driver would slip. Works with standard metric hex keys available at any hardware store.
📏Wide Size Range: M2 to M6, 3mm to 50mm — A single product line covers everything from delicate M2 x 3mm (≈1/8") fasteners for electronics to robust M6 x 50mm (≈2") bolts for structural aluminum extrusion frames, reducing the number of SKUs you need to stock.
📦Flexible Quantity Options — Available in 10, 30, 50, 100, and 500-piece packs. Buy 10 pcs for a quick repair or 500 pcs for production-line restocking — the per-unit cost decreases with larger quantities, making bulk purchasing cost-effective for workshops and small manufacturers.
🏭Consistent Dimensional Accuracy — Thread pitch and head geometry are held to metric standard tolerances, ensuring reliable engagement with tapped holes and countersunk bores machined to ISO specifications. Reduces the risk of cross-threading or misalignment during assembly.

📐 Technical Specifications — Countersunk Socket Head Cap Screws

Product Type	Countersunk (Flat Head) Socket Head Cap Screw
Drive Type	Internal Hex (Allen / Socket)
Head Angle	90°
Standard	ISO 10642 / DIN 7991
Material	Alloy Steel
Grade / Property Class	10.9
Tensile Strength	Min. ~1040 MPa (≈150,800 psi)
Proof Load Stress	~940 MPa
Thread Standard	ISO Metric Coarse
Available Thread Diameters	M2, M2.5, M3, M4, M5, M6
Available Lengths	3mm (≈1/8") – 50mm (≈2") — see variant options
Hex Key Size	M2: 1.5mm \| M2.5: 2mm \| M3: 2.5mm \| M4: 3mm \| M5: 4mm \| M6: 5mm
Finish / Surface Treatment	See variant options
Corrosion Resistance	Not inherently corrosion-resistant — contact us to confirm
Pack Quantities	10 / 30 / 50 / 100 / 500 pieces
Country of Origin	See variant options

❓ Frequently Asked Questions

How do I choose the right length for a countersunk socket head screw?

Measure the total thickness of the material being fastened. For a flush finish, the screw length should equal the material thickness so the head sits level with the surface. For example, a 10mm (3/8") thick panel typically calls for an M3 x 10mm or M4 x 10mm screw. When in doubt, choose the next length up and countersink slightly deeper. If you're threading into a blind hole, leave at least 1–1.5× the thread diameter of clearance at the bottom.

What does Grade 10.9 mean, and how strong are these screws?

Grade 10.9 is a metric property class indicating a minimum tensile strength of approximately 1040 MPa (≈150,800 psi) and a proof load stress of ~940 MPa. In practical terms, these screws are generally stronger than Grade 8.8 fasteners and are suitable for high-stress mechanical assemblies, automotive components, and structural joints. Always verify the required torque spec for your specific thread size and application before installation.

Can I use these screws outdoors or in humid environments?

Grade 10.9 alloy steel is not inherently corrosion-resistant. For outdoor, marine, or high-humidity environments, we recommend applying a corrosion-inhibiting coating (such as zinc plating or a rust-preventive oil) or switching to stainless steel fasteners. If you must use these screws in mildly damp conditions, a black-oxide or zinc-plated finish typically provides basic short-term protection. Contact us to confirm suitability for your specific environment.

What thread standard do these screws follow, and are they compatible with standard metric hardware?

These screws follow the ISO metric coarse thread standard (DIN 7991 / ISO 10642 head profile). Standard metric pitches apply: M2 (0.4mm pitch), M2.5 (0.45mm), M3 (0.5mm), M4 (0.7mm), M5 (0.8mm), M6 (1.0mm). They are compatible with standard metric tapped holes, threaded inserts, and metric nuts of the same diameter and pitch. They are not compatible with UNC/UNF (inch) threads.

What hex key size do I need for each screw size?

The required hex key (Allen wrench) size by thread diameter is generally: M2 → 1.5mm, M2.5 → 2mm, M3 → 2.5mm, M4 → 3mm, M5 → 4mm, M6 → 5mm. Always do a test fit before applying full torque to confirm the key seats fully in the socket without play.

Can I use these screws in aluminum, plastic, or soft materials?

Yes, countersunk socket head screws are commonly used in aluminum enclosures, CNC-machined parts, and rigid plastic assemblies. Because Grade 10.9 alloy steel is significantly harder than aluminum or plastic, take care not to overtighten — use a torque wrench and follow the recommended torque specification for the thread size to avoid stripping the tapped hole or cracking the material. For plastic, consider using a thread-forming screw or a threaded insert for best results.

How do I decide which pack quantity to order?

For a single repair or prototype build, 10 pcs is generally sufficient. Workshop restocking or small production runs typically call for 30–50 pcs. For ongoing manufacturing or assembly lines, 100 pcs or 500 pcs offers a lower per-unit cost and reduces reorder frequency. All quantities ship in the same secure packaging from our US warehouse.

🛒 Select your thread diameter x length and quantity above, then add to cart — ships from our US warehouse.