🔩 Grade 10.9 High Tensile Countersunk Socket Screws – Allen Key Flat Head Bolts M3 to M8 | DIN7991
🏷️ Brand: HomeDIYer Fastener | DIN7991 | Grade 10.9 Steel | Black Uncoated | Hex Bits Included
📌 Overview — Flush-fit strength for the most demanding assemblies. When you need a completely smooth surface and extreme clamping force, our Grade 10.9 High Tensile Countersunk Socket Screws (DIN7991) deliver. With a tensile strength of 1040 MPa (151,000 psi), these fasteners are significantly stronger than standard stainless or Grade 8.8 hardware. The 90° flat head sits flush with or below the workpiece surface, providing a clean, snag-free finish ideal for machinery guards, tooling fixtures, automotive components, and structural applications where protrusions are unacceptable. The hex socket drive (Allen key) allows high torque without cam-out, and we include the correct bits with your order. Fully threaded from M3 to M8, these screws are measured overall (including the head). Choose your exact length and quantity – engineered for professionals who demand both strength and a flush finish.
✨ Key Features – Grade 10.9 Countersunk Socket Screws
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Grade 10.9 High Tensile Alloy Steel – 1040 MPa tensile strength, 900 MPa yield strength – ideal for high-stress, safety-critical applications.
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Countersunk 90° Flat Head – Sits flush with or below the surface when installed in a countersunk hole – no snagging, no protruding heads.
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Hex Socket Drive (Allen Key) – Enables high torque transfer without cam-out; hex bits included with your order (2mm to 5mm).
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DIN7991 Standard – Precision metric threads and head geometry for reliable fit in standard countersunk holes.
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Fully Threaded – Threads run the entire length for maximum grip; length is measured overall (includes head).
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Metric Coarse Threads M3–M8 – Standard pitches: M3x0.5, M4x0.7, M5x0.8, M6x1.0, M8x1.25.
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Black Self-Color (Uncoated) Finish – Natural steel with light oil for storage; suitable for dry or oil-lubricated environments.
📏 Technical Specifications – Countersunk Socket Screws (DIN7991, Metric Coarse)
| Thread Size |
Thread Pitch (mm) |
Allen Key Size (mm) |
Head Diameter (mm) |
| M3 |
0.5 |
2.0 |
6.0 |
| M4 |
0.7 |
2.5 |
8.0 |
| M5 |
0.8 |
3.0 |
10.0 |
| M6 |
1.0 |
4.0 |
12.0 |
| M8 |
1.25 |
5.0 |
16.0 |
💡 Length & ordering info: Screws are fully threaded. Length is measured overall (including the head) – this is standard for countersunk screws. Choose your preferred overall length (e.g., 6mm, 8mm, 10mm, 12mm, 16mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm) — sold as per your requirement. Hex bits are included with your order – one bit per size or a multi-bit driver, depending on the pack.
⚠️ Material note: Grade 10.9 steel offers exceptional strength but is not corrosion-resistant. The black uncoated finish has light oil to prevent rust during storage. For indoor, dry, or oil-lubricated applications (engines, machinery, tooling), these are ideal. For outdoor or wet environments, use stainless steel or apply a protective coating.
❓ Frequently Asked Questions – Grade 10.9 Countersunk Socket Screws
How is the length measured for countersunk screws?
📏 For DIN7991 countersunk socket screws, the length is measured overall – from the top of the head to the tip. This is different from hex head or button head screws (which measure under the head). Always verify your required length based on the overall measurement.
Do I need to countersink the hole before using these screws?
🔧 Yes. For the head to sit flush with the surface, you must pre-drill a 90° countersink. These screws are not self-countersinking. Proper countersinking ensures a professional finish and prevents material cracking (especially in metal or plastic).
What hex key/bit do I need? Do you include them?
🔩 M3 → 2mm, M4 → 2.5mm, M5 → 3mm, M6 → 4mm, M8 → 5mm. Yes, the box includes the correct hex screwdriver bits for the screws you order – no need to buy tools separately.
How strong is Grade 10.9 compared to other grades?
📊 Grade 10.9 has a minimum tensile strength of 1040 MPa (151,000 psi) and a yield strength of 900 MPa. For comparison: Grade 8.8 is 800 MPa, A2-70 stainless is 700 MPa. These are excellent for high-stress bolted joints in machinery, automotive, and structural applications.
Will these screws rust? Are they suitable for outdoor use?
🌧️ Grade 10.9 steel is not stainless – it will rust if exposed to moisture. The black uncoated finish has light oil for storage, but for outdoor or wet environments, we recommend applying a rust-preventative coating (paint, zinc spray) or switching to A2/A4 stainless steel countersunk screws. These are best for dry, indoor, or oil-wetted applications.
⚙️ HomeDIYer Fastener — High-strength flush-mount fasteners for demanding applications. Order your exact size, length, and quantity today.
