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You’re assembling a steel frame, mounting a crane rail, or building a piece of heavy machinery – and you need a fastener that can handle serious loads without failing. These M1.6 to M3 countersunk socket head screws are made from 12.9 grade high‑strength carbon steel, offering exceptional toughness and tensile strength for demanding structural applications. The flat 90° head sinks flush into a pre‑drilled countersink, leaving a smooth surface. The hex socket (Allen) drive allows high torque without stripping. Lengths are measured overall (including the head), and screws are fully threaded. Ideal for steel beam connections, crane beams, braking systems, and any dynamic‑load joint where ordinary screws won’t last.
| Thread Diameter (M) | Overall Length (mm, including head) * | Thread Pitch (mm) | Head Style | Drive | Material / Grade |
|---|---|---|---|---|---|
| 📐 Overall length = from top of head to tip. Fully threaded. Select exact size from dropdown.夹 | |||||
| M1.6 | 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50 | 0.35 |
Countersunk / Flat (90°) |
Hex socket (Allen) |
12.9 Grade Carbon Steel |
| M2 | 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50 | 0.4 | |||
| M2.5 | 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50 | 0.45 | |||
| M3 | 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50 | 0.5 | |||
* Overall length includes the head. Fully threaded. Please allow minor manual measurement errors (±0.3mm). Hex key sizes: M1.6→1.5mm, M2→1.5mm, M2.5→2mm, M3→2mm (approx.).
| Property | 12.9 Grade | Standard Grade (4.8/8.8) |
|---|---|---|
| Tensile strength | ~1220–1370 MPa (very high) | ~400–800 MPa (moderate to high) |
| Yield strength | ~1080–1220 MPa | ~320–640 MPa |
| Typical use | Steel structures, crane beams, dynamic loads, heavy machinery | General assembly, furniture, light machinery |
| Hardness | Very high – wear resistant | Moderate |
| Corrosion resistance | Low (needs plating or oil for outdoor use) | Low |
1. How do I measure the length of these countersunk screws?
For countersunk flat head screws, the length is measured overall – from the top of the head to the tip. So an “M3 x 10mm” screw has a total length of 10mm including the head. This matches our listing.
2. Do I need to countersink the hole for these screws to sit flush?
Yes – these are true 90° countersunk screws. For a flush or slightly recessed finish, drill a matching 90° countersink hole. Use a countersink bit of the appropriate size.
3. Are these screws fully threaded? What about longer lengths like 50mm?
Yes – all M1.6 to M3 screws in this range (up to 50mm overall length) are fully threaded from under the head to the tip, giving you maximum grip.
4. Can I use these screws outdoors? Will they rust?
12.9 grade carbon steel has low inherent corrosion resistance. For outdoor or humid environments, we recommend applying a protective coating (paint, oil, or zinc plating). These screws are best for indoor structural use where strength is the priority. For marine or outdoor, choose stainless steel.
5. What hex key (Allen) size do I need for these small screws?
Approximate matching: M1.6 and M2 use 1.5mm, M2.5 and M3 use 2mm Allen key. Always use a quality hex key that fits snugly to avoid rounding the socket.
6. Can I use these screws with a nut? What size nut fits?
Yes – these are machine screws. Use standard metric nuts of the same thread size (M1.6, M2, M2.5, or M3 nut). For structural applications, use high‑strength nuts (Grade 10 or 12). They will also thread into pre‑tapped holes.
