🌊 Product Overview: Countersunk Hex Socket Screws – A4 Stainless Steel (Marine Grade, M2–M16)
For applications where standard stainless steel isn’t enough – think saltwater, chemical plants, or coastal construction – these A4 (316) stainless steel countersunk hex socket screws deliver superior corrosion resistance. The 90° flat head sinks flush into countersunk holes, leaving a smooth, snag‑free surface. The internal hex (Allen) drive allows you to apply high torque without cam‑out, even in tight spaces. Made from marine‑grade A4 stainless (316), they offer excellent resistance to chlorides, oxidation, and heat, plus high strength and toughness. Available in metric sizes from M2 to M16, with lengths to suit your project. Fully threaded for maximum grip. Ideal for boat hardware, docks, chemical equipment, and any environment where rust is not an option.
✨ Why A4 Stainless Steel Countersunk Hex Screws Are the Premium Choice
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A4 stainless steel (316 / marine grade) – Contains molybdenum for exceptional resistance to saltwater, chlorides, and industrial chemicals. Outperforms A2 (304) in harsh environments.
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Countersunk flat head (90°) – Sits flush with the surface after countersinking. Perfect for marine decks, panels, and visible assemblies where a clean finish is required.
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Hex socket (Allen) drive – Internal hex provides positive engagement, eliminates cam‑out, and allows high torque without stripping the recess.
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Wide metric range: M2, M2.5, M3, M4, M5, M6, M8, M10, M12, M16 – From tiny electronics fasteners up to structural bolts for heavy marine and industrial use.
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Fully threaded (most sizes) – Threads run the entire length for maximum grip in thin materials. Length measured as total screw length including the head.
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High precision – DIN 7991 / ISO 10642 – Consistent head dimensions and thread geometry. See detailed table below for exact specs.
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Excellent mechanical properties – High strength, oxidation resistance, heat resistance, and superior toughness for demanding applications.
📏 Technical Specifications – Countersunk Hex Socket Screws (A4 Stainless, DIN 7991)
| Screw Size (d) |
Thread Pitch (p) |
Head Thickness (k) |
Head Diameter (dk) |
Hex Socket Size (s) |
Recommended Hex Key |
| M2 |
0.4 |
1.9 |
4.0 |
1.3 |
1.27mm / 1.3mm |
| All dimensions are in millimeters (mm). Length measurements include the head (total length). The above data were obtained through manual measurement and may contain minor errors. |
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| Size (d) |
Pitch (p) |
Head Thick (k) |
Head Dia (dk) |
Hex Size (s) |
Hex Key |
| M2 |
0.4 |
1.9 |
4.0 |
1.3 |
1.27-1.3mm |
| M2.5 |
0.45 |
2.5 |
5.0 |
1.5 |
1.5mm |
| M3 |
0.5 |
2.5 |
6.0 |
2.0 |
2.0mm |
| M4 |
0.7 |
3.4 |
8.0 |
2.5 |
2.5mm |
| M5 |
0.8 |
4.1 |
10.0 |
3.0 |
3.0mm |
| M6 |
1.0 |
4.9 |
12.0 |
4.0 |
4.0mm |
| M8 |
1.25 |
6.2 |
16.0 |
5.0 |
5.0mm |
| M10 |
1.5 |
7.6 |
20.0 |
6.0 |
6.0mm |
| M12 |
1.75 |
9.6 |
24.0 |
8.0 |
8.0mm |
| M16 |
2.0 |
10.0 |
29.0 |
10.0 |
10.0mm |
Note: Length measured as total screw length including head (e.g., M6 x 20mm = 20mm overall). All dimensions are manually measured – slight variations may occur. Refer to DIN 7991 / ISO 10642 for official standards.
❓ FAQs – A4 Stainless Steel Countersunk Hex Screws
🔸 What is the difference between A2 (304) and A4 (316) stainless steel?
A4 (316) contains molybdenum, which greatly improves resistance to chlorides – that means saltwater, de-icing salts, and many industrial chemicals. A2 (304) is fine for most indoor and general outdoor use, but A4 is the standard for marine, coastal, and chemical environments. It costs a bit more but lasts much longer in harsh conditions.
🔸 How is length measured for countersunk screws?
For countersunk screws, length is measured as total screw length including the head – from the top of the flat head to the tip. For example, an M6 x 20mm screw is 20mm long overall. This matches DIN 7991 / ISO 10642 standards. Countersunk holes should be drilled to accommodate the full length.
🔸 Will A4 stainless steel rust in saltwater?
A4 (316) stainless is highly resistant to saltwater corrosion and is the go‑to choice for boat hardware, dock fittings, and submerged applications. While no metal is completely immune to crevice corrosion in stagnant, low‑oxygen conditions, 316 performs excellently for most marine use. Rinse occasionally with fresh water for maximum lifespan.
🔸 What hex key (Allen wrench) size do I need for each screw diameter?
Refer to the table: M2 uses 1.3mm, M2.5 uses 1.5mm, M3 uses 2mm, M4 uses 2.5mm, M5 uses 3mm, M6 uses 4mm, M8 uses 5mm, M10 uses 6mm, M12 uses 8mm, M16 uses 10mm. A quality metric hex key set (1.5mm to 10mm) will cover all these sizes.
🔸 Can I use these screws with nuts, or are they for tapped holes only?
These are standard machine screws – they work perfectly with matching metric nuts or in pre‑tapped holes. For a flush finish, you would typically use them in countersunk holes without nuts. For through‑hole applications, pair with A4 stainless nuts and washers for complete corrosion protection.
🔸 What lengths are available for each diameter?
Lengths vary by size – typical ranges: M2–M3: 4–20mm, M4–M5: 6–30mm, M6–M8: 10–50mm, M10–M12: 16–80mm, M16: 25–100mm. Please select your desired length from the dropdown options. If you need a length not listed, contact us.
