🔩 M3–M12 Countersunk Hex Socket Screws – 316 Stainless Steel (A4), DIN7991, 4–100mm
When a flush finish and extreme corrosion resistance are non‑negotiable, reach for these 316 stainless steel countersunk hex socket screws. The flat 90° head sits perfectly flush in a countersunk hole – no snagging, no protruding metal. The internal hex drive (Allen key) delivers high torque without slipping, and A4 (316) stainless stands up to saltwater, chemicals, and coastal humidity. Available from M3 up to M12, with lengths from 4mm to 100mm (overall length including head). Choose your pack quantity (1, 3, 5, 10, 20, or 40). Perfect for marine hardware, chemical plants, outdoor machinery, and precision equipment.
✨ Why These 316 Stainless Countersunk Hex Screws
- 🧪 316 stainless steel (A4 grade) – Molybdenum‑enhanced for superior pitting and chloride resistance. Ideal for marine, coastal, and chemical environments.
- 🔽 Countersunk flat head (90°) – Flush fit with any standard countersink. No protruding heads to catch tools or clothing.
- 🛠️ Hex socket drive (Allen) – Internal hex allows high torque transfer with zero cam‑out. Use standard metric hex keys.
- 📏 Full metric range M3 to M12 – Seven diameters cover electronics (M3) to heavy machinery (M12).
- 📐 Lengths from 4mm to 100mm (overall) – Overall length includes the head – simply measure from top to tip.
- 📦 Flexible pack quantities – 1, 3, 5, 10, 20, or 40 pieces per pack.
- 🏭 DIN7991 / GB standard – Precision metric threads, natural stainless finish.
📏 Available Sizes – M3 to M12 Countersunk Hex Screws (316 Stainless)
| Thread Size |
Length Range (overall, mm) |
Typical Applications |
| M3 |
4 – 50 |
Electronics, 3D printers, marine instruments |
| M4 |
5 – 70 |
Furniture, boat deck fittings, light machinery |
| M5 |
6 – 80 |
Equipment enclosures, marine hardware |
| M6 |
6 – 100 |
Heavy machinery, boat engines, outdoor fixtures |
| M8 |
8 – 100 |
Automotive, industrial equipment, deck rails |
| M10 |
10 – 100 |
Structural connections, machinery bases |
| M12 |
12 – 100 |
Crane components, large marine fixtures |
📌 Length measured from the top of the head to the tip (overall). Example: M6×30 = M6 thread, 30mm overall length.
📋 Full Specifications – DIN7991 Countersunk Hex Socket Screws (316)
| Parameter |
Details |
| Material |
316 stainless steel (A4) with molybdenum |
| Head style |
Countersunk flat head, 90° included angle |
| Drive style |
Hex socket (Allen key) |
| Thread sizes |
M3, M4, M5, M6, M8, M10, M12 |
| Length range |
4mm – 100mm (overall, varies by size) |
| Standard |
DIN7991 / GB (metric) |
| Surface |
Untreated, natural stainless |
| Pack quantities |
1, 3, 5, 10, 20, 40 pieces |
| Applications |
Marine hardware, chemical plants, outdoor machinery, electronics, automotive |
📌 Stainless steel grade guide:
• 201 stainless – Dry use only, rusts with water.
• 304 stainless (A2) – Good for outdoor/humid, corrosion resistant.
• 316 stainless (A4) – Added molybdenum → superior pitting and chloride resistance. Ideal for seawater, chemicals, and salt spray. This product is 316.
❓ Frequently Asked Questions – Countersunk Hex Socket Screws (M3–M12, 316)
1. What hex key (Allen wrench) size do I need for each screw size?
M3 = 2mm, M4 = 2.5mm, M5 = 3mm, M6 = 4mm, M8 = 5mm, M10 = 6mm, M12 = 8mm. Always use a good quality metric hex key that fits snugly to avoid rounding the socket.
2. Why choose 316 (A4) over 304 (A2) stainless?
316 contains molybdenum, which dramatically improves resistance to pitting and corrosion from chlorides – saltwater, deicing salts, pool chemicals. If your project will be near the ocean, on a boat, or exposed to harsh chemicals, 316 is the right choice. For general outdoor use, 304 is adequate, but these screws are 316 for maximum durability.
3. How do I measure the length correctly?
For countersunk screws, length is the overall length – from the top of the head to the tip. Place the screw head‑down on a ruler; measure to the tip. Our lengths (4–100mm) are overall.
4. Can I use these with nuts or only into tapped holes?
Both. They are standard machine screws – use with matching metric nuts (M3–M12) or into pre‑tapped holes. For a flush finish on the nut side, add a countersunk washer or flat washer.
5. Are these screws fully threaded?
Lengths up to about 60mm are fully threaded. Longer lengths (70–100mm) may have a short unthreaded shank under the head. If you need fully threaded for a specific long size, please contact us.
6. What pack quantities are available?
You can order 1, 3, 5, 10, 20, or 40 pieces per pack. Select your desired quantity in the product options.
