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You’re bolting down deck hardware on a boat, installing chemical plant equipment, or assembling something that lives in saltwater – and 304 stainless just isn’t enough. These M6, M8, and M10 socket countersunk screws are made from 316 stainless steel, which contains molybdenum for superior resistance to chlorides, saltwater, and industrial chemicals. The flat 90° head sinks flush into a pre‑drilled countersink, leaving a smooth, snag‑free finish. The hex socket (Allen) drive lets you apply high torque without slipping. Lengths are measured overall (including the head), and every screw is fully threaded. Perfect for marine rigging, docks, chemical processing, paper mills, and any environment where corrosion is a constant battle.
| Thread Diameter | Overall Length (mm, including head) * | Thread Pitch (mm) | Head Style | Drive | Material |
|---|---|---|---|---|---|
| 📐 Overall length = from top of head to tip. Fully threaded. Select exact size from dropdown. | |||||
| M6 | 10, 12, 16, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80 | 1.0 |
Countersunk / Flat (90°) |
Hex socket (Allen) |
316 Stainless Steel |
| M8 | 10, 12, 16, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 | 1.25 | |||
| M10 | 12, 16, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 | 1.5 | |||
* Lengths are typical – exact availability may vary. Please allow minor manual measurement errors. Hex key sizes: M6→4mm, M8→5mm, M10→6mm (approx.).
| Property | 316 Stainless (A4) | 304 Stainless (A2) |
|---|---|---|
| Corrosion resistance | Excellent – resists saltwater, chlorides, acids (contains 2‑3% molybdenum) | Good – not recommended for continuous saltwater exposure |
| Typical applications | Marine hardware, chemical plants, paper mills, food processing, coastal construction | General outdoor, furniture, automotive trim, light marine |
| Strength | Similar to 304 – A4‑70 grade (~700 N/mm²) | A2‑70 grade (~700 N/mm²) |
| Cost | Higher – premium marine grade | Lower – general purpose |
1. How do I measure the length of these countersunk screws?
For countersunk screws, the length is measured overall – from the top of the head to the tip. So an “M8 x 20mm” screw has a total length of 20mm 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 100mm?
Yes – all M6, M8, and M10 screws in this range (up to 100mm overall length) are fully threaded from under the head to the tip, ensuring maximum grip.
4. Can I use these screws in saltwater? Are they truly marine grade?
Absolutely. 316 stainless is the standard for marine applications – boat hardware, dock fittings, underwater equipment, and coastal structures. It resists pitting and crevice corrosion far better than 304. For continuous saltwater immersion, 316 is the correct choice.
5. What hex key size do I need for M6, M8, M10?
Approximate matching: M6 uses 4mm, M8 uses 5mm, M10 uses 6mm 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 (M6, M8, M10). They will also thread into pre‑tapped holes. Not self‑tapping – for wood or plastic, use a threaded insert or nut on the back.
