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You’re assembling outdoor furniture, repairing marine equipment, or working on a project that demands a flush finish and long‑lasting rust protection. These M3.5, M4, and M5 countersunk screws are made from 304 stainless steel – the go‑to material for excellent wear, corrosion, and heat resistance. The Phillips flat head sinks perfectly into a pre‑drilled countersink, leaving a smooth, snag‑free surface. Available in lengths from 6mm up to 200mm measured under the head (excluding the head). Fully threaded for maximum grip. Ideal for machinery, electronics enclosures, boat fittings, and any application where a strong, low‑profile stainless fastener is needed.
| Thread Diameter (M) | Thread Pitch (mm) | Length Range (mm, under head) * | Head Style | Drive | Material |
|---|---|---|---|---|---|
| 📐 Length measured from underside of head to tip (excluding head). Fully threaded. Select exact size from dropdown. | |||||
| M3.5 | 0.6 (approx., common for M3.5) | 6, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 (exact availability varies by diameter) |
Countersunk / Flat (90°) | Phillips ( cross groove) |
304 Stainless Steel (A2) |
| M4 | 0.7 | ||||
| M5 | 0.8 | ||||
* Lengths are typical – exact availability may vary. Please allow minor manual measurement errors. Images are for reference only; actual product may vary slightly.
| Property | Benefit |
|---|---|
| Wear resistance | Withstands repeated assembly and disassembly without thread damage. |
| Corrosion resistance | Resists rust from moisture, salt air, and most chemicals – perfect for outdoor and marine use. |
| Heat resistance | Maintains strength in high‑temperature environments (up to ~800°C intermittent). |
| Deep threads | Standard cross groove ensures firm grip and reliable torque transfer with Phillips screwdrivers. |
1. How do I measure the length of a countersunk screw?
For countersunk flat head screws, the length is measured overall – from the top of the head to the tip. However, our listing specifies “length under head” (excluding head). Please check the dropdown carefully. The example M4 x 10mm means thread diameter 4mm, length from under head to tip is 10mm. The overall length including head would be approximately 10mm + 2mm (head height).
2. Do I need to countersink the hole for these screws to sit flush?
Yes – these are true 90° countersunk screws. To achieve a flush or slightly recessed finish, you must drill a matching 90° countersink hole. Use a countersink bit slightly larger than the head diameter.
3. Are these screws fully threaded? What about longer lengths like 200mm?
Yes – all M3.5, M4, and M5 screws in this range (up to 200mm) are fully threaded from under the head to the tip. This ensures maximum grip in blind holes or through‑nut applications.
4. Can I use these screws outdoors or in a marine environment?
Absolutely. 304 stainless steel is highly corrosion‑resistant and is the standard choice for outdoor furniture, marine hardware (above waterline), and coastal environments. For continuous saltwater immersion, consider 316 stainless, but for most applications, 304 is excellent.
5. What Phillips screwdriver size do I need for M3.5, M4, and M5?
For M3.5 and M4, use a #1 Phillips. For M5, a #1 or #2 Phillips works. Always use a driver that fits snugly to avoid cam‑out and head damage.
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 (M3.5, M4, or M5). Note that M3.5 nuts are less common but available. For M4 and M5, standard nuts are widely available. They will also thread into pre‑tapped holes.
