What screwdriver or bit do I need to drive these screws?

These screws use a Phillips (cross) drive. For M5 and M6, a PH2 bit is typically used; for M8, a PH3 bit is generally recommended. Using the correct bit size reduces the risk of cam-out and head damage.

Can I use these screws with a power drill or impact driver?

Yes, these screws are compatible with power drills and impact drivers. Use a clutch setting appropriate for the material to avoid over-torquing, which can strip the Phillips drive or damage the countersunk seat.

M5 M6 M8 Phillips Flat Head Countersunk Machine Screws – A4 316 Stainless Steel - HomeDIYer

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M5 M6 M8 Phillips Flat Head Countersunk Machine Screws – A4 316 Stainless Steel

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By HomeDIYer®

Thread Diameter: M5

Length (mm): 8mm

Packing QTY (Piece): 5 PCS

Price:

$2.43 USD

Stock:

In stock (500 units), ready to be shipped

Quantity:

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M5 M6 M8 Phillips Flat Head Countersunk Machine Screws — Flush-Fit Fastening in A4 316 Stainless Steel

Whether you're assembling marine hardware, mounting panels on a boat deck, or securing fixtures in a coastal environment, finding fasteners that won't rust out after a single season is a real challenge. These M5, M6, and M8 Phillips flat head countersunk machine screws are made from A4 316 stainless steel — the go-to grade for anyone who needs reliable corrosion resistance in demanding conditions.

Each screw features a flat countersunk head with a Phillips (cross) drive, designed to sit flush with or below the surface of the material. Available in thread diameters of M5, M6, and M8, with lengths ranging from 8mm (≈5/16") to 100mm (≈3-15/16"). Packing options range from 1 to 50 pieces per order, so you can grab exactly what you need — no more, no less.

These screws are a natural fit for marine deck fittings, stainless steel fabrication, outdoor furniture assembly, and general-purpose metric fastening where a clean, flush finish matters. The flat countersunk head makes them especially useful for applications like hinge mounting, panel fastening, and flush-surface installations where a protruding head would be a snag hazard or aesthetic issue.

🔩 Compatibility: ISO metric thread standard — fits standard M5, M6, and M8 metric nuts, threaded inserts, and tapped holes. Not compatible with UNC/UNF inch-standard threads.

⚠️ Note: Pre-drill and countersink your material for a flush finish. Confirm thread pitch and hole diameter before ordering. If you need a specific grade certification, contact us to confirm.

✅ Key Features of These A4 316 Stainless Countersunk Machine Screws

🌊Marine-Grade A4 316 Stainless Steel — Contains molybdenum for superior resistance to chloride and saltwater corrosion, making these screws a reliable choice for marine deck hardware and coastal outdoor installations.
🔧Phillips Flat Countersunk Head — The 90° countersunk profile sits flush with the surface when properly installed, eliminating snag points and delivering a clean, professional finish on panels, hatches, and fixtures.
📏Wide Size Range: M5, M6, M8 × 8–100mm — Covers the most common metric machine screw sizes for general fabrication, furniture assembly, and structural fastening without needing multiple suppliers.
📦Flexible Pack Quantities (1–50 PCS) — Order exactly what your project requires — from a single replacement screw to a bulk pack of 50 for production runs or workshop stock.
⚙️ISO Metric Thread Standard — Full compatibility with standard metric nuts, threaded inserts, and tapped holes used in European and international manufacturing specifications.
🏗️Versatile Application Profile — Suitable for stainless steel fabrication, outdoor furniture, hinge mounting, panel fastening, and any application where a flush-surface countersunk machine screw is required.

📐 Technical Specifications — Phillips Flat Head Countersunk Machine Screws

Material	A4 316 Stainless Steel
Grade	A4 (ISO 3506)
Drive Type	Phillips (Cross / PH)
Head Type	Flat Countersunk (90° angle)
Thread Standard	ISO Metric (M5, M6, M8)
Thread Type	Fully threaded (typically); see variant options for partial thread on longer lengths
Available Diameters	M5, M6, M8
Available Lengths	8mm (≈5/16") to 100mm (≈3-15/16")
Packing Options	1, 2, 5, 10, 20, 50 PCS
Finish	Natural stainless (no coating)
Recommended Bit	PH2 (M5/M6), PH3 (M8) — see variant options
Corrosion Resistance	Excellent — suitable for marine and outdoor use
Country of Origin	Contact us to confirm

❓ Frequently Asked Questions

How do I choose the right length for my project?

A general rule of thumb is to select a screw length that is 2–3 times the thickness of the material being fastened. For example, if you are fastening a 5mm (≈3/16") panel, a 12–16mm (≈1/2"–5/8") screw is typically appropriate. Always account for the countersunk head depth, which is generally 1–2mm depending on the drive size. When in doubt, go slightly longer and use a nut or threaded insert on the back side.

What is the load-bearing or shear strength of these screws?

A4 316 stainless steel machine screws generally offer a tensile strength of around 500–700 MPa depending on diameter and specific production batch. For critical structural or load-bearing applications, consult a qualified engineer and request grade certification documentation. These screws are well-suited for general fastening, panel mounting, and marine hardware — not for primary structural connections in high-load scenarios.

Are these screws suitable for outdoor or marine use?

Yes. A4 316 stainless steel contains molybdenum, which significantly improves resistance to chloride-induced corrosion compared to standard A2 304 stainless. These screws are well-suited for marine deck hardware, coastal outdoor furniture, boat fittings, and any environment with regular exposure to saltwater, humidity, or chemical cleaning agents.

What thread standard do these screws use — are they compatible with my nuts?

These screws follow the ISO metric thread standard (M5, M6, M8). They are compatible with standard metric nuts, threaded inserts, and tapped holes. They are not compatible with UNC or UNF inch-standard threads. If you are unsure, check your existing hardware with a thread gauge before ordering.

What screwdriver or bit size do I need?

These screws use a Phillips (cross) drive. For M5 and M6 sizes, a PH2 bit is typically the correct fit. For M8, a PH3 bit is generally recommended. Using the correct bit size is important — an undersized bit will cam out and damage the drive recess, especially in stainless steel which can work-harden quickly.

Can I use a power drill or impact driver with these screws?

Yes. These screws are compatible with power drills and impact drivers. Set your clutch to a moderate torque level appropriate for the material. Over-torquing can strip the Phillips drive or crack the countersunk seat in harder materials. For stainless steel fasteners, applying a small amount of anti-seize compound is generally recommended to prevent galling during installation.

Do I need to pre-drill a countersunk hole for a flush finish?

Yes, for a proper flush or sub-flush installation, pre-drill a pilot hole and use a countersink bit matched to the screw head diameter. As a general guide: M5 screws typically require a ~10mm countersink, M6 requires ~12mm, and M8 requires ~16mm. Pre-drilling also prevents splitting in wood and cracking in brittle composite materials.

🛒 Select your thread diameter, length, and pack quantity above, then add to cart — ships from our US warehouse.