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When a protruding screw head isn't an option — whether you're assembling electronics enclosures, mounting panels, building outdoor furniture, or fabricating marine hardware — an ordinary fastener creates snag points, clearance problems, and an unfinished look. These M3 M4 M5 flat head socket cap screws are engineered to sit perfectly flush with the surface, eliminating interference while delivering a clean, professional finish that engineers, makers, and contractors rely on.
Each screw features a countersunk flat head with an Allen (hex socket) drive recess, machined from 316 A4 stainless steel. The 316 grade adds molybdenum to the alloy, giving it substantially better resistance to chloride and saltwater corrosion compared to standard 304/A2 stainless. Available in three thread sizes — M3×0.5mm, M4×0.7mm, and M5×0.8mm — with screw lengths (including head) ranging from 4mm (≈5/32") to 60mm (≈2-3/8"), and pack quantities of 5, 10, 25, 50, or 100 pieces to match your project scale.
Typical applications include electronics chassis assembly and PCB standoff mounting, marine deck hardware and boat fittings where corrosion resistance is critical, outdoor signage and architectural metalwork, and precision mechanical assemblies where a flush countersunk fastener is required by design. The ISO metric coarse thread profile ensures compatibility with standard tapped holes, threaded inserts, and metric nuts across all three sizes.
| Product Type | Flat Head Socket Cap Screw (Countersunk, Allen Drive) |
|---|---|
| Thread Sizes Available | M3×0.5mm, M4×0.7mm, M5×0.8mm |
| Thread Standard | ISO Metric Coarse (ISO 68-1) |
| Head Style | Flat (Countersunk), 90° included angle |
| Drive Type | Hex Socket (Allen / Internal Hex) |
| Hex Key Size | M3 → 2mm | M4 → 2.5mm | M5 → 3mm |
| Screw Length Range (incl. head) | 4mm (≈5/32") – 60mm (≈2-3/8") |
| Material | 316 Stainless Steel (A4 per ISO 3506) |
| Corrosion Resistance | Excellent — suitable for marine and outdoor use |
| Property Class | Typically A4-70 (confirm for critical applications) |
| Pack Quantities | 5, 10, 25, 50, 100 pieces |
| Finish | Natural stainless (no coating) |
| Compatible Fasteners | Standard metric hex nuts, lock nuts, flat washers (M3/M4/M5) |
| Country of Fulfillment | Ships from US warehouse |
The listed length includes the head. For countersunk flat head screws, the head sits flush with the surface, so the full listed length is typically the grip length. As a general rule, choose a length that allows at least 1.5× the screw diameter of thread engagement in the receiving material — for example, an M4 screw should engage at least 6mm of thread. Lengths are listed in mm; to convert, 25mm ≈ 1 inch, so a 50mm screw is approximately 2 inches.
316 A4 stainless steel socket cap screws generally conform to ISO 3506 property class A4-70, with a minimum tensile strength of typically 700 MPa. Actual load capacity depends on the specific size and thread engagement depth. For critical structural or load-bearing applications, contact us to confirm specifications.
Yes. 316 A4 stainless steel contains molybdenum, which provides significantly better resistance to chloride corrosion compared to 304/A2 stainless. These screws are generally well-suited for marine deck hardware, coastal outdoor installations, boat fittings, outdoor furniture, and wet or humid conditions. For highly aggressive chemical environments, confirm suitability before use.
These screws use standard ISO metric coarse threads: M3×0.5mm pitch, M4×0.7mm pitch, and M5×0.8mm pitch. They are compatible with standard metric nuts, threaded inserts, and tapped holes following the ISO 68-1 thread profile — the most widely used metric thread standard globally.
Hex key sizes for these flat head socket screws are typically: M3 → 2mm hex key, M4 → 2.5mm hex key, M5 → 3mm hex key. Always use a properly fitting, high-quality hex key to avoid rounding the socket, especially when applying higher torque on larger sizes.
Choose based on load requirements and the clearance or tapped hole size in your application. M3 (3mm diameter) is suited for light-duty electronics, small brackets, and precision assemblies. M4 (4mm) is a versatile mid-range size for general mechanical assemblies and enclosures. M5 (5mm) handles heavier loads and is common in structural, industrial, and marine hardware applications. When in doubt, check the torque and shear requirements for your specific use case.
Yes. These screws follow standard ISO metric thread dimensions and are compatible with standard metric hex nuts, nylon lock nuts, flat washers, and spring washers of the corresponding size (M3, M4, or M5). For best corrosion resistance in marine or outdoor applications, pair with 316 stainless steel nuts and washers.
