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Protruding screw heads, corroded fasteners, and stripped Phillips drives are the most common failure points in outdoor assemblies, marine fittings, and precision metalwork. These A4 (316) stainless steel countersunk flat head Allen socket machine screws solve all three: the tapered head sits flush with the surface for a clean, snag-free finish; the marine-grade A4 stainless resists rust and salt corrosion; and the hex (Allen) socket drive provides reliable torque without cam-out.
Available in thread diameters M3 through M10 and lengths from 4mm (0.16”) to 100mm (3.94”), these screws cover the full range of structural and precision fastening needs. The 90° countersunk head angle is compatible with standard metric countersunk holes. Pack sizes of 1, 5, 10, and 20 pieces let you order exactly what you need — from a single replacement to a workshop supply.
Typical applications include marine and coastal hardware (boat fittings, dock hardware, outdoor enclosures), architectural metalwork and stainless steel fabrication, precision machinery and equipment panels, outdoor furniture and structural brackets, and any application where a flush, corrosion-resistant fastener is required.
| Material | A4 Stainless Steel (316 / 316L) |
|---|---|
| Grade | A4-70 (typically) |
| Thread Standard | ISO Metric |
| Thread Diameters | M3, M4, M5, M6, M8, M10 |
| Head Style | Countersunk Flat Head (90° angle) |
| Drive Type | Hex (Allen) Socket — 2mm / 2.5mm / 3mm / 4mm / 5mm / 6mm |
| Available Lengths | 4mm (0.16”), 5mm (0.20”), 6mm (0.24”), 8mm (0.31”), 10mm (0.39”), 12mm (0.47”), 14mm (0.55”), 16mm (0.63”), 18mm (0.71”), 20mm (0.79”), 22mm (0.87”), 25mm (0.98”), 30mm (1.18”), 35mm (1.38”), 40mm (1.57”), 45mm (1.77”), 50mm (1.97”), 55mm (2.17”), 60mm (2.36”), 70mm (2.76”), 80mm (3.15”), 90mm (3.54”), 100mm (3.94”) |
| Pack Sizes | 1 / 5 / 10 / 20 pcs |
| Screw Type | Machine screw (requires tapped hole or nut) |
| Length Measurement | Including head (total length) |
| Corrosion Resistance | Excellent — marine-grade, suitable for saltwater and outdoor use |
| Common Applications | Marine hardware, outdoor structures, precision machinery, architectural metalwork, panel mounting |
For countersunk screws, length is measured including the head. The screw should sit flush with or just below the surface when fully driven into a properly countersunk hole. Engaged thread length should be at least 1× the thread diameter for metal. Available lengths run from 4mm (0.16”) to 100mm (3.94”). When in doubt, size up.
A4 is marine-grade stainless steel, equivalent to 316 or 316L stainless. It contains molybdenum, which gives it superior corrosion resistance compared to A2 (304) stainless — particularly in saltwater, chlorinated water, and acidic environments. A4 is the standard specification for marine and coastal fasteners.
Yes. A4 (316) stainless steel is the standard choice for marine, coastal, and outdoor applications. These screws are well-suited for boat fittings, dock hardware, outdoor furniture, coastal construction, and any application with prolonged moisture or salt exposure where A2 (304) stainless would corrode.
Allen (hex) key sizes by thread diameter: M3 = 2mm, M4 = 2.5mm, M5 = 3mm, M6 = 4mm, M8 = 5mm, M10 = 6mm. Use a quality hex key or Allen driver bit for best results. A worn or undersized key can round out the socket on smaller screws.
A countersunk (flat head) screw has a tapered head that sits flush with or below the surface when driven into a countersunk hole. Use them when a flush, snag-free surface is required — such as panels, hinges, brackets, and structural assemblies where a protruding head would interfere with fit or function.
Yes — these are machine screws, not self-tapping. They require a pre-tapped M-series hole or a matching metric nut in the same thread size. They will not cut their own thread into plastic or metal.
A4-70 stainless steel (the most common grade) has a minimum tensile strength of 700 MPa and proof load of 450 MPa. This is generally sufficient for structural and medium-load applications. For critical load-bearing use, verify the specific grade and consult torque specifications for the thread size.
Available in packs of 1, 5, 10, and 20 pieces. Single-piece packs are ideal for repairs and replacements; larger packs suit workshop stock and production use. Select your preferred quantity using the Qty option above.
