304 Stainless Steel Phillips Flat Head Machine Screws M1–M6 | Countersunk Bolts

A general rule: the screw length should equal the thickness of the material being fastened plus enough thread engagement in the receiving part — typically 1.5× the screw diameter. For example, an M3 screw going through a 3mm (≈1/8") panel into a threaded insert generally needs at least 4–5mm of thread engagement, so M3×8mm (≈5/16") is a common choice. When countersinking, the flat head sits flush, so measure from the surface down. If in doubt, size up — you can always use a washer or adjust the countersink depth.

These screws are made from 304 stainless steel (A2 grade), which generally provides good corrosion resistance and moderate tensile strength — typically in the range of 500–700 MPa for A2 stainless, though exact values depend on the specific size and manufacturing batch. For high-load structural applications, please contact us to confirm specifications. For electronics, enclosures, RC models, and general assembly, 304 SS is generally well-suited.

304 stainless steel generally performs well in light outdoor and humid conditions, resisting rust and surface oxidation in most everyday environments. However, for prolonged marine exposure or highly corrosive chemical environments, 316 stainless steel is typically recommended. For occasional outdoor use — garden equipment, outdoor enclosures, brackets — these screws are generally suitable. Avoid contact with dissimilar metals in wet conditions to prevent galvanic corrosion.

These screws follow the ISO metric thread standard (M1 through M6). They are compatible with standard metric nuts, threaded brass inserts, and tapped holes conforming to ISO 68-1 thread profiles. They are not compatible with UNC or UNF inch-standard threads. If you are unsure whether your application uses metric or inch threads, measure the thread pitch with a thread gauge or check your assembly's engineering drawing.

The correct bit size depends on the screw diameter. As a general guide: M1–M1.6 typically requires a PH000 or PH00 bit; M2–M2.5 generally uses PH0; M3–M4 is typically PH1; M5–M6 is typically PH2. Using the correct bit size is important — an oversized bit will cam out and damage the head, especially on small screws. A precision screwdriver set with PH000–PH2 bits covers the full range.

Phillips countersunk (flat head) machine screws typically have a 90° head angle per ISO 7046 / DIN 965 standards. To achieve a flush or sub-flush installation, you need to countersink your material to match this angle. Without countersinking, the head will sit proud of the surface. Most standard countersink drill bits for metric screws are designed for 90°. Confirm your countersink angle matches before drilling.

Yes — the small sizes (M1–M2.5) are commonly used in electronics enclosures, PCB standoff mounting, laptop and camera assemblies, and RC model frames. The flat head profile keeps a low profile and sits flush, which is important in tight assemblies where clearance is limited. M3 and M4 are popular in 3D printer frames, drone arms, and hobby robotics. The stainless material is generally non-magnetic, which is a consideration for some sensor-sensitive electronics builds.