A2 Stainless Steel Slotted Countersunk Machine Screws — M1.6 to M10, Flat Head CSK Bolts

For countersunk screws, the stated length includes the head. Measure the total thickness of the material being fastened, then add the depth of engagement needed in the base material — typically at least 1.5× the screw diameter. For example, an M4 countersunk screw through a 3mm panel into a tapped hole should generally be at least 9–12mm total length. Available lengths in this listing range from 3mm (≈1/8") to 100mm (≈3.9").

ISO metric countersunk machine screws typically use a 90° countersink angle. This is the standard angle for metric CSK screws and matches the most common countersink drill bits and pre-drilled countersunk holes in metal, plastic, and wood. Contact us to confirm if your application requires a different angle.

These screws are made from A2 stainless steel (304 grade), which generally offers good corrosion resistance for indoor and light outdoor use. They resist rust and oxidation better than standard carbon steel. For marine or highly corrosive environments, A4 (316) stainless steel is typically recommended. Contact us to confirm suitability for your specific application.

These are ISO metric machine screws with standard coarse-pitch threads (M1.6 through M10). They are compatible with standard metric nuts, threaded inserts, and tapped holes of the corresponding size. They are not compatible with UNC or UNF inch-standard threads used in some American hardware.

These screws use a slotted (flat-blade) drive. For smaller sizes like M1.6–M3, a narrow flat-blade screwdriver (typically 0.4–0.8mm blade width) is generally appropriate. For M4–M6, a medium flat-blade is typically used. For M8–M10, a wider flat-blade driver is generally needed. Always use a blade that fits snugly in the slot to avoid slipping and head damage, especially on smaller sizes.

Yes. The countersunk flat head is designed to sit flush with or below the surface of the material when installed in a properly drilled 90° countersunk hole. This makes them ideal for applications where a smooth, snag-free surface is required, such as panels, enclosures, furniture, and structural assemblies. The fit depends on the accuracy of the countersink hole — use a matching countersink bit for best results.

These are machine screws designed for use with pre-tapped holes, threaded inserts, or nuts — they are not self-tapping. They are suitable for metal, hard plastic, and composite materials where a threaded hole or nut is already in place. For wood applications, a threaded insert is generally recommended to ensure a secure, lasting hold.