A general rule: the screw length should equal the thickness of the material being fastened plus enough thread engagement in the base material — typically 1.5× the screw diameter (≈4.5 mm for M3). For example, joining a 3 mm panel to a base would generally call for a 6–8 mm screw. Available lengths here range from 3 mm (≈1/8") to 15 mm (≈19/32"). When in doubt, size up — you can always trim thread engagement with a washer, but a screw that's too short won't hold.

The head diameter determines how wide the countersink recess needs to be. A larger head spreads clamping load over a wider area, which is generally better for softer materials like wood or plastic. For metal-to-metal applications, a smaller head (4.3–4.8 mm) typically fits standard countersink tooling. Check your countersink bit spec or pre-drilled hole diameter before selecting a variant.

Carbon steel M3 screws are generally rated at property class 4.8 or higher, providing adequate tensile strength for light-to-medium duty assembly tasks such as electronics chassis, 3D printer frames, and thin-panel fixtures. For precise load ratings in structural or safety-critical applications, contact us to confirm the specific grade for your chosen variant.

Black zinc and white zinc coatings offer moderate corrosion resistance suitable for indoor and sheltered applications. Bright nickel provides a decorative finish with similar protection levels. For prolonged outdoor exposure, coastal environments, or direct water contact, stainless steel fasteners are generally recommended. Contact us if you need guidance on finish suitability for your specific environment.

These are metric M3 screws with a standard coarse thread pitch of 0.5 mm, fully compatible with M3 nuts, M3 threaded inserts (heat-set or press-fit), and tapped holes following ISO metric standards. They are not compatible with UNC or UNF inch-standard threads. If you're using them with heat-set inserts in 3D-printed parts, M3 × 0.5 is the most common insert size.

The Black Zinc With Glue variant features a factory-applied thread-locking adhesive patch on the threads. This patch activates under the clamping pressure of installation and helps prevent loosening from vibration — no separate liquid threadlocker needed. It is well-suited for motor mounts, fan brackets, machinery panels, and any assembly subject to repeated vibration or thermal cycling.

Choose based on your aesthetic and environment: Black Zinc gives a matte dark appearance commonly used in electronics enclosures, automotive interiors, and industrial equipment. White Zinc provides a silver-grey look with solid general-purpose corrosion resistance. Bright Nickel delivers a shiny, polished finish suited for visible consumer product assemblies where appearance matters. All three finishes are applied over carbon steel.

These M3 flat head screws are available in 100, 200, 300, 400, and 500-piece packs. For a single project, 100 pcs is typically sufficient for most small assemblies. Workshop restocking or production runs benefit from 300–500 pcs packs, which offer a lower per-unit cost. Mix and match sizes and finishes across separate orders to build a complete M3 fastener kit.