KM3/KM4 Phillips Flat Head Triangle Tooth Screws | Carbon Steel, Zinc or Nickel Coated

KM screws (also called triangle tooth or tri-lobe thread screws) feature a triangular thread profile rather than a standard V-thread. This design allows the screw to cut or form its own mating thread as it is driven into softer materials such as plastic, aluminum, or thin sheet metal — reducing the need for pre-tapped holes. The triangular thread also generally provides better resistance to loosening under vibration compared to standard machine threads. Standard M3/M4 machine screws require a pre-tapped hole with matching thread pitch; KM screws do not, in most plastic and soft-metal applications.

KM3 (3mm thread diameter, ≈0.118") is typically used for lighter-duty assemblies, thin panels, small enclosures, and electronics housings. KM4 (4mm thread diameter, ≈0.157") is generally suited for heavier panels, thicker plastic housings, and applications requiring more clamping force. For length: the screw should be long enough to engage at least 2× the thread diameter in the receiving material — so KM3 generally needs at least 6mm (1/4") of thread engagement, and KM4 at least 8mm (5/16"). Choose the shorter length for thin materials and the longer for thicker substrates.

Both are KM3 (3mm thread diameter) screws with the same 6mm length, but with different head outer diameters. D=5.5mm has a smaller head footprint, useful when clearance around the screw head is limited or when your countersink hole is sized for a smaller head. D=6mm has a slightly larger head, providing more bearing surface and clamping area. Measure your countersink hole diameter before ordering to ensure the head fits flush without rocking or protruding.

White zinc plating provides general corrosion resistance and a silver-gray appearance suitable for most indoor applications. Black zinc offers the same corrosion protection with a darker, matte-black finish often preferred for electronics, dark-colored enclosures, or products where silver hardware would stand out. Nickel-plated screws provide a bright, polished appearance and slightly enhanced corrosion resistance, commonly used in consumer electronics and appliances where appearance matters. All three coatings are generally suitable for indoor use; none are recommended for prolonged outdoor or marine exposure without additional protection.

KM triangle tooth screws are designed to cut or form their own threads in softer materials such as plastic, aluminum, and thin sheet metal, so a pre-tapped hole is generally not required in those materials. However, a pilot hole of the correct diameter is always recommended to guide the screw and prevent cracking or splitting, especially in brittle plastics. For KM3, a pilot hole of approximately 2.5–2.7mm is typically used in plastic; for KM4, approximately 3.3–3.5mm. Consult the material manufacturer’s recommendations for exact pilot hole sizing. For harder metals, pre-tapping is generally required.

These screws are made from carbon steel, which generally provides higher tensile strength than same-size stainless steel. The triangle tooth thread profile also tends to resist loosening under vibration better than standard V-thread machine screws, because the thread flanks create a locking effect as they form into the mating material. Exact tensile strength values depend on the specific carbon steel grade and heat treatment; contact us to confirm if your application has specific load or torque requirements.

The zinc and nickel coatings on these carbon steel screws provide moderate corrosion resistance suitable for indoor and sheltered environments. For prolonged outdoor exposure, especially in humid, wet, or salt-air conditions, additional protection (such as a sealant or conformal coating over the assembly) is generally recommended, or consider using 304 stainless steel screws instead. These screws are not recommended for marine or highly corrosive environments without additional protection.