12.9 Grade Torx Flat Head Machine Screws — Carbon Steel, M1.6 to M6

A general guideline: the engaged thread length in the base material should be at least 1.5–2× the screw diameter. For example, an M3 screw should typically engage at least 4.5–6mm of thread in the base. Measure the total stack thickness of all clamped layers, then add the required thread engagement depth. For a flush countersunk installation, also account for the head depth in your countersink — the head should sit at or below the surface, not above it.

Grade 12.9 is the highest common metric strength classification for machine screws. It indicates a minimum tensile strength of 1220 MPa and a proof load of approximately 1100 MPa. These screws are significantly stronger than Grade 8.8 or 10.9 fasteners and are typically used in high-stress mechanical assemblies, precision equipment, and applications where fastener failure is not acceptable. Always apply the correct torque specification for the diameter and grade to avoid over-tightening.

These are carbon steel screws without a specified corrosion-resistant coating. For outdoor, humid, or salt-spray environments, we recommend applying a thread-locking compound or anti-corrosion coating after installation, or contacting us to confirm whether a coated variant is available. For inherently corrosion-resistant fastening, stainless steel alternatives are generally a better choice.

Torx (six-lobe) bit sizes generally correspond to screw diameter as follows: T4–T5 for M1.6–M2, T6–T8 for M2.5–M3, T10–T15 for M3.5–M4, and T20–T25 for M5–M6. Always verify the exact socket size against your specific screw before applying torque, as sizing can vary slightly by manufacturer. Using an undersized bit can strip the recess; using an oversized bit will not seat properly.

The standard variants (50 pcs packs) are Grade 12.9 carbon steel Torx countersunk screws suitable for most high-strength fastening applications. The “High Hardness” variants (10 pcs packs) are additionally processed for greater surface hardness, making them suitable for applications with higher wear resistance requirements or where the screw must resist deformation under repeated torquing. Contact us to confirm the specific hardness specification if your application has defined requirements.

Torx (six-lobe) drive geometry distributes torque more evenly across six contact points, which significantly reduces cam-out — the tendency of the driver to slip out of the recess under high torque. This makes Torx drives well-suited for high-torque applications, automated assembly, and situations where repeated installation and removal are required without damaging the drive recess. Compared to hex socket (Allen) drives, Torx generally offers better torque transfer at smaller head sizes.

These screws follow the ISO metric thread standard with standard coarse pitch for each diameter (e.g., M3 × 0.5mm pitch, M4 × 0.7mm pitch). They are generally compatible with standard metric nuts, threaded inserts, and tapped holes of the corresponding diameter. Contact us to confirm pitch if fine-thread compatibility is required for your assembly.