Self-tapping screws are threaded fasteners capable of forming their own threads; their thread cross-sections feature specialized profiles-such as trilobular or pentagonal shapes-that utilize cold extrusion to create internal threads within a pre-drilled hole, thereby enabling an interference fit without the need for a pre-tapped hole. Manufactured from carburized or alloy steel, these screws undergo surface hardening treatments to achieve low driving torque, high clamping performance, and anti-loosening capabilities. Their surface hardness can exceed Rockwell Hardness C56, and available thread specifications range from M3 to M12. Structurally, they consist of a head, shank, and tip, and are available in various configurations-including Phillips pan heads and hexagonal heads-making them widely utilized for connections in vibration-prone environments across sectors such as automotive, motorcycle manufacturing, and electronics.
Within the domestic automotive industry, the adoption of these fasteners has been gradually advanced through the introduction of foreign technology. Material selection has evolved from low-carbon steel to medium-carbon alloy steels-specifically 35CrMo-to enhance structural strength. The manufacturing process employs cold heading and specialized thread-rolling techniques, coupled with shallow-layer carburization heat treatments; this regimen ensures a surface hardness exceeding 45 HRC while maintaining a core toughness within the range of 28–39 HRC. Since the turn of the 21st century, patented technologies have driven structural innovations-such as pentagonal thread cross-sections that increase contact area, and triangular cutting grooves that generate multi-point resistance torque-resulting in a 50% to 60% increase in locking torque and a further optimization of anti-loosening performance.
