A self-tapping screw is a threaded fastener capable of forming its own threads; its thread cross-section features a non-circular profile, such as a trilobular or pentagonal shape.
Self-tapping screws belong to the coarse-pitch standard thread series, with thread specifications ranging from M3 to M12 mm. Within China's national standards for commercial fasteners, the category of self-tapping locking screws comprises five distinct series: GB/T6560 (Cross Recessed Pan Head), GB/T6561 (Cross Recessed Countersunk Head), GB/T6562 (Cross Recessed Raised Countersunk Head), GB/T6563 (Hex Head), and GB/T6564 (Internal Hexalobular Cylindrical Head).
Furthermore, there exist high-performance self-tapping locking screws with a surface hardness exceeding HRC56; this allows them to cold-extrude and form threads within workpieces possessing a surface hardness greater than HRC23.
