Keywords: Self-tapping screws; Screws (bolts); External-thread fasteners; Threaded fasteners; Fasteners; Drilling; Heat-treatable steels; Case-hardening steels; Steels; Heat treatment; Mechanical properties of materials; Surface properties; Hardness; Torsional strength; Strength of materials ; Torsion testing; Mechanical testing; Crystal microstructure; Embrittlement; Hardness measurement ; Inspection; Performance testing; Test equipment ; Testing conditions; Test specimens