The core difference is between "hole" and "tooth". Self-tapping screw (Self-tapping Screw) has high hardness and sharp teeth. It can directly "tap" threads on plastic, sheet or wood without pre-tapping; it is often used in electrical housings and gypsum boards. The thread precision of the machine thread (Machine Screw) is high, and it must be used with the nut or tapping hole with prefabricated internal thread for precision equipment with large force and need to be disassembled. Simple note: self-tapping is "self-made thread" and machine thread is "matching with existing thread". Incorrect selection can result in tooth slide or connection failure.