Self-tapping screws, also called quick-acting screws or quick-acting screws, can be drilled directly without drilling. I guess the reason for this name is that they can "attack" screws.
Even steel and stainless steel can't use self-tapping screws to drill internal threads in the material while screwing.
Self-tapping screws are generally used for materials with low hardness. For example, aluminum alloy threads are divided into external threads and internal threads. Generally speaking, the thread on the bolt is external thread, while the thread on the nut is internal thread.