Generally refers to pointed, coarse-toothed, hard-textured wood screws, but also aluminum alloys and plastics. A special self-tapping screw used to thread metal holes is called a tap.
Self-tapping screws are used for non-metal or softer metals, and do not need to drill and tap; self-tapping screws are pointed, so that they can "self-tapping"; ordinary screws are flat-headed and have the same thickness.
The self-tapping screw means: the drilled hole is a hole that does not need to be tapped. The screws used are different from the general ones. The head is pointed and the pitch is relatively large. It is a bit like a chipless tap , and it can be directly screwed in without tapping., Metals and plastics usually use this method.
It can be consolidated in the material, by its own thread, the consolidated body is "attack-drilling, squeezing, pressing" the corresponding threads, so as to mate with each other.
