Definition
A hardened screw with specially formed threads that cut their own mating threads into the material as the screw is driven in, eliminating the need to pre-thread the receiving hole. A pilot hole of the correct diameter is typically still required.
Plain English
A screw that creates its own threads in the material as you drive it in, so you don't have to thread the hole first.
Context Anchor
Seen in aircraft maintenance, especially around light panels, fairings, interior trim, and other parts where the maintenance instructions call for this type of screw.
Derivation
Self-tapping' means the screw does its own 'tapping' — tapping is the metalworking term for cutting internal threads in a hole. So the screw taps (cuts) its own threads as it goes in.
Why Pilots Care
Allows secure fastening in locations where pre-tapping a hole would be difficult or would weaken the structure.
Intuition Check
A self-tapping screw does not mean the screw can be used anywhere. It means the screw is made to form its own threads in the correct kind of prepared hole.
Example Sentence 1
The mechanic used self-tapping screws to secure the new access panel to the fuselage skin.
Example Sentence 2
During the preflight, we noticed a loose screw and replaced it with a self-tapping screw of the correct length and diameter.