Definition
A small threaded fastener, usually headless, used to hold one part in a fixed position relative to another by being tightened against it. Most setscrews have a recessed drive (such as a hex socket) and a tip that bites into or presses against the mating part to prevent slipping or rotation.
Plain English
A small screw used to lock one part onto another so it doesn't slide or spin. You tighten it down until its tip presses firmly against the part you want to hold in place.
Context Anchor
Seen in aircraft maintenance when checking knobs, collars, pulleys, levers, or other parts fastened to shafts or rods.
Derivation
From 'set' (to fix in place) plus 'screw'. The name describes its job: a screw whose purpose is to set something firmly in position rather than to clamp two parts together like an ordinary screw.
Why Pilots Care
Loose setscrews allow control surfaces, instruments, or engine parts to shift, creating unexpected handling or inaccurate readings that can affect safety.
Analogy
Like driving a pin through a wheel and its axle so the wheel cannot spin independently.
Intuition Check
A setscrew is not just any screw used during assembly. Its job is specifically to lock one part in position against another part.
Example Sentence 1
The mechanic tightened the setscrew on the control knob to keep it from slipping on the shaft.
Example Sentence 2
Before flight, the pilot checked that the setscrews securing the elevator trim tab linkage remained tight.