Definition
A mechanical device used to produce very small, precise linear movements. It consists of two threaded sections on the same shaft with slightly different thread pitches. When the screw is turned, the net movement of the working part equals the difference between the two thread pitches, allowing motion finer than either thread alone could provide.
Plain English
A screw with two sets of threads cut at slightly different spacing, so each turn moves the part only a tiny amount — the small leftover difference between the two threads. It is used where you need very fine, controlled adjustment.
Context Anchor
Seen in aircraft maintenance and mechanical adjustment work where a part must be positioned very accurately.
Derivation
Differential comes from the Latin differentia, meaning 'a difference.' The name fits because the screw works on the difference between two thread pitches rather than the full travel of either one.
Why Pilots Care
Pilots rarely adjust differential screws directly, but mechanics use them when calibrating instruments and rigging controls. Knowing the term helps when reading maintenance manuals or discussing fine adjustments with a technician.
Analogy
It is like using two nearly equal pushes in opposite directions so that only a tiny leftover movement remains. That small leftover movement is what makes the adjustment precise.
Intuition Check
Do not read differential here as a general word for complicated or advanced. In this term, it means the useful movement comes from the difference between two thread movements.
Example Sentence 1
The technician used a differential screw to make a tiny correction to the instrument's zero setting.
Example Sentence 2
During instrument calibration, the differential screw allowed precise setting of the pointer zero.