Definition
The distance a screw or bolt advances along its axis in one complete turn (360 degrees) of rotation. For a single-thread fastener, the lead equals the pitch (the distance between adjacent threads). For a multi-start thread, the lead equals the pitch multiplied by the number of starts.
Plain English
How far a screw moves forward when you turn it one full turn. On a normal single-thread screw, that distance is the same as the gap between two threads. On a screw with multiple thread starts, it moves forward farther per turn.
Context Anchor
Seen in aircraft maintenance discussions of threaded parts, screw-type adjusters, and parts that move by turning a screw.
Derivation
From the Old English laedan, meaning 'to guide' or 'to cause to go.' The thread 'leads' the fastener along its axis as it turns -- so 'lead' here means the distance the thread guides it forward, not the metal element.
Why Pilots Care
On flight-control jackscrews and trim mechanisms, the lead determines how quickly the surface moves for each turn of the screw. Mechanics need to distinguish lead from pitch when working with multi-start threads, because confusing the two can cause incorrect rigging or adjustment.
Intuition Check
Lead does not mean the front part of the screw here. It means the amount of straight-line movement produced by one full turn of the thread.
Example Sentence 1
The mechanic checked the lead of the jackscrew thread to confirm how far the trim surface would travel per revolution.
Example Sentence 2
Proper lead ensures the threaded part engages correctly without binding during propeller hub assembly.