Screw-thread motion: The axial distance a screw thread advances in one complete revolution is called the ________ (note: for a single-start thread this equals the pitch).

Introduction / Context:
Thread geometry defines how rotational motion converts to linear motion. Distinguishing lead from pitch is critical for power screws, jacks, and precise positioning systems.

Given Data / Assumptions:

• We consider standard single- and multi-start threads.
• We must name the axial advance per revolution.
• Basic thread terms are used: lead, pitch, crest, etc.

Concept / Approach:

Lead is the linear distance a nut (or screw) moves along the axis in one full turn. For single-start threads, lead = pitch. For an n-start thread, lead = n * pitch. The crest is the top of a thread, not a distance measure.

Step-by-Step Solution:

Verification / Alternative check:

Machine design texts and thread standards show the relationship lead = starts * pitch, validating the term’s definition.

Why Other Options Are Wrong:

Pitch: only equals lead for single-start; the definition asked specifically for axial advance per revolution.

Turn: descriptive word, not a standard thread parameter.

Crest: element of the profile, not a distance.

Common Pitfalls:

Assuming pitch and lead are always equal; this fails for multi-start screws where travel per turn is larger.

Final Answer:

Lead