Threads, Fasteners & Springs — The root of a thread is the bottom surface joining the two flanks; the crest is the top surface. Therefore, calling the root “the top surface” is incorrect.

Introduction / Context:Thread terminology distinguishes between crest (top), root (bottom), and flanks (sides). Correct identification is vital for specifying tolerances, fillet radii at roots, and evaluating stress concentrations.

Given Data / Assumptions:

• Crest = top surface of the thread profile.
• Root = bottom surface connecting the flanks.
• Flanks = inclined sides of the profile between crest and root.

Concept / Approach:Because stress often peaks at the root, standards specify root radii/clearances to reduce fatigue risk. Mislabeling crest and root causes drawing errors and inspection mistakes.

Step-by-Step Solution:1) View a single pitch segment of the thread profile.2) Identify the highest surface—this is the crest.3) Identify the lowest surface between flanks—this is the root.4) Conclude the statement is incorrect.

Verification / Alternative check:Cross-sectional diagrams in standards consistently label crest at the top and root at the bottom of the profile.

Why Other Options Are Wrong:Equating crest and root, or placing root at a midline, contradicts accepted definitions; pitch does not determine which is crest/root.

Common Pitfalls:Reversing crest/root in callouts; omitting root radius leading to crack initiation.

Final Answer:Incorrect