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Thread Crest Definition

Crest of a thread profile
  • The crest is a flat (or rounded) surface connecting the flanks at the top of the thread grooves, whether internal or external.
  • The crest width depends on the amount of truncation applied to the fundamental triangle, which is defined by the specific thread standard.
Int root and crest

Internal Thread

  • Crest width of 60° standard threads: Fcn=0.25 X P
  • The minor diameter is measured on the crest.
Extr root and crest

External Thread

  • Crest Width of 60° standard threads: frc=0.125 X P
  • The major diameter is measured on the crest.
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