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Thread Crest Definition

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 tip truncation, 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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