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Thread Root Definition

Root Terms
  • The root is a flat (or rounded) surface connecting the flanks at the bottom of the thread grooves, whether internal or external.
  • The root width depends on the amount of tip truncation, which is defined by the specific thread standard.
Int root and crest

Internal Thread

  • Root Width of 60° standard threads: Frn=0.125 X P
  • The major diameter is measured on the root.
Extr root and crest

External Thread

  • Root Width of 60° standard threads: Frs=0.25 X P
  • The minor diameter is measured on the root.
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