Thread Root

• 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.

Internal Thread

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

External Thread

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