Thread Root Definition
![Thread Root 2 Root Terms](https://www.machiningdoctor.com/wp-content/uploads/2023/05/Root-Terms.png)
- 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.
![Thread Root 3 Int root and crest](https://www.machiningdoctor.com/wp-content/uploads/2022/04/Int-root-and-crest.png)
Internal Thread
- Root Width of 60° standard threads: Frn=0.125 X P
- The major diameter is measured on the root.
![Thread Root 4 Extr root and crest](https://www.machiningdoctor.com/wp-content/uploads/2022/04/Extr-root-and-crest.png)
External Thread
- Root Width of 60° standard threads: Frs=0.25 X P
- The minor diameter is measured on the root.