What is a Major Diameter of a Thread?

The major diameter of a thread is the diameter of an imaginary cylinder that touches the largest diameter of a thread. The nominal value of the major diameter equals the nominal thread size. Extremal Threads: The major diameter is measured on the crest of the thread. Internal Threads: The major diameter is measured on the root of the thread. Learn More: https://www.machiningdoctor.com/glossary/major-diameter/