Screw Thread Nomenclature

Screw Thread Nomenclature

Screw Thread Nomenclature - The standard screw thread nomenclature is illustrated. The crests of external threads may be either rounded or flat. The root usually is made rounded to minimize stress concentration at this critical area. The internal thread has a flat crest in order to mate with either a rounded or V root of the external thread.

A small round is used at the root to provide clearance for the flat crest of the external thread. While all elements of the thread form are based on the pitch diameter, screw thread sizes are expressed in terms of the outside, or major, diameter and the number of threads per inch of length.