National Course Thread (N.C) is the screw thread type formerly known as what?

• A. Screw thread of common use formerly known as US standard thread.
• B. A fine threading standard for precision work.
• C. A thread standard for pipes and fittings.
• D. A metric thread standard used worldwide.

Answer: (A)

National Coarse threads are the coarse-form version of the United States thread standard. This type was historically referred to as the US standard thread before the Unified Thread Standard (UNC/UNF) system was adopted. So, the coarse thread form known as National Coarse corresponds to what was once called the US standard thread—the broad, common threading used for general fasteners.

The other options describe different standards: a fine thread for precision work corresponds to Unified Fine threads, pipe threads are different standards like NPT, and metric threads are the M-series.