Definition
NC Connection — An NC (Number Connection) is a family of API rotary-shouldered connections identified by a two-digit number equal to the pin's pitch diameter in tenths of an inch, providing standardized, interchangeable threads for drill pipe and drill collars.
Also known as: NC connections, Number Connection, NC thread, NC50, NC38, NC46
What an NC connection is
The NC (Number Connection) family is the most widely used group of API rotary-shouldered connections. The number in the designation — for example NC38, NC46 or NC50 — is the pin thread pitch diameter measured at the gauge point, expressed in tenths of an inch (NC50 ≈ 5.042 in). All NC connections share the same V-0.038R thread form and a 2 in taper per foot.
NC connections were developed to unify several older thread series, and today cover most drill pipe and drill collar sizes. NC50, for instance, is the standard connection on 5 in drill pipe.
Key facts
- Naming — the number is pitch diameter in tenths of an inch, not the pipe size.
- Interchange — some NC connections are dimensionally interchangeable with older Full Hole or Internal Flush connections (e.g., NC50 with 5 IF).
- Single shoulder — NC is a single-shouldered connection; high-torque work may use double-shoulder premium threads instead.
Renting NC-connection tubulars
NC connections dominate rental drill string inventory. We stock drill pipe and drill collars in common NC sizes, gauged to API tolerance — contact us to confirm the NC connection your string needs.