Definition
API Connection — An API connection is a rotary-shouldered thread standardized by the American Petroleum Institute — such as NC, Regular, Full Hole and Internal Flush — that provides interchangeable, published dimensions and make-up torques for drill string tubulars.
Also known as: API connections, API thread, API rotary connection
What API connections are
An API connection is a rotary-shouldered thread form defined by American Petroleum Institute specifications, principally API Spec 7-1 (and the legacy API Spec 7). Standardization means a pin and box from different manufacturers of the same connection designation will make up correctly and share published thread dimensions, gauging points and recommended make-up torques.
The main API families are NC (Number Connection), Regular (REG), Full Hole (FH) and Internal Flush (IF). Each is a single-shoulder connection identified by size and type, for example NC50 or 6-5/8 REG.
Why standardization matters
- Interchangeability — string components from multiple sources thread together reliably.
- Inspection — connections are gauged to API tolerances during DS-1 or API RP 7G-2 inspection.
- Reference torques — API publishes make-up torque values by connection and OD.
When premium is needed
API connections cover most drilling; higher-torque or gas-tight service may call for proprietary premium or double-shoulder connections instead. We rent drill pipe and drill collars in the common API connections — contact us to match your string.