API Spec 5CT Specification for Casing and Tubing, Eighth Edition, Petroleum and natural gas industries-Steel pipes for use as casing or tubing for wells.

The main steel grade of API 5CT:

• API 5CT J55
• API 5CT K55
• API 5CT N80
• API 5CT L80
• API 5CT P110

Casing pipe end thread type

The International Standard specifies the technical delivery conditions for steel pipes (casing, tubing, plain end casing liners and pup-joints) and accessories. It is applicable to the following connections in accordance with ISO 10422 or API Spec 5B:

- short round thread casing (STC);
- long round thread casing (LC);
- buttress thread casing (BC);
- extreme-line casing (XC);
- non-upset tubing (NU);
- external upset tubing (EU);
- integral joint tubing (IJ).

For such connections, this International Standard specifies the technical delivery conditions for couplings and thread protection.
For pipes covered, the sizes, masses, wall thicknesses, grades and applicable end finishes are defined.
It may also be applied to tubulars with connections not covered by ISO/API standards.