The structure of the tubing coupling is: the end of the tubing and the inner wall of the coupling are connected by a tapered thread, and the end of the coupling body and the tubing are connected by a flat thread with the same thread and pitch. It has the characteristics of relieving the stress concentration at the root of the external thread of the tubing connected by a single taper thread, is not easy to cause fatigue and fracture, and the connection effect is good. Effectively prevent the occurrence of breakage accidents of oil well tubing strings.
Couplings are divided into tubing couplings and casing couplings. The commonly used steel grades are J55, K55, N80, L80, P110, etc.