Threaded connection means that the end of the pipe is processed into an outer honeycomb pattern according to the specified thread standard and screwed together with the pipe fitting with internal thread. Because the shape of the thread is divided into cylindrical pipe thread and tapered pipe thread. As the external and internal threads processed on the pipes and fittings are tapered threads or cylindrical threads, the form of the threaded interface is different, and the effect is different.

(1) The cylindrical thread is connected to the cylindrical thread. The external thread of the pipe end and the internal thread of the pipe fitting are both cylindrical pipe threads. Due to manufacturing tolerances, the diameter of the external thread is smaller than the diameter of the internal thread. Cylindrical thread connection is only the crimping between all thread tooth surfaces, the crimping area is large, the strength is high, but the pressure on the crimping surface is small and the tightness is poor.

(2) Conical thread is connected to cylindrical thread. The external thread of the pipe end is the connection between the taper thread and the internal thread of the pipe fitting is the connection between the cylindrical thread. Since only the base surface of the tapered thread is equal to the diameter of the cylindrical thread, the connection between all threads has the pressure on the contact surface of the tooth surface. It also has a pressing effect on the base surface, and the strength and tightness of the threaded connection are good. It is the main interface form of the pipe threaded connection.

(3) Taper thread is connected to taper thread. The external thread of the pipe end and the internal thread of the pipe fittings are both tapered pipe threads. With the tightening of the connectors, the connection between the threads includes both crimping between all tooth surfaces and compression on all tooth surfaces. The strength and tightness of the interface are good, but due to the difficulty of internal thread processing, this interface form is used in medium and high-pressure pipeline projects that require high interface strength and tightness or in oil and gas pipelines with specific requirements.