On the section passing through the thread axis, the outline shape of the thread is called a thread profile. It has triangle type, ladder type, sawtooth type and square type, etc. Different thread tooth types have different uses and are represented by different codes.
1. Ordinary thread (M)
Ordinary thread is the most commonly used connection thread. The tooth profile is triangular, the profile angle is 60 °, and the thread feature code is M. Ordinary threads are divided into two types, coarse teeth and fine teeth, which have the same code.
Generally, coarse threads are used for the connection. When the diameter of the threads is the same, the pitch and profile height of the fine threads are smaller than that of the coarse teeth. Therefore, the fine threads are suitable for the connection of thin-walled parts.
2. Inch pipe threads (G, R, Rp, Rc)
Pipe threads are mainly used to connect pipes. The tooth profile is triangular and the profile angle is 55 °. There are two types of pipe threads:
1) Non-thread-sealed pipe thread The thread type is G, and the internal and external threads are cylindrical threads. The internal and external threads are screwed without sealing ability. They are often used for connections in pipelines that do not require sealing.
2) Thread-sealed pipe threads There are 3 types of thread codes: tapered external threads are R; tapered internal threads (taper 1:16) are Rc; cylindrical internal threads are Rp. This thread can be a conical internal thread and a conical external thread. It can also be a cylindrical internal thread and a conical external thread. The internal and external threads are sealed after being screwed together. They are often used for water pipes, gas pipes, and lubricating oil pipes.
3. Ladder thread (Tr)
The trapezoidal thread is a commonly used transmission thread. The tooth profile is an isosceles trapezoid, the profile angle is 30 °, and the thread type code is Tr.
4. Serrated thread (B)
The zigzag thread is a unidirectionally stressed transmission thread. The tooth profile is an unequal waist trapezoid. The profile angle on one side is 30 °, and the profile angle on the other side is 3 °.