According to the tooth type, it can be divided into triangular, trapezoidal, rectangular, serrated and circular arc threads;
According to the direction of thread rotation, it can be divided into left-handed and right-handed;
According to the number of spiral lines, it can be divided into single line and multi line;
According to the shape of the thread body, it is divided into cylinder and cone.
Elements of the thread
Thread includes five elements: tooth type, nominal diameter, number of threads, pitch (or lead), and direction of rotation.
1. Tooth shape
In the cross-sectional area passing through the thread axis, the profile shape of the thread is called the tooth profile. There are triangular, trapezoidal, sawtooth, arc and rectangular tooth shapes.
There are major diameters (d, D), intermediate diameters (d2, D2), and minor diameters (d1, D1) for the thread. The nominal diameter is used when representing the thread, and the nominal diameter is the diameter that represents the thread size.
3. Number of lines
The thread formed along a helical line is called a single thread, and the thread formed by two or more helical lines equally spaced along the axial direction is called a multi-thread thread.
4. Pitch and lead
The pitch (p) is the axial distance between two adjacent points on the pitch line.
Lead (ph) is the axial distance between two adjacent teeth on the same spiral line corresponding to two points on the pitch line.
For single thread thread, lead = pitch; for multi thread thread, lead = pitch × number of threads.
The thread screwed in when rotating clockwise is called right-hand thread;
The thread that is screwed in when rotating counterclockwise is called a left-hand thread.