Summary of bolt thread knowledge

Bolt is a kind of engineering material commonly used in industrial engineering, and the main fastening effect of bolt depends on the bite of thread. I will give you a detailed introduction to the relevant knowledge of the thread, which is worth collecting.

1. Thread type

According to the tooth type, it can be divided into triangular, trapezoidal, rectangular, zigzag and arc threads;

According to the thread direction, 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 parent body, it is divided into cylindrical and conical.

Second, the elements of the thread

A thread consists of five elements: tooth shape, nominal diameter, number of threads, pitch (or lead), and direction of rotation.

1. Tooth type:

On the cross-sectional area through the thread axis, the profile shape of the thread is called the tooth type. There are tooth shapes such as triangle, trapezoid, zigzag, arc and rectangle.

2. Diameter

Threads have major diameters (d, D), middle diameters (d2, D2), and minor diameters (d1, D1). The nominal diameter is used to indicate the thread, and the nominal diameter is the diameter representing the thread size.

The nominal diameter of a common thread is the major diameter.

3. Number of lines

A thread formed along one helix is called a single-line thread, and a thread formed by two or more helixes distributed equidistantly along the axial direction is called a multi-line thread.

4. Pitch and lead

Pitch (p) is the axial distance between two adjacent teeth corresponding to two points on the median diameter line.

Lead (ph) is the axial distance between two adjacent teeth on the same helical line corresponding to two points on the pitch line.

5. Direction of rotation

The thread screwed in when rotating clockwise is called right-handed thread;

The thread that is screwed in when it is turned counterclockwise is called a left-hand thread.