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Basic Knowledge Of Threading Essential For Programming

Dec 28, 2019

Variety of threads

According to the tooth shape, it can be divided into triangle, trapezoid, rectangle, zigzag and arc thread;

According to the direction of thread rotation, it can be divided into left-handed and right-handed;

It can be divided into single line and multi-line according to the number of spiral lines;

According to the shape of the thread body, it is divided into cylindrical and cone.

Elements of the thread

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

Tooth shape

In the area of the cross section passing through the thread axis, the contour shape of the thread is called a tooth profile. There are triangular, trapezoidal, zigzag, arc and rectangular teeth.


Threads have large diameters (d, D), middle diameters (d2, D2), and small diameters (d1, D1). When the thread is indicated, the nominal diameter is used, and the nominal diameter is the diameter representing the thread size.

3. Number of lines

A thread formed along a spiral line is called a single-thread thread, and a thread composed of two or more spiral wires that are equally spaced in 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 median line.

The lead (ph) is the axial distance between two points on the middle diameter line between adjacent teeth on the same spiral.

For single-threaded threads, lead = pitch; for multi-threaded threads, lead = pitch × number of lines.

5. Rotation

The thread that is screwed in when turning clockwise is called the right-hand thread;

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