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Types And Elements Of Threads

Nov 27, 2019

Thread is one of the common geometric features in mechanical engineering and is widely used. There are many thread processing techniques, such as rolling and thread rolling based on plastic deformation, turning, milling, tapping and sleeve threading, thread grinding, thread grinding, etc. based on cutting processing.


First, the type of thread


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.


Second, the 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.


Diameter


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


3. Number of lines


A thread formed along a spiral line is called a single-thread thread, and a thread formed by two or more spiral lines 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.