What are the elements of threaded fasteners?

Threaded fasteners use a pair of internal and external threads to connect and fasten some parts. They all have a similar characteristic, which is the thread profile, which is used to determine the geometry of the thread, but only the core When the elements are the same, the internal and external threads can be screwed together. What are the elements of threaded fasteners? There are mainly the following six core elements.

1. Working height: the distance between the overlapping part of the two-phase matching thread profile in the direction perpendicular to the thread axis, etc. The nominal diameter of the thread is the nominal diameter of the pipe thread, except for the pipe inner diameter, and the outside diameter is the nominal diameter. The thread has been standardized, and there are metric (metric) and imperial systems. The international standard adopts the metric system, and China also adopts the metric system.

2. Lead: The axial distance between two adjacent teeth on the pitch line corresponding to two points is called the pitch. On the same spiral line, the axial distance between two adjacent teeth corresponding to two points on the median diameter line is called the lead. The relationship between the number of lines n, the pitch P, and the lead S is: Su003dnP.

3. Rotation direction: Seen along the axis, the thread that rotates clockwise becomes right-handed thread, and the thread that rotates counterclockwise is called left-handed thread. (Guide: Application of cold deformation performance of three types of fasteners)

4. Major diameter, minor diameter and intermediate diameter: Major diameter refers to the diameter of an imaginary cylindrical or tapered surface that coincides with the top of the external thread and the bottom of the internal thread. The major diameter of the external thread is represented by d. The major diameter of the internal thread is represented by D. The minor diameter refers to the diameter of an imaginary cylindrical or tapered surface that coincides with the root of the external thread and the crest of the internal thread. The minor diameter of the external thread is represented by d1, and the minor diameter of the internal thread is represented by D1. For example, a car screw, between the major diameter and the minor diameter, imagine a cylindrical surface (or cone), in its axial section, the width of the tooth on the plain line is equal to the width of the groove, then the diameter of the imaginary cylindrical surface is called Pitch diameter, represented by d2 (or D2).

5. Tooth shape: On the section passing through the thread axis, the profile shape of the thread is called the tooth shape. The angle between two adjacent flanks is called the profile angle. Commonly used common thread has a triangular profile with a profile angle of 60°.

6. Number of threads: The number of spiral threads forming a thread is called the number of threads. There are single-thread and multi-thread threads. The multi-thread threads are evenly distributed in the section perpendicular to the axis.

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