What are the elements of bolt fasteners

Updated:12-08-2020
Summary:

Bolt fasteners use a pair of inner and outer bolts to c […]

Bolt fasteners use a pair of inner and outer bolts to connect and fasten some parts. They all have a similar characteristic, which is the thread shape of the bolt, which is used to determine the geometric shape of the bolt, but only the core When the elements are the same, the inner and outer bolts can be screwed together. What are the elements of bolt fasteners? There are mainly the following six core elements.

 

1. Working height: the distance between the overlapping part of the two-phase matching bolt thread in the direction perpendicular to the bolt axis. The nominal diameter of the bolts is the nominal diameter of the pipe bolts except the pipe inner diameter, and the outside diameter is the nominal diameter. The bolts have been standardized and are available in 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 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: S=n·P.

 

3. Rotation direction: Seen along the axis, the bolt that rotates clockwise becomes right-handed bolt, and the bolt that rotates counterclockwise is called left-handed bolt.

4. Major diameter, minor diameter and medium diameter: Major diameter refers to the diameter of an imaginary cylindrical or tapered surface that coincides with the top of the external bolt and the bottom of the internal thread. The major diameter of the external thread is represented by d, and the diameter of the internal thread The major diameter is represented by D. Minor diameter refers to the diameter of an imaginary cylindrical or tapered surface that coincides with the bottom 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, imagines 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 the two adjacent flanks is called the profile angle. Commonly used common thread has a triangular profile with a profile angle of 60°.

 

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

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