Stories you should know about bolts and threads

1. Bolts are divided into ordinary connecting bolts and connecting bolts for reaming holes according to the way of stress during connection. Bolts are divided into head shapes: hexagonal head, round head, square head, countersunk head and so on.

2. The performance level of bolts is an international standard. The performance of bolts with the same performance level is the same, so you only need to select the corresponding performance level when choosing.

Marking of performance level

The bolt performance grade is 8.8 as the demarcation point. The lower part is generally called ordinary bolt, and the upper part (including 8.8) is generally called high strength bolt. The performance grade label consists of two parts, which respectively represent one percent of the tensile strength of the bolt material and the ratio of the yield strength to the tensile strength. For example, if the bolt performance level is ab, it means: 1. The tensile strength of the bolt material is (a100) MPa; 2. The ratio of the yield strength of the bolt material to the tensile strength is 0.b; 3. The yield strength of the bolt material The value is (a1000.b) MPa.

3, basic knowledge of thread

Threads are continuous protrusions on the surface of a cylinder (or cone) along the spiral line with a prescribed tooth profile. The threads are generally divided into two categories: (Guide: One-time nut high-speed cold heading)

External thread: thread on the outer surface of a cylinder (or cone).

Internal thread: thread on the inner surface of a cylinder (or cone).

Internal thread processing method

External thread processing method

Thread major diameter, minor diameter, middle diameter, tooth crest, tooth bottom:

The diameter of an imaginary cylinder (or cone) tangent to the top of the external thread or the bottom of the internal thread is called the major diameter, and the diameter of the imaginary cylinder tangent to the bottom of the external thread or the top of the internal thread is called the minor diameter. The diameter of the imaginary cylinder where the bus bar passes through the grooves and protrusions on the tooth profile is equal in width is called the pitch diameter.

Threaded teeth display

Pitch and lead:

Pitch (p) is the axial distance between two adjacent points on the pitch line.

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

For single thread thread, lead u003d pitch; for multi thread thread, lead u003d number of thread pitch.

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