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Hexagon nut grade and classification

Update:06-09-2019
Summary:

Hex nuts are classified into I type, II type and thin t […]

Hex nuts are classified into I type, II type and thin type according to the nominal thickness. Nuts of class 8 or higher are divided into two types, type 1 and type II.

The type I hex nut is the most widely used, and the type 1 nut is divided into three grades A, B, and C. The grade A and grade B nuts are suitable for machines, equipment, and structures with low surface roughness and high precision. Class C nuts are used on machines, equipment or structures where the surface is rough and the precision is not high. The thickness of the type 2 hex nuts is relatively thick and is often used in applications where assembly and disassembly are often required.

The type 1 nut refers to the ordinary hex nut with the nominal height of the nut m≥0.8D, and its type size should meet the requirements of GB/T6170;
The height of the type 2 nut is higher than that of the type 1 nut, and the type size should conform to GB/T6175. There are two purposes for adding a type 2 nut: one is to obtain a relatively inexpensive nut by increasing the height of the nut.

Because the 8-level 1-type nut of D≤M16 does not need to be heat-treated, in the 8-level nut, only the type 2 nut is used for the specification of D>M16~39.
Obviously, the type 1 nut without heat treatment can not meet the mechanical performance requirements of the 9-stage nut. Another purpose of the Type 2 nut is to obtain a 12-stage nut with better toughness. As the height of the nut increases, the guaranteed stress index can be achieved at a lower quenching and tempering hardness, thus increasing the toughness of the nut.
Nut commonly used national standard GB41 I type hex nut - C grade GB6170 I type hex nut - A, B grade GB6171I hex nut - fine teeth - A, B grade GB6172 hex thin nut - A, B grade - chamfer GB6173 Hexagon thin nut - fine teeth - A, B grade GB6174 hexagonal thin nut - grade B - no chamfer GB6175II type hex nut - A, B grade GB6176II type hex nut - fine teeth - A, B grade GB6177 hexagon method Blue nut - Class A GB56 hex thick nut GB1229 large hex nut (high strength for steel structure) Bolt coarse and fine tooth usage; (1) Fine thread thread is good for anti-vibration, easy to adjust the gap, but the lock The force is worse than the coarse teeth. It is suitable for the place where the gap or torque should be adjusted. (2) The self-locking ability of the coarse thread is worse than that of the fine tooth, but the locking force is larger than the fine tooth. Generally, there is no special requirement for the coarse thread. Thread thread: directly follow the thread diameter after M, without marking the pitch, labeling and not marking the pitch, which is the difference between the ordinary fine thread and the ordinary coarse thread. The grade of the metric bolt is: 4.6; 4.8; 5.8; 6.8; 8.8; 9.8; 10.9; 12.9.
The grade of the metric nut is: 4; 5; 6; 8; 10; 12 where 4; 5 is the strength grade of the thin nut.

You said that the nut A; B; C level is equivalent to the US G2; G5; G8 performance level, J995 stipulates that the performance level between the two is basically the same!
Type 1 nut thread specifications are M1.6~M64 performance grade is
6;8;10;A2-50;A2-70;A4-50;A4-70;CU2; CU3 and AL4, product grades A and B, Class A for specifications less than or equal to M16; Class B For specifications larger than M16! (A here; B refers to the accuracy level)
Type 2 nut thread size is M5~M36, performance grade is 9 and 12 grades, product grade is grade A and grade B, grade A is used for specifications less than or equal to M16; grade B is used for specifications larger than M16! (A here; B refers to the accuracy level)
Due to the high performance level of Type 2, the thickness of the nut is thicker. The performance grade of the bolt is divided into more than 10 grades of 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, among which the bolt material of grade 8.8 and above. It is a low-carbon alloy steel or medium-carbon steel and is heat-treated (quenched and tempered). It is called high-strength bolts, and the rest is called ordinary bolts.
 
The bolt performance grade label is composed of two parts, which represent the nominal tensile strength value and the yield ratio of the bolt material. For example, a bolt with a performance class of 4.6 has the following meaning: Bolts with a performance class of 4.6, meaning
1. The nominal tensile strength of bolt material is up to 400MPa; 2. The yield ratio of bolt material is 0.6;
3. The nominal yield strength of bolt material is up to 400×0.6=240MPa
The performance grade 10.9 high-strength bolt, after the material is heat-treated, can reach 1. The nominal tensile strength of the bolt material reaches 1000MPa; 2. The yield ratio of the bolt material is 0.9;
3. The nominal yield strength of the bolt material is 1000×0.9=900MPa
The meaning of the bolt performance grade is the international standard. The bolts of the same performance grade have the same performance regardless of the difference between the material and the place of origin. Only the performance grade can be selected in the design.

 

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