As for the fastener bolt, we all know that it is classified, but the nut is also classified. Do you know whether it is clear? Today, the Chinese standard parts net summarizes the relevant level analysis of the sensible nut. Of course, the nut is screwed together with the bolt for fastening, so how can we make the nut and bolt grade match for better use?

Nut grade analysis:
Nuts can be divided into common, non-standard, (old) national standard, new national standard, American system, British system, German standard, etc. according to different standard numbers of corresponding countries. Hexagon nuts are divided into three types, I type, II type and thin type according to the nominal thickness. Nuts above grade 8 are divided into type I and type II.
The type I hexagon nut is widely used. The type I nut is divided into three grades A, B and C. The Grade A and B nuts are suitable for machines, equipment and structures with small surface roughness and high precision requirements, while the grade C nut is used for machines, equipment or structures with rough surface and low precision requirements. The thickness of the type II hexagon nut is relatively thick, which is often used in the occasions requiring assembly and disassembly.

Common national standards for nuts:
Gb41 type I hex nut - grade C
Gb6170 type I hex nut - grade A and B
Gb6171 type I hex nut fine thread class A and B
Gb6172 hexagon thin nut - grade A and B - Chamfer
Gb6173 hexagon thin nut - fine thread - grade A and B
Gb6174 hex thin nut - grade B - no chamfer
Gb6175 type II hex nut - grade A and B
Gb6176 type II hex nut fine thread class A and B
Gb6177 hexagon flange nut - class A
Gb55 hex thick nut
Gb56 hexagon extra thick nut
Gb1229 large hexagon nut (high strength for steel structure)
The grades of metric bolts are: 4.6; 4.8; 5.8; 6.8; 8.8; 9.8; 10.9; 12.9
The grades of metric nuts are: 4; 5; 6; 8; 10; 12 of which 4; 5 are the strength grades of thin nuts.
Nut a; B; C is equivalent to American G2; G5; G8 performance grade, which is basically consistent with j995!
The thread specification of type I nut is m1.6 ~ M64, and the performance grade is 6; 8; 10; a2-50; A2-70; a4-50; a4-70; Cu2; cu3 and AL4, and the product grade is a and B, and a is used for specifications less than or equal to M16; B is used for specifications greater than M16! (here a; B refers to the accuracy grade);
The thread specification of type II nut is M5 ~ M36, the performance grade is 9 and 12, the product grade is a and B, and a is used for specifications less than or equal to M16; B is used for specifications greater than M16! (here a; B refers to the accuracy grade);
Due to the high requirements for performance grade of type 2, the performance grade of thick bolts with nuts can be divided into more than 10 grades, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc., of which grade 8.8 and above bolts are made of low-carbon alloy steel or medium carbon steel and heat treated (quenched, backfired), commonly known as high-strength bolts, and the rest are commonly known as ordinary bolts.


How to match the grade of bolt and nut? If the grade of bolt is 8.8, what grade of nut should be used?
The grades of metric bolts are: 4.6; 4.8; 5.8; 6.8; 8.8; 9.8; 10.9; 12.9
The grades of metric nuts are: 4; 5; 6; 8; 10; 12 of which 4; 5 are the strength grades of thin nuts.
So: grade 8.8 for bolts and grade 4 for nuts, is that meaningful?
First of all: levels 8.8 and 4 are too unscientific.
In general, the decimal after the bolt grade is the grade of nut. Grade 8.8 bolt is equipped with grade 8 nut, and grade 10.9 bolt is equipped with grade 10 nut.
That is to say, the strength grade of bolt and nut is the same (the strength grade of bolt 8.8 and nut 8 is the same, because the ". 8" after bolt indicates that the yield strength is 80% of the tensile strength). )
However, if the nut is not easy to replace, the bolt is easy to replace, and it can also be changed into bolt 4.8 nut 5.
In some cases, the strength of the nut is a little lower than that of the bolt. The main reason is that the failure of the bolt is usually imperceptible, sometimes sudden, and the failure of the nut is more easily found. Also considered the security aspect. In this way, the service life of the screw is longer than that of the nut when it is used together. In addition, when the fastener is disassembled and replaced, the cost will be cheaper and easier.