Different grades of bolts and nuts

Different grades of bolts and nuts

8.8 and 4.8 are the strength grades of bolts. Generally, Grade 8.8 bolts are made of 45 steel, and 

Grade 4.8 bolts are made of Q235-A, but they are not limited to the above two materials

8.8 means:

The first 8 represents the tensile strength Rm

Rm=8 × 100 N/mm2 =800 N/mm2=800MPa

Second,. 8 is the yield strength ratio of 0.8

Re800*0.8=640MPa

4.8 means

Tensile strength Rm=4 × 100 N/mm2=400 N/mm2=400MPa

Yield strength Re=400 × 0.8=320MPa

The performance grades of bolts are divided into more than 10 grades, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, and 12.9. Bolts of grade 8.8 and above are made of low-carbon alloy steel or medium carbon steel and undergo heat treatment (quenching and tempering), which are collectively referred to as high-strength bolts, and the rest are collectively referred to as ordinary bolts. The bolt performance grade designation consists of two parts of numbers that represent the nominal tensile strength value and yield strength ratio of the bolt material.

Hexagon nuts are divided into three types according to their nominal thickness: Type I, Type II,

 and Thin. Nuts above Grade 8 are classified into Type I and Type II.

Type I hexagon nuts are most widely used. Type I nuts are divided into three grades: A, B, and 

C. Grade A and B nuts are suitable for machines, equipment, and structures with low surface 

roughness and high accuracy requirements, while Grade C nuts are used for machines, equipment,

 or structures with relatively rough surfaces and low accuracy requirements; Type II hexagon nuts 

have a relatively thick thickness and are often used in situations where assembly and disassembly 

are often required.