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What does 4.8 on bolt mean?

Categories: FAQStars: 3StarsVisit: -Release time: 2019-10-31 08:39:00
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What does 4.8 on bolt mean?


There are more than 10 grades of steel structure connecting bolts, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc., among which bolts of 8.8 grade or above are made of low carbon alloy steel or medium carbon steel and have undergone heat treatment (quenching and tempering), commonly known as high-strength bolts, and rest are commonly known as ordinary bolts. Performance grade label of bolt composed of two numbers, which respectively represent nominal tensile strength and flexural strength ratio of bolt material. 


For example: bolt of performance grade 4.8 means 

1. Nominal tensile strength of bolts material up to 400MPa; 

2. Flexion strength ratio of bolt material is 0.8; 

3. Nominal yield strength of bolt material reaches 400×0.8=320MPa; 


Performance grade 10.9 high strength bolt after heat treatment, its material can reach: 

a. Nominal tensile strength reaches 1000MPa; 

b. Flexion strength ratio 0.9;

c. Nominal yield strength up to 1000×0.9=900MPa 


The meaning of bolt performance grade is international general standard, bolt of same performance grade, regardless of difference material and origin, its performance is the same, only choose performance grade on the design.


Strength grade 8.8 and 10.9 magnitude refers to level of shearing stress of bolt is 8.8 GPa and 10.9 GPa. General bolt is used "X.Y" strength, X*100= tensile strength of bolt, X*100* (Y/10) = yield strength (because according to the identification: yield strength/tensile strength =Y/10, namely 0.Yield strength: 400*8/10=320MPa.


Keywords in the article: steel structure connecting bolts
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