What do the 4.8 and 8.8 on the standard part screws mean?

In the industry, we can see a lot of products, screws are one of the most common things, because in various industries, will see, the use of places is also particularly widespread, screw parts is one of them, then the standard screws on the 4.8, 8.8 means what?

  Structural connection bolt performance grade 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9 and more than 10 grades, of which 8.8 grade and above bolts material for low-carbon alloy steel or medium carbon steel and heat treatment (quenching, tempering), commonly known as high-strength bolts, the rest are commonly known as ordinary screws. 

  The bolt performance grade mark has two parts of numbers, which indicate the nominal tensile strength value of the bolt material and the flexural strength ratio.

  Nominal tensile strength of bolt material up to 400MPa grade

  The bolt material has a yield strength ratio of 0.8

  Nominal yield strength of bolt material up to 400×0.8=320MPa grade 

  Performance grade 10.9 high-strength bolts, whose materials are heat-treated, can achieve.

  Nominal tensile strength of bolt material up to 1000 MPa grade

  The bolt material has a flexural strength ratio of 0.9

  Nominal yield strength of bolt material up to 1000×0.9=900MPa grade 

  The meaning of the bolt performance level is the international standard, the same performance level of the bolt, regardless of the difference between its material and origin, its performance is the same, the design of only the performance level can be selected.

  The above is the standard part of the screw on the 4.8, 8.8 means what, in the case you understand, as long as a good understanding of the situation, you can know, after understanding, will have a more different insight, or more understanding of it.