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WHAT DOES THE MEAN OF 4.8 ON BOLTS ?

Bolts are widely used in machine manufacturing, steel structure connection, assembly of machined parts and other industry lines.

The bolts grade types:

The performance grades of bolts for steel structure connection are 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9 and 12.9. The bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel and are heat treated (quenched and tempered). They are commonly referred to as high strength bolts, and the others are commonly referred to as ordinary bolts. The grade label of bolt performance consists of two parts, which represent the nominal tensile strength and yield strength ratio of bolt material. 48 is 4.8.
bolts
bolts

Bolts performance grade:

FOR EXAMPLE, A BOLT WITH A PERFORMANCE GRADE OF 4.8 MEANS:

  1. The nominal tensile strength of bolt material is 400 MPa.
  2. The yield-strength ratio of bolt material is 0.8.
  3. The nominal yield strength of bolt material is 400 x 0.8=320 MPa.

THE MATERIAL OF HIGH STRENGTH BOLT OF GRADE 10.9 AFTER HEAT TREATMENT CAN REACH:

  1. The nominal tensile strength of bolt material reaches 1000MPa grade.
  2. The yield-strength ratio of bolt material is 0.9.
  3. The nominal yield strength of bolt material reaches 1000 x 0.9=900MPa grade.
The meaning of bolt performance grade is an international standard. Bolts with the same performance grade have the same performance regardless of their material and origin. Only performance grade can be selected in design.

Bolts strength grade:

Strength grades 8.8 and 10.9 refer to the shear stress grades of bolts which are 8.8 GPa and 10.9 GPa 8.8 nominal tensile strength 800N/MM2 nominal yield strength 640N/MM2. Generally, bolts are expressed as strength by “X.Y”. X100 = the tensile strength of the bolt, X100* (Y/10) = the yield strength of the bolt (because the yield strength/tensile strength = Y/10, i.e. 0.Y is the yield strength ratio) as specified in the label. For grade 4.8, the tensile strength of the bolt is 400 MPa and the yield strength is 400*8/10=320 MPa.
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