Thread Content
The bolt performance grade designation consists of two digits, which represent the nominal tensile strength value of the bolt material and the yield strength ratio, respectively. 48 is 4.8. For example, a bolt with a performance grade of 4.8 means that: 1. The nominal tensile strength of the bolt material is at the 400 MPa level ； 2. The yield strength ratio of the bolt material is 0.8 ； 3. The nominal yield strength of the bolt material is 400×0.8=320 MPa; it is a high-strength bolt of grade 10.9. After heat treatment, the material achieves the following properties: 1. The nominal tensile strength of the bolt material reaches 1000 MPa ； 2. The yield strength ratio of the bolt material is 0.9 ； 3. The nominal yield strength of the bolt material is 1000×0.9=900 MPa. The performance grade of bolts represents a standard used internationally; bolts with the same performance grade have identical properties, regardless of their material or place of origin. In design, it is sufficient to specify the performance grade alone. The strength grades of 8.8 grade and 10.9 grade refer to the shear stress resistance levels of bolts being 8.8 GPa and 10.9 GPa respectively. For an 8.8 grade bolt, the nominal tensile strength is 800 N/mm2 and the nominal yield strength is 640 N/mm2. Generally, bolts have their strength indicated as “X.Y”; where X*100 represents the tensile strength of the bolt, and X*100*(Y/10) represents its yield strength (since according to the labeling standards, yield strength/tensile strength = Y/10, meaning that Y is the yield-to-tensile strength ratio). For example, in the case of a 4.8 grade bolt, its tensile strength is 400 MPa ； The yield strength is: 400*8/10=320MPa. Additionally: Stainless steel bolts are usually labeled as A4-70, A2-70, etc.; the meaning of these designations is explained separately. Units of measurement: There are mainly two systems for measuring length in the world today. One is the metric system, whose units include meters (m), centimeters (cm), millimeters (mm), etc.; this system is widely used in Europe, China, Japan, and other Southeast Asian countries. The other is the imperial system, whose main unit is the inch; this system is more commonly used in the United States, the United Kingdom, and other European and American countries. 1. Metric system: (decimal) 1 m = 100 cm = 1000 mm. 2. Imperial system: (octal) 1 inch = 8 inches; 1 inch = 25.4 mm. 3/8 inch × 25.4 = 9.52. 3. For products smaller than 1/4 inch, their diameter is indicated by numbers such as 4#, 5#, 6#, 7#, 8#, 10#, 12#.