What does 48 on the bolt represent?
Thread Content
The performance grades of bolts used for steel structure connections include more than 10 grades such as 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 have undergone heat treatment (quenching and tempering); they are commonly referred to as high-strength bolts, while the rest are known as ordinary bolts. 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-to-tensile 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. The nominal tensile strength for 8.8 grade is 800 N/mm2, while the nominal yield strength is 640 N/mm2. Generally, bolts have their strength indicated as “X.Y”; where X*100 represents the bolt’s tensile strength, and X*100*(Y/10) represents its yield strength (as per the standard, 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 designated 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#.
The “4.8” on the bolt indicates its performance grade. The specific explanation is as follows: - The first number, “4”, represents the nominal tensile strength value of the bolt material, which indicates the bolt’s resistance to tension. In this case, “4” indicates that the tensile strength of the bolt is 400 MPa (megapascals). - The second digit, “8”, represents the yield strength ratio of the bolt material, that is, the ratio of the bolt’s yield strength to its tensile strength. In this case, \"8\" indicates that the yield strength ratio of the bolt is 0.8 (80%). Therefore, for bolts of grade “4.8”: 1. The nominal tensile strength of the bolt is 400 MPa. 2. The nominal yield strength of the bolt is 400 MPa * 0.8 = 320 MPa. These performance grades are internationally recognized standards; regardless of differences in material or origin, bolts with the same performance grade possess identical properties. In terms of design, it is only necessary to select the appropriate performance level. Additionally, the strength grade of bolts can also be expressed as “8.8” or “10.9”; here, “8.8” indicates that the bolt’s shear stress resistance is 8.8 GPa, while “10.9” means that the bolt’s shear stress resistance is 10.9 GPa. These values indicate the strength grade of the bolt; generally, bolts with a higher grade possess greater strength. Finally, regarding units of length, the metric system uses units such as meters, centimeters, and millimeters, while the imperial system uses inches. For example, 1 inch is equal to 25.4 millimeters. Numbers (#) are usually used to indicate products of different sizes, such as the diameter of bolts. .