What do the numbers on screw heads mean?

The numbers visible on screw heads indicate the strength classes of the screws. They provide information about mechanical properties such as tensile strength, yield strength, and elongation. This is important for determining the load-bearing capacity and durability of fastening materials in various applications.

• Tensile strength: The first digit indicates the minimum tensile strength. For example, a number 8 means a minimum tensile strength of 800 N/mm².
• Yield strength: The number after the decimal point shows the yield strength as a ratio to the tensile strength. An 8.8 screw has a yield strength of 80% of the tensile strength, i.e. 640 N/mm².
• Elongation: Screws without a marking on the head have a minimum elongation at break of 14%, while screws of class 8.8 and above only need to have 12%.

Identifying the strength class of a screw is crucial for selecting the right fastening material, depending on the expected load. A wrong choice can lead to material failure and potential safety issues.