What does 8.8 mean on a screw?
As a rule, a layperson does not worry about the marking on a screw that is being used. The screws offered in hardware stores correspond to rather low quality standards, but are sufficient for most purposes in the yard and garden. For special tasks, the mechanic needs to know what the 8.8 on a screw means and how to use it.
How to judge a screw
- For many years after the beginning of industrialization, many manufacturers produced screws with their own characteristics. This meant that only screws from the same manufacturer could be used for repairs. Only in the course of the 2nd During the World War, the western world agreed on a common standardization in order to gain advantages in the war against Nazi Germany.
- In Germany, the standardization all screws comply with DIN EN ISO 898. The first part concerns the screws, while the second part deals with the nuts. Here screws are divided into 10 strength classes according to their properties. These are valid for all screws with a diameter of 5 mm or more.
- The specified strength class, e.g. B. 8.8, determines the purposes for which the screw in question may be used. The information is usually on the screw head, but can also be placed anywhere else if the shape of the screw does not allow otherwise.
What z. B. a 8.8 on one screw means
- The scale of the strength classes begins at 3.6 (the point can also be omitted). The highest class is called 12.9 and designates a screw with the highest achievable strength in industrial production. The tighter the screws are, the more they can be subjected to tensile loads.
- The tensile load is measured in Newtons per mm². The strength class 4.8 has a tensile load limit of 400N / mm², whereas the strength class 12.9 has a limit of 1200N / mm². With an increasing strength class, however, the elasticity of a screw decreases, which means, among other things, that it becomes more sensitive to "overtightening".
- Strength class 8.8 is generally used in industry. These screws are suitable for almost all common applications and have good performance properties. They can be bought both black and rustproof.
- If you come across an underlined number in strength class 10.6 or 12.9, it is a low carbon steel screw Such screws generally will not acted. They serve very special purposes and are of no interest to the normal consumer.
Shear Strength of Screws - Information
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