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The metric thread is used for threaded rods, screws and nuts for fastening non-positive connections.

The diameter is given in millimetres and marked with an "M", for example M8, M10 or M30.

It is a right-hand thread.

### Strength classes

Class 4.6
Tensile strength of 400 N/mm²
Yield strength of 240 N/mm²

Class 4.8
Tensile strength of 400 N/mm²
Yield strength of 320 N/mm²

Class 8.8
Tensile strength of 800 N/mm²
Yield strength of 640 N/mm²

### Calculation of tensile/yield strength

The tensile strength of threaded rods is the determining force per area that a threaded rod, threaded bolt, threaded bar or threaded piece can absorb as the maximum load in relation to its cross-section. This is referred to in strength theory as the permissible stress (tensile strength) in the same way as for screws and nuts. It is given in N/mm².

To differentiate the tensile strength of threaded rods, metric threaded rods and threaded bars made of carbon steel are divided into strength classes (grades) according to their material properties, just like steel screws.

The marking of the strength class of a metric threaded rod consists of two numbers separated by a dot. The left number (4, 5, 8, 10 or 12) corresponds to 1/100 of the nominal tensile strength in N/mm², the right number (6, 8 or 9) indicates ten times the ratio of the lower yield strength to the nominal tensile strength:

Calculation example: class 4.6

 Tensile strength: Relevant: Left number (4) Operation: Left number (4)*factor 100 Result: 4*100 = 400 N/mm²

 Yield strength: Relevant: Left number (4) & Right number (6) Operation: Left number (4)*Right number (6)*10 Result: 4*6*10 = 240 N/mm²

The yield strength or elongation is the maximum load that should be taken into account when calculating a construction statics!