Example: A screw is marked with 12.9.
Nuts are differentiated by three load groups. Each load group has
a special designation system for the strength class assigned, so
that the load group can be clearly identified.
Nuts (1) for screw connections with full load capacity
In a connection with a screw, these nuts (1) must be able to bear
the full pre-load at the yield point.
Nut height above 0.8 d (d = nominal dimension).
Strength class of nut
Strength class of associated
screw
4
3.6, 4.6, 4.8
5
3.6, 4.6, 4.8
5.6, 5.8
6
6.8
8
8.8
9
9.8
10
10.8
12
12.8
Nuts (2) for screw connections with limited load capacity
The preceding "0" indicates that, due to their low height, nuts 2
Fig. 24 in this group are only able to withstand the force of a
screw to a limited extent.
Nut height below 0,8 d (d = nominal dimension).
Nuts (3) for screw connections without specified load capacity
This standard contains strength classes (hardness classes) for
Fig. 24, for which no load values can be specified, e.g.
because of their shape and dimensions, but which can only be
classified by their hardness.
Fig. 23: Identification of screws
Strength classes of metric nuts
Fig. 24: Identification of nuts
General information – Maintenance and repair
BW 900-50
31
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