This is a resource to address an assembly of common questions related to Metric Locknuts.  More than Imperial Locknuts, Metrics can be a challenge to understand due to their limited use and updating activity among the various consensus standards organizations.

METRIC LOCKNUT TERMS

• Class – is determined by the proof load strength of the nut;

• Grade – is typically applied to nut diameters, Grade A ≤ M16, Grade B > M16.
• Style – is typically applied to the ratio of nut diameter to nut thickness, Style 1 = D/.9, Style 2 = D/1.
• Type - is typically applied to …


EVOLUTION OF LOCKNUT SPECIFICATIONS

DIN 980 – replaced by DIN EN ISO 7042 (several changes to across flats)
DIN 985 – replaced by ISO 10511 & ISO 10513
DIN 6923 – replaced by ISO 4161
DIN 6925 – replaced by DIN EN ISO 7042 (fine thread to ISO 10513)
DIN 6926 – replaced by ISO 7043
DIN 6927 – replaced by ISO 7044 & DIN EN 1664 (nut height increased across all diameters)

 
NON-PREFERRED DIAMETERS AND ACROSS FLATS

According to ISO/TC 2, these are the Across Flats dimensions to be phased out;
M10 – 15 & 17
M12 – 19
M14 – 22

According to ISO/TC 2, these are the Diameters to be phased out;
M3.5, M14, M18, M22, M27, M33, M39, M45, M52, M60