scope:

This standard specifies the characteristics of two lug, counterbored, floating anchor nuts, with a self-locking feature achieved by forming the upper portion out-of-round, the dimensions of which are in conformity with ISO 3209.
These nuts are intended for use in aircraft assemblies, in which the fasteners are mainly subjected to shear loads. The counterbore of nuts with thread diameter equal to or greater than 4 mm is deep enough to accommodate a bolt shank in excess of assembly thickness, as well as the incomplete threads.
The 3 mm diameter nut has no counterbore.
They are intended to be used with threaded parts of 1 100 MPa 1) tensile strength classification.
The cadmium plating restricts the application to temperatures not exceeding 235 °C.