This International Standard specifies requirements for single-lug, counterbored, fixed anchor nuts, with a self-locking feature achieved by forming the upper portion out-of-round.
SIS SS-ISO 3168:1988 history
1988SIS SS-ISO 3168:1988 Aerospace - Self-locking, fixed, single- lug anchor nuts with counterbore, classification 1100 MPa/235 °C