This International Standard specifies requirements for single-lug, counterbored, floating anchor nuts, with a self-locking feature achieved by forming the upper portion out-of-round.
SIS SS-ISO 3224:1987 history
1987SIS SS-ISO 3224:1987 Aerospace - Self-locking, floating, single-lug anchor nuts, with counter- bore, classification 1100 MPa/235 °C