What is a key requirement for nuts that are not self-locking?

For nuts that are not self-locking, the use of safety wire is a key requirement. This is crucial because non-self-locking nuts do not have an inherent mechanism to prevent them from loosening due to vibration or other forces during operation. Safety wire serves as a secondary means of securing the nut in place, ensuring that it does not back off unintentionally. By threading safety wire through both the nut and a corresponding component, a secure connection is maintained, which is especially important in aviation where mechanical reliability is essential for safety.

The other options may have relevance in certain contexts, but they do not directly address the specific need for securing non-self-locking nuts in operation. For instance, while an anti-corrosive coating may be beneficial for preventing rust and degradation, it does not prevent loosening. Similarly, high-strength materials are important for durability but do not address the issue of potential loosening. Coating with lubricating grease can assist in certain scenarios with thread engagement but is not a requirement to secure nuts effectively.