What is the general rule for using self-locking nuts?

The general rule for using self-locking nuts is that they should not be used at joints that rotate. Self-locking nuts are designed to maintain tightness and resist loosening due to vibration or movement, but in applications where there is continuous rotation, such as on rotating machinery or components, the constant movement can cause the locking mechanism to wear out or become ineffective. In such cases, other types of fastening methods are preferable as they can provide a more reliable connection under conditions of rotation.

While there are various practices regarding the use of self-locking nuts, such as considerations for material compatibility and the potential use of washers, the primary and most critical guideline pertains to their application at non-rotating joints to ensure optimal performance and safety.