If a fiber or nylon insert-type, self-locking nut can be easily threaded on with fingers, what should be done?

When a fiber or nylon insert-type self-locking nut can be easily threaded on with fingers, it indicates that the locking mechanism is not functioning as intended, which can compromise the integrity of the connection. Self-locking nuts are designed to maintain tension and resist loosening due to vibrations and other forces. The fact that it can be easily threaded suggests that the insert may have worn out or become damaged.

In such cases, lubricating the nut and reinstalling it is pertinent because it ensures that the threads will have proper engagement, which might help to establish a better fit, at least temporarily. This approach allows for a better assessment of whether the nut can still provide adequate locking under load before deciding to replace it entirely. However, this is typically a temporary measure; if issues persist, swapping the nut for a new one is the safest long-term solution to ensure reliability in the assembly.

Using it for temporary fittings or continuing to use it as is could lead to potential failure, and simply rejecting it without further evaluation might overlook a solution that allows for safe continued use in non-critical applications. Therefore, lubricating and reinstalling offers a balance of caution while still allowing for functional use until a definitive solution is applied.