When threading a self-locking nut on a bolt, what indicates the nut should be rejected?

A self-locking nut is designed to maintain its position on a bolt due to friction created by its internal threads. When a self-locking nut can be easily threaded onto a bolt with just your fingers, it suggests that it may not be accomplishing its primary function of locking in place effectively. This ease of threading could indicate that the locking mechanism has worn out or that the nut does not fit correctly on the bolt.

A nut that threads too easily might not provide the necessary resistance to vibration and movement, which is critical in maintaining the integrity of the assembly. Self-locking nuts are intended to have a certain level of interference with the bolt to ensure they stay secure, and if this interference is absent, it compromises the safety and reliability of the mechanical connection.

In contrast, a nut that requires a wrench for complete threading may still provide adequate locking function, and a clicking sound could suggest normal operation within some contexts, depending on the nature of the threads. Visible wear on the threads would also be a cause for concern, but ease of threading is a definitive indicator that the nut should be rejected for safety reasons.