Which of the following is a sign that a Jo-bolt fastener needs to be replaced?

A Jo-bolt fastener that spins indicates that it is no longer properly engaging with the components it is intended to fasten. This spinning could suggest that the threads are stripped or damaged, preventing adequate tightening and compromising the integrity of the connection. When a fastener cannot achieve the required torque, it may lead to loosening or failure of the joint under load, which is critical in aerospace applications where structural integrity is paramount. Therefore, a spinning fastener is a clear indicator that it should be replaced to ensure safety and reliability.

While signs such as rust, being painted over, or being too long might imply potential issues, they do not directly indicate a loss of functional engagement as a spinning fastener does. Rust could be a cosmetic issue or lead to structural problems, but it doesn't immediately affect the fastening capability. Being painted over may complicate inspection or maintenance but does not inherently render a fastener ineffective. Lastly, a fastener being too long may not affect its ability to secure components, assuming it is still properly threaded and engaging correctly.