To thread again or anew, especially to pass a thread through the eye of a needle or through the loops of a machine. After the thread broke, she had to rethread the sewing machine to continue her project.
To replace or repair the threads on a screw or bolt. The mechanic had to rethread the bolt to ensure it fit securely in the engine.
(computing) To assign a task or process to a new thread or to create threading anew within a program. The developer had to rethread the routine to prevent the application from freezing.