Many of us have experienced the pain of cross-threading; careful as we try to be, sometimes things are just so unwieldy that cross-threading is inevitable. With these thread-restoring files you may be able to restore those damaged or worn — external — threads.
We assume you just run the file around the threads repeatedly — tedious but manageable. I’d be interested to try them out; I’ve abandoned a number of fun junk projects because of damaged threads.
The files in the set pictured above, from Cooper Hand Tools, each fit multiple thread sizes: One is metric, two are standard (odd and even?), and one works for pipe. A single file runs up to $15, and the set runs $40 on Amazon.