Here is another style, with a large assortment, a thread restoring kit. I have a Craftsman version of this (older, Made in USA) and it is a quality product. The threaded portion is more like a standard nut or bolt thread but flutes are cut into the threads, similar to taps and dies for dirt and grime removal. They are hardened so that you will strip a thread quite effortlessly, if you use the wrong thread pitch by mistake. Guess how I know.
The thread files are also very useful.