More than anyone would care to admit, a stripped thread has reared its ugly head and put a damper on any repair, project, you name it. Do not despair. There's a very good chance you can repair the thread rather than throwing the baby out with the bath water. Just as there are various degrees of stripped threads, there are various ways to repair them.
Working from bad to worse, the thread chaser is a tool that works well when the thread is stripped due to being dirty and/or clogged with metal. When faced with this sort of strippage, it's best to clean out the threads rather than create new ones. The tool for the job is a thread stripper, which is a kind of die. It goes inside the bolt hole, and as you turn it, it cleans out the threads without removing any additional metal.
Thread inserts are necessary when the threads are just a bit too far gone for a thread chaser to have any worthwhile effect. To take advantage of the thread insert, use a drill to remove the existing threads, then insert the thread insert. More than one kind of thread insert kit is available at building supply stores or automotive supply stores. FYI: according to Auto Media, some engine builders supplement the bolt holes in their aluminum engines with steel thread inserts.
When a bolt or screw's threads become damaged, it's possible to repair them in the same manner as the interior threads. In this case, the thread chaser will go over the threads of the bolt or screw, rather than inside the hole. Like the thread chaser for interior threads, it will clean the threads rather than make new ones.