Quote Originally Posted by TerpnGator View Post
Actually John, tools marketed and sold as "thread chasers" ARE JUST REGULAR TAPS. Most, if not all, are cheap, normal carbon steel and most with only 2 flutes. In fact, the only advantage to using a carbon steel tap is if it does break it is much easier to drill out.

Nobody makes an "undersized" tap to use as a thread chaser. This machinist friend of mine actually had a tool that he made to chase threads in a project that he worked on. It was no more than a hardened steel bolt that had a sharp troth cut into the length of the threads.

If you want to clean up your threads, lube your tap well and slowly run it in. A 3/8 tap WON'T cut new threads unless you cross thread it in. It will cut 3/8" threads just like new.
I emailed a friend who has been a machinist most of his life. His comment was:
"Interesting. I had never heard of a tap called a thread chaser. Used what was available starting-bottoming. I have also taken a bolt and ground a slot with a slight "cutting" edge to clean the threads."