When a tap or die gets dull enough to stop cutting clean threads in a previously unthreaded application, rather than discard it, I set it up in a lathe and use a tool post grinder to take a few thousandths off the top of the thread- - - -internal or external. Now I've got a chaser that isn't going to create an over or undersize when I use it to clean up a dirty or damaged thread. I also give those modified taps and dies a dunk in my gun-bluing tank. That way I can't mistake a chaser for a threading tool, tap or die. The black ones are the chasers!
Jerry
