Thread "chasers" are snake oil. They are just screw threads with a big cleanout groove. Like when you make one from a bolt. I use taps and dies to cut thru rust and corrosion. It taps the same thread as the original tap that was used. If you can't do it, use a "chaser". They get stuck on crusty threads just the same as a bolt would. I'm not trying to clean off grease, I do that first with gas, blaster, WD40, carb cleaner, soap or wire wheel. A chaser is BS. A fake tool. Machinists I know use a tap and die to renew threads. I'm not talking about fixing stripped threads. I'm talking about restoration of an old truck. Mostly threads I cant sandblast or wire wheel.
