A threading tap often takes a cut of the existing threads. Not a deal breaker, just make sure you have the right tap.

A thread cleaning tap is slightly undersized and should be just large enough to take any dirt out.

If your deepening the threads, you need the bottoming tap. Often times the bottoming threads just need cleaning.

Kevin

87 Turbo Intercooled Raider, roller cam, torsen rear diff, LSD front diff, lockup auto with modified converter, V6 brakes, low transfer case gears...