ball end mills. the teeth are called flutes. four flutes is for steel and two are made for soft stuff some types of aluminum. and yes you need to be rigth on center .the ball end mill is the one you want this will drill a hole .spray penetrant will burn off. i like the wax. it wick it self in the threads. i have tig weld a tower up with weld .the tig dose this very good and you can control how much weld you put down. and the heat it makes when welding helps to burn the junk out like sealer and lock tite and grab the tower with vise-grip you can weld a nut to it but the zinc plated nut s some times weld like crap . tower works the best for me