04-03-2013, 01:19 AM
I'd recommend a spiral point tap rather than a spiral flute tap. Spiral flute taps tend to "unwind" and grow larger as they get tight, taking even a deeper cut. This is an advantage when power tapping, because when you reverse them, the "relax" and don't drag very much on the way out. But you're hand tapping. Spiral point taps are a bit stronger, but you must allow for the fact that they throw the chip forward, so either you must have enough hole dept to allow for the chip, or back out frequently to prevent the chip from binding up.