Bob La Londe wrote:

Spiral taps conveyor the chips up flutes on the tap and back out the
top of the hole and are suitable for blind hole tapping.

Here are my questions. Should you only use them as described above?
Is there any reason not to use a spiral tap for both through holes and
blind holes? Obviously the gun tap would have a problem in blind
holes if tapping to depth.
Spiral FLUTE taps are what you are talking about. They look like twist
drills with threads in them, and bring the chips up the same way a drill
bit does. There are different from spiral POINT taps.

My experience with spiral flute taps is they are great for shallow blind
holes or through holes in thin material. They don't work well on DEEP
blind holes, like deeper than 5X diameter or so. The chips eventually
bind the tap. Much better to drill deeper and use a gun tap for the
deep holes. A spiral point tap also pushes the chips ahead.

Jon