A spiral point tap is for a hole that is completely through the workpiece. This is because as the tap cuts the thread the swarf is being pushed forward away from the cutting edge and eventually through the bottom of the hole which then breaks the swarf from the job allowing the tap to reverse and safely return to its starting position.
A spiral flute tap is for a hole that does not break through the workpiece (blind hole). These taps are designed for the swarf to travel up the spiral form of the tap and out through the top of the hole. Once the tap stops and starts to run in reverse the swarf is broken from the job allowing the tap to return to its starting position.
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