Plug taps have three to five threads chamfered, to cut threads in a through hole, or to start threads in a blind hole, closed at the bottom.
Tap Drills are smaller in diameter than the screw shaft to leave enough metal to cut threads.
Clearance Drills are large enough to allow the body of the bolt to pass through the hole.
Tap Drill: for 6-.75mm, use metric Drill- 5.25mm