What type of tap is used to start threads in a hole or to tap through a hole?

• A. A taper tap
• B. A bottoming tap
• C. A plug tap
• D. A forming tap

Answer: (A)

A taper tap is designed with the longest gradual lead at the tip, so it cuts more gently as it starts the thread and guides itself through the hole. That gentle entry helps you begin a new thread cleanly and prevents the tap from binding as it advances, which is exactly what you want when starting threads or passing the tap through a hole. Once the thread is started, you’d typically finish it with a plug or bottoming tap depending on hole type, but for the initial start and for getting the tap through a hole, the taper tap is the best choice. The other taps serve different purposes—bottoming taps reach to the bottom of blind holes, plug taps finish through holes, and forming taps create threads without cutting—so they aren’t as suitable for the starting or through-hole entry role.