Before Helicoil insert installation , the drilled hole has to be tapped with a Helicoil STI hand tap or machine tap of the correct tap size. Types of Helicoil Taps available include: Helicoil Taper Tap (Helicoil Roughing Tap) - 4 thread chamfer - used for difficult tapping operations and for starting tapping operations on difficult holes Helicoil Intermediate Tap (Helicoil Finishing Tap) - 4 thread chamfer - used for hand or machine tapping in through holes and blind holes where ample chip clearance is available Helicoil Plug Tap (Helicoil Bottoming Tap) - 2 thread chamfer - used for tapping blind holes where a maximum number of fully-formed threads are needed in minimum depth holes Helicoil Spiral Flute Tap (Machine Tap) - 2 thread chamfer - can be used manually or attached to tapping drivers Helicoil Spiral Point Tap (Machine Tap) 2 thread chamfer - similar to spiral flute taps except that they are more suitable for through holes on less abrasive materials