Special Internal Threading Tools

• Taps create female threads for male-threaded objects like bolts. Hemera Technologies/PhotoObjects.net/Getty Images

  Tools used to cut internal, or female, threads are called taps. They are cylindrical, made of steel and have threads at one end. You can insert them into previously drilled holes, and turn them clockwise to create the thread on the inside walls of the hole. As holes need to be created in different diameters, taps come in various diameters to accommodate different sizes. The three most common types of taps are tapered, plug and bottoming taps.

Tapered Tap

• A tapered tap's thread is chamfered at the end. This makes it easier to insert the tap into the previously drilled holed. It is important to insert the tap squarely -- at 90 degrees -- into the hole to create a good thread. Failure to do so creates a bad thread and can possibly break the tap while inserted in the hole.

Plug Tap

• Plug taps are the most widely used types of tap. The ends of the thread are slightly chamfered for easier access into the hole, but not as much as the tapered tap. Because the threads are less chamfered, threads can be cut closer to the end of the drilled hole.

Bottoming Tap

• The bottoming tap is chamfered even less than the tapered or plug tap. Though harder to insert correctly into the hole, the threads on the side of the tap can cut almost to the very end of the drilled hole.

Reamer

• The reamer is made of metal, is cone-shaped and tapers to a point. Spiralling blades are evenly spaced on the sides of the tapered point. Though reamers can be used to remove burrs from cut pipe ends, they are also placed into the opening of the previously drilled hole and turned slightly to countersink the hole. This allows for easier access of the tap into the hole.