Fix It and keep it

Tapping a hole is easy, but it requires the right tools.

First you should know what size screw or bolt you intent to put in the hole that you are about to tap and select the drill and tap accordingly.

You will need to know four things before you begin:

1) The size of the screw or bolt you intent to put into the hole you are about to tap.

2) The amount of threads per inch on the screw or bolt you intent to use in the newly threaded hole.

3) Tap drill size

4) Tap size.


Once you have the screw or bolt you intend to use you will need to plug the size and thread count into the following formula to determine the tap drill size you will need to use.

TD = MD - (1/N) where TD is the tap drill size, MD is the major diameter of the tap (e.g., 3/8 inch for a 3/8"-16 tap), and N is the number of threads per inch (16 in the case of a 3/8"-16 tap). For a 3/8"-16 tap, the above formula would produce 5/16 as a result, which is the correct tap drill diameter for a 3/8"-16 tap. The result produces a tap drill size that leaves enough material in the wall of the hole to result in an approximate 75 percent thread that will provide a strong anchor point for you to secure your fastener to.

The type of tap that you use is as important in determining as the correct size. There are different materials that you can tap a threaded hole into and each one will require a different type of tap. Also, the type of hole you are threading determines a specific tap as well.

Hole Types:

A Through Hole-A hole to be tapped that goes entirely through the material is called a “through hole.” A through hole can be tapped by using a tapered tap to cut the threads. Once the tap is run in and out of the hole the threads would be ready for use.

A Blind Hole-A hole that goes into a piece of material and does not go all the way through is called a “blind hole.” When tapping a blind hole you will need to determine if what you are screwing into the hole will go all the way to the bottom or not. If you want it to go all the way to the bottom you will need to use three taps. If threads are to be cut to the bottom of a blind hole, the taper tap will be followed by an intermediate, or plug tap, and then a bottoming tap to finish the operation.
First use a tapered tap to go in as far as it can then use a plug tap to continue the threads and then finally a bottoming tap to finish the threads all the way to the bottom of the hole.

When you are using a tap you need to lubricate the tap and hole to prevent the tap from getting hot and sticking that will break the tap.

There are two types of lubricant for a tap, one is like a wax and the other is tap oil.

It is not a good idea to use the wax type of lubricant on a blind hole because the wax will hold the particles that result from tapping and may cause the tap to bind inside the hole resulting in a broken tap. It is better to use the tap oil because it will allow the tap filings to run out of the hole and not get bound up in the tap.


Taps and dies are cutting tools used to create screw threads in solid substances including, but not limited to, metal, wood, and plastic. A tap is used to cut the female portion of the mating pair (e.g. a nut). A die is used to cut the male portion of the mating pair (e.g. a bolt). The process of cutting the threads in a hole is called "tapping" the hole. The process of cutting with a die is called "threading" (or sometimes "chasing", although "chasing" as a technical term can have restricted meanings).

This entry was posted on Thursday, October 29th, 2009 at 7:58 pm and is filed under Taps and Dies. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.