Tapping is when you threads are cut into a hole. A die set is used to cut threads onto a cylinder (bolt). To use a tap or a die, first determine the number of threads per inch (TPI) of the part to be fixed. A gauge system that has a number of different pins can be used to calculate the TPI of a bolt or nut. After determining the TPI of a bolt, choose the die that corresponds to it. A tapered die will tell which side to begin using. The die fits into a special wrench that holds and guides the die.
To use the die to create new threads on a worn out bolt, place the bolt into a vise to hold it as the wrench is turned over it. Cutting metal with metal can create heat, so put some cutting oil on the bolt to lubricate it. Place the die over the bolt and hold it horizontally. Turn the wrench. The die will catch on the threads already cut into the bolt. Every couple of turns, reverse the wrench about a half a turn to clear the threads so that the die will cut better. Also, re-apply cutting oil throughout the process. Turn the wrench until the bolt comes past the top of the die.
A die set can also be used to turn an ordinary steel rod into a bolt. To do this, the rod must have a beveled end. If necessary, chamfer the end of a rod on a grinder to get a bevel. The die will not work very well with a flat-ended rod.
Lubricate the rod often, as when cutting into a worn bolt. Make turns slowly. Have a little bit of patience with this process to achieve the desired results.
To use a tap, choose the size that is appropriate for the size of the bolt or the hole you want to thread. Place the tap into the special wrench and tighten it in. Then, place the cutting end of the tap over the hole and turn. Use cutting oil to lubricate the tap. As with the die, once the tap is started, make a slight reverse turn every now and then.