It is usually necessary to look at a tap drill or tap size chart to find the appropriate drill bit size for a tap, many of which can be found online. Some tap drill charts provide the appropriate tap to drill bit conversion in both imperial and metric measurements.
Taps are generally used in parts manufacturing, as it is often necessary to create a hole with female screw threads that can accept a male screw when fastening and building a finished assembly. Although there are several ways to create this type of female screw hole, drilling a hole with the appropriate size drill bit and then using a tap to thread the hole is one of the more common.
Every standard size tap has one or more drill bit sizes that correspond to it, which are slightly larger than the skinniest part of the male screw but slightly smaller than the thickest part of the screw. In order to find the appropriate tap and drill bit size, it is necessary to know whether the screws being used are coarse or fine. Known as thread spacing, this is important in determining the correct drill bit size. This is because the tap can create varying thread depths between 50 and 100 percent, depending on how large the hole is.