Our tap drill chart is designed to help you find the correct tap size based on the fasteners you’re using. Use our drill and tap chart to find the proper tap size in UNC, UNF, metric, and more.
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Tap Drill Chart FAQs
To read a tap drill chart, look at the bolt specifications to find the size, threads per inch, and standard. Select a chart, find the correct size in the first column, then find the correct threads per inch in the next column. The columns to the right of these numbers are the preferred tapping drill size for that fastener.
Using a tap drill chart is the easiest way to figure out the correct drill size for a tap. For metric sizes, you can subtract the thread pitch from the major diameter (Diameter - Pitch) to calculate the correct size.
Common drill tap chart mistakes include using the wrong chart, misinterpreting numbers, and aiming for full thread engagement. It’s also important to consider the materials you’re using.
Pilot holes are small holes designed to prevent materials from splitting when installing screws, while tap holes are specifically sized holes that are designed to provide optimal thread engagement.
Imperial thread sizes are used primarily in North America and are represented in inches, while metric sizes are used in most parts of the world and are represented in millimeters.
UNC, UNF, and NPT are American thread standards. UNC (Unified National Coarse) is for general use, UNF (Unified National Fine) is for precision use in automotive and aerospace, and NPT (National Pipe Thread) is for plumbing, gas lines, and hydraulics.