The tap size chart provides a list of standard size taps, each of which specifies a measurement of the diameter and thread spacing. The major diameter (outer diameter) of a tap may be listed in the fractional, metric, or screw size measurement system. The fractional system specifies the diameter in inches, while the metric system lists the diameter in millimeters following the letter "M". A screw size number corresponds to a major diameter, which is larger for a higher screw size. The decimal equivalent of the major diameter for every tap size is provided in both English (inches) and Metric (millimeters) units. The thread spacing, which may be coarse or fine, is listed after the diameter. In the fractional and screw size systems, the thread count, measured in threads per inch, is listed. The metric system provides the thread pitch in millimeters, which is the distance between threads. For each thread count, the equivalent thread pitch is provided and for metric taps, the approximate thread count is listed based on the pitch. Lastly, the recommended tap drill size is provided for each standard tap size. This size drill bit should be used for drilling the initial hole that will then be tapped.
Download charts: English Metric