Processes - Machining

The tap size chart provides a list of standard size taps, specifying the diameter and thread spacing, for fractional, metric, and screw sizes. The decimal equivalents of the diameters are shown in both English and Metric units. Fractional sizes are listed in inches, while metric sizes are listed in millimeters following the letter "M". A screw size number corresponds to a diameter which is larger for a higher screw size. The thread spacing, which may be coarse or fine, is listed after the diameter. In the fractional and screw size systems, the thread count is used, measured in threads per inch. The metric system uses the thread pitch, which is the distance between threads, measured in millimeters. For each thread count, the equivalent thread pitch is provided and for metric taps, the approximate thread count is shown 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.