121.5 Metric Tap Standard Equivalent

The table below shows the metric and English tap standards and their decimal equivalents. You can use this information to determine the correct size for your project. The chart lists the diameter, thread spacing, and thread count of different types of taps. The sizes are listed after the letter “M.” Fractional sizes are listed first in inches and a corresponding metric size follows with the letter “M”. The screw size number is listed after the diameter. In the English system, the thread pitch is used to measure the distance between threads.