Drilling is a process of producing a hole while tapping is a technique used to cut a thread inside a hole, so the drill bit and tapping tool are often used in sequential to fabricate CNC parts with thread holes. When it comes to the selection of drill bit sizes and tap sizes, there are standard drill and tap size chart for reference.
When manufacturing custom CNC machining parts, holes with screw threads are often required for fastening the finished part or facilitating the building. One of the most common ways to produce the thread holes is to drill a hole of the right size with a drill bit and tap it with a tap. People would need a drill size chart and tap size chart to determine the proper tap drill for a certain thread size or proper tap for an existing hole.
The drill size chart is a table list standard size drill bits in several measurement systems, including fractional, metric, wire gauge number, and letter. Fractional sizes are measured in inches, while metric sizes are measured in millimeters. The wire gauge and letter systems refer to tool diameters that increase as the wire gauge decreases from #107 to #1 and then continues from A to Z. The decimal equivalents of the diameters are shown in both English and Metric units.
The tap size chart is a table that lists standard size taps, specifying the diameter and thread spacing, for fractional, metric, and screw sizes. Fractional sizes are listed in inches, 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 can be coarse or fine, will be listed after the diameter. In the fractional and screw size systems, the thread count is used, measured in threads per inch, such as UNF threads and UNC threads. The metric system uses the thread pitch, which is the distance between threads, measured in millimeters.
Metric drill bit sizes: diameter of the bit in terms of standard metric lengths.
Letter drill bit sizes: the sizes are indicated in letters, from size A (the smallest) to size Z (the largest).
Number drill bit sizes: the sizes are indicated in numbers, range from size 80 (the smallest) to size 1 (the largest). Number and letter sizes are commonly used for twist drill bits rather than other drill forms.
Fractional drill bit sizes: the sizes are written as irreducible fractions. ANSI B94.11M-1979 sets size standards for jobber-length straight-shank twist drill bits from 1/64 inch through 1 inch in 1/64 inch increments.
Decimal drill bit sizes: written in number with 4 decimal places, equivalent to fractional-inch drill bit sizes
Drill Bit Sizes (Metric)
The drill size chart contains tools up to 1.5 inches in diameter, but larger tools are also commonly used.
Drill Bit Sizes (English)
Tap Sizes (Metric)
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.
Tap Sizes (English)