Metric drill bit sizes
– Metric drill bit sizes are defined in terms of standard metric lengths.
– British Standard BS 328 defines 230 sizes from 0.2mm to 25.0mm.
– Sizes from 0.2mm to 0.98mm are defined in increments of 0.1mm.
– Sizes from 1.0mm to 2.95mm are defined in increments of 0.1mm and 0.05mm.
– Sizes from 3.0mm to 13.9mm are defined in increments of 0.1mm.
Fractional-inch drill bit sizes
– Fractional-inch drill bit sizes are commonly used in the United States.
– 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.
– For Morse taper-shank drill bits, the standard continues in larger increments.
– Drill bit sizes are written as irreducible fractions, such as 17/32 inch.
– Decimal-fraction equivalents are often used for fractional-inch drill bit sizes.
Decimal-fraction equivalents
– Decimal-fraction equivalents are used for fractional-inch drill bit sizes.
– The equivalents range from 1/64 inch to 1 inch by 64ths.
– Machinists usually think about decimal places to thousandths.
– The chart provides the decimal-fraction equivalents for each 64th increment.
– The equivalents are often truncated after thousandths.
Number and letter gauge drill bit sizes
– Number drill bit gauge sizes range from size 80 (the smallest) to size 1 (the largest).
– Letter gauge sizes range from size A (the smallest) to size Z (the largest).
– The gauge-to-diameter ratio is based on the Stubs Steel Wire Gauge.
– Number and letter gauge drill bits are commonly used for twist drill bits.
– These sizes are still in common use in the U.S. and to a lesser extent in the UK.
Drill bit conversion table
– The drill bit conversion table provides a comparison between millimeters and fractions of an inch.
– The table includes gauge sizes and their corresponding decimal and fractional equivalents.
– The table helps in converting between different measurement systems.
– It is useful for selecting the appropriate drill bit size for a specific task.
– The table is often used in conjunction with a drill and tap size chart. Source: https://en.wikipedia.org/wiki/Drill_bit_sizes
Drill bits are the cutting tools of drilling machines. They can be made in any size to order, but standards organizations have defined sets of sizes that are produced routinely by drill bit manufacturers and stocked by distributors.
In the U.S., fractional inch and gauge drill bit sizes are in common use. In nearly all other countries, metric drill bit sizes are most common, and all others are anachronisms or are reserved for dealing with designs from the US. The British Standards on replacing gauge size drill bits with metric sizes in the UK was first published in 1959.[citation needed]
A comprehensive table for metric, fractional wire and tapping sizes can be found at the drill and tap size chart.
