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Gaugeįractional drill bits are definedby the ANSI B94.11M-1979 standard. The drill size chart below contains imperial and metric drill bit diameter measurements for all number and letter gauges.
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Most other countries, especially in Europe, have abandoned them entirely in favour of metric systems. They are also seen in the UK to a lesser degree, having been largely replaced by metric sizes. They are loosely based on the Stubs Steel Wire Gauge, with gauge sizes that are similar (but not entirely identical) to that system.Īlthough they originated in the 19 thcentury, these gauges are still commonly used in the U.S. Number and letter gauges do not follow a formula or standard increments.
Metric drill bits series#
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To measure the diameter of a drill bit, it’s best to measure the cutting edge rather than the shank (the shank is the part that is held by the drill chuck).