Metric dimensioning is routinely used for drill bits of all types, although the details of BS 328 apply only to twist drill bits. color: 333399; The gauge-to-diameter ratio is not defined by a formula; it is based on—but is not identical to—the Stubs Steel Wire Gauge, which originated in Britain during the 19th century. Engineering Slide Chart ANSI Drill Sizes & Hardware Selector, Machinist Drill Bit Size Table | Drill Bit Size Chart | ISO Metric Drill Bit Size Table, For typical mechanical tolerances that are achievable see: Drilling Tolerances Capabilities Chart, Fractional and Metric Sizes per. Other countries that formerly used the number series have for the most part also abandoned these in favour of metric sizes. 3.30 mm.