In nearly all other countries, metric drill bit sizes are most common, and all others are anachronisms or are standard drill size chart pdf for dealing with designs from the US. UK was first published in 1959. Standards organizations define sets of sizes that are conventionally manufactured and stocked.
For example, British Standard BS 328 defines sizes from 0. In smaller sizes, bits are available in smaller diameter increments. The price and availability of particular size bits does not change uniformly across the size range. Bits at size increments of 1 mm are most commonly available, and lowest price.
Sets of bits in 1 mm increments might be found on a market stall. 5 mm increments, any hardware store. 1 mm increments, any engineers’ store. Sets are not commonly available in smaller size increments, except for drill bits below 1 mm diameter. Drill bits of the less routinely used sizes, such as 2. 55 mm, would have to be ordered from a specialist drill bit supplier. This subsetting of standard sizes is in contrast to general practice with number gauge drill bits, where it is rare to find a set on the market which does not contain every gauge.
Metric dimensioning is routinely used for drill bits of all types, although the details of BS 328 apply only to twist drill bits. 10, 15, 20, 25 and 30 mm diameter cutters. 75 are shown to thousandths , which is how machinists usually think about them . 64″ drill bit may be referred to in shop-floor speech as a “four-twenty-one drill”. Fractional inch drill bit sizes are still in common use in the US. In the past, they were popular elsewhere, but they have now been largely discarded in favour of metric sizes. 11M twist drill standard, for example, lists sizes as small as size 97, sizes smaller than 80 are rarely encountered in practice.
Britain during the 19th century. The accompanying graph, with each step along the horizontal axis being one gauge size, illustrate the change in diameter with change in gauge, as well as the reduction in step size as the gauge size decreases. Number and letter gauge drill bits are still in common use in the U. UK, where they have largely been superseded by metric sizes. Other countries that formerly used the number series have for the most part also abandoned these in favour of metric sizes. Jobber-length drills are the most commonly found type of drill.