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Drill bit sizes are written as irreducible fractions. So, instead of 78/64 inch, or 1 14/64 inch, the size is noted as 1 7/32 inch. Below is a chart providing the decimal-fraction equivalents that are most relevant to fractional-inch drill bit sizes (that is, 0 to 1 by 64ths).
Such an appropriately sized drill is called a tap drill for that size of thread, because it is a correct drill to be followed by the tap. Many thread sizes have several possible tap drills, because they yield threads of varying thread depth between 50% and 100%.
English: a ruler from 0 to 1 inch (in.) in 1/32 inch divisions below the line and 1/2 millimetre (mm) divisions above the line to give a visual representation of the approximations. Principally designed to help visually determine if a metric or imperial drill bit will suffice.
The metric screw tap and clearance sizes are largely missing, and those clearance hole sizes that are present are more often incorrect; e.g. M5 x 0.8 has 5.1 mm as close fit, but this would be an interference fit, all sources have 5.3 mm. (0.1 mm is below the sum of surface roughness and tolerance of the screw and clearance drill diameter ...
Nowadays, the drill bit is usually made by rotating the bar while moving it past a grinding wheel to cut the flutes in the same manner as cutting helical gears. Twist drill bits range in diameter from 0.002 to 3.5 in (0.051 to 88.900 mm) [9] and can be as long as 25.5 in (650 mm). [10]
So a 1⁄2 in (12.7 mm) diameter drill will be able to drill a hole 4 1⁄2 in (114.3 mm) deep since it is nine times the diameter in length. A 1⁄8 in (3.2 mm) diameter drill can drill a hole 1 5⁄8 in (41.3 mm) deep since it is thirteen times the diameter in flute length[citation needed]
where is the tap drill size, is the major diameter of the tap (e.g., 10 mm for a M10×1.5 tap), and pitch is the pitch of the thread (1.5 mm in the case of a standard M10 tap) and so the correct drill size is 8.5 mm. This works for both fine and coarse pitches, and also produces an approximate 75% thread.
Drill rod diameters range from 0.0135 to 1.5 in (0.34 to 38.10 mm); in the United States diameters smaller than 27 ⁄ 64 th of an inch (11 mm) are made in letter drill sizes and number drill sizes, in addition to fractional sizes. Lengths are usually one or three feet (0.3048 or 0.9144 m).