drill bit size.pdf

Metric drill set, 1.0-6.0

mm by 0.1 mm, jobber

length

Drill bit sizesFrom Wikipedia, the free encyclopedia

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.

A comprehensive table for metric, fractional wire and tapping sizes can be found at the drill and tap

size chart.

Contents

1 Metric drill bit sizes■

2 Fractional-inch drill bit sizes ■

2.1 Decimal-fraction equivalents: 0 to 1 by 64ths■

3 US number and letter gauge drill bit sizes ■

4 Drill Bit Conversion Table■

5 Screw-machine-length drill■

6 Jobber-length drill■

7 Long series drill bits■

8 Center drill bit sizes■

9 See also■

Metric drill bit sizes

Metric drill bit sizes define the diameter of the bit in terms of standard

metric lengths. Standards organizations define sets of sizes that are

conventionally manufactured and stocked. For example, British Standard

BS 328 defines sizes from 0.2 mm to 25.0 mm.

From 0.2 through 0.98 mm, sizes are defined as follows, where N is an

integer from 2 through 9:

N · 0.1 mm■

N · 0.1 + 0.02 mm■

N · 0.1 + 0.05 mm■

N · 0.1 + 0.08 mm■

From 1.0 through 2.95 mm, sizes are defined as follows, where N is an

integer from 10 through 29:

N · 0.1 mm■

N · 0.1 + 0.05 mm■

of 7Drill bit sizes - Wikipedia, the free encyclopedia

5/22/2013http://en.wikipedia.org/wiki/Drill_bit_sizes

Fractional drill bit set by

Craftsman

From 3.0 through 13.9 mm, sizes are defined as follows, where N is an integer from 30 through 139:

N · 0.1 mm■

From 14.0 through 25.0 mm, sizes are defined as follows, where M is an integer from 14 through 25:

M · 1 mm■

M · 1 + 0.25 mm■

M · 1 + 0.5 mm■

M · 1 + 0.75 mm■

In smaller sizes, bits are available in smaller diameter increments. This reflects both the smaller drilled

hole diameter tolerance possible on smaller holes, and also the wishes of designers to have drill bit sizes

available within at most 10% of an arbitrary size hole.

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. In 0.5 mm increments, any hardware store. In 0.1 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 BS328 apply only

to twist drill bits. For example, a set of forstner bits may contain 10, 15, 20, 25 and 30 mm diameter

cutters.

Fractional-inch drill bit sizes

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 1/64 inch increments

up to 1¾ inch, then 1/32 inch increments up to 2¼ inch, 1/16 inch

increments up to 3 inches, 1/8 inch increments up to 3¼ inches, and a single

1/4 inch increment to 3½ inches.

One disadvantage of this scheme of sizing is that the size increment

between drill bits is very large for the smaller sizes, 100% for the first step.

The implication is that number gauge drill bits have to be used to bridge the

gaps.

Another disadvantage is the convention in labelling the bits. Rather than an

integral number of 64ths of an inch, drill bit sizes are written down as

irreducible fractions. So, instead of 78/64 inch, or 1 14/64 inch, the size is

always written as 1 7/32 inch. This can lead to confusion and mistakes

unless great care is taken.



Click this thumbnail to see the chart

as a landscape-oriented image.

A #80 drill bit.

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). (Decimal places for .25, .5, and .75 are shown to thousandths [.250,

.500, .750], which is how machinists usually think about them ["two-fifty", "five hundred", "seven-

fifty"]. Machinists generally truncate the decimals after thousandths; for example, a 27/64" 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 now have been largely discarded in favour of metric sizes.

Decimal-fraction equivalents: 0 to 1 by 64ths

0.000

1 .015625 64

1 .03125 32

3 .046875 64

See the rest of the chart →.

US number and letter gauge drill bit sizes

Number drill bit gauge sizes are analogous to, but different from, American

wire gauge. (See the conversion table below).

Number gauge is routinely used from size 80 (the smallest) to size 1 (the

largest) followed by letter gauge size A (the smallest) to size Z (the largest).

Number gauge is actually defined at least down to size 97, but these smaller

sizes are rarely encountered. It happens that as the technology for making

small drill bits and drilling small holes has become more available, metric

measurements have become the norm.

Number and letter gauge drill bits are almost always twist drill bits. There is no particular reason why

the gauge cannot be used to measure bits of other types, but the gauge covers a size range across which

the twist drill bit is the most commonly used.

The gauge-to-diameter conversion does not follow a set formula, but rather was defined as a useful and

practical measure. The graph shows how gauge diameters change with gauge. Each step along the

horizontal axis is one gauge size. The step size between adjacent gauges is smaller for smaller gauges.

This is appropriate, because the tolerance of the diameter of drilled holes is closer for smaller drill bits.

The increment from one gauge to the next for a number 92 drill bit at 0.2 mm diameter is just 5%,

compared to 10% for standard metric sizes. Number and letter gauge drill bits are still in common use in

the U.S. In the past, they were popular elsewhere, but now have been largely discarded in favor of

metric sizes.



click to see a ruler comparing

millimetres to fractions of an inch

The US number and letter size drills are sized as needed to provide proper clearance holes for screws

and bolts according to ASME B18.2.8. There are three fit classes for clearance holes: close, normal, and

loose. Some of the clearances required are not in increments of 1/64 or 1/32. This necessitates ranges of

drill sizes in between the fractional sizes, especially in the smaller diameter numbered screw sizes.

Drill Bit Conversion Table

See also: drill and tap size chart



gauge in/mm

80 0.0135 in/0.343 mm

79 0.0145 in/0.368 mm

78 0.016 in/0.406 mm

77 0.018 in/0.457 mm

76 0.020 in/0.508 mm

75 0.021 in/0.533 mm

74 0.0225 in/0.572 mm

73 0.024 in/0.610 mm

72 0.025 in/0.635 mm

71 0.026 in/0.660 mm

70 0.028 in/0.711 mm

69 0.0292 in/0.742 mm

68 0.031 in/0.787 mm

67 0.032 in/0.813 mm

66 0.033 in/0.838 mm

65 0.035 in/0.889 mm

64 0.036 in/0.914 mm

63 0.037 in/0.940 mm

62 0.038 in/0.965 mm

61 0.039 in/0.991 mm

60 0.040 in/1.016 mm

59 0.041 in/1.041 mm

58 0.042 in/1.067 mm

57 0.043 in/1.092 mm

56 0.0465 in/1.181 mm

55 0.052 in/1.321 mm

54 0.055 in/1.397 mm

gauge in/mm

53 0.0595 in/1.511 mm

52 0.0635 in/1.613 mm

51 0.067 in/1.702 mm

50 0.070 in/1.778 mm

49 0.073 in/1.854 mm

48 0.076 in/1.930 mm

47 0.0785 in/1.994 mm

46 0.081 in/2.057 mm

45 0.082 in/2.083 mm

44 0.086 in/2.184 mm

43 0.089 in/2.261 mm

42 0.0935 in/2.375 mm

41 0.096 in/2.438 mm

40 0.098 in/2.489 mm

39 0.0995 in/2.527 mm

38 0.1015 in/2.578 mm

37 0.104 in/2.642 mm

36 0.1065 in/2.705 mm

35 0.110 in/2.794 mm

34 0.111 in/2.819 mm

33 0.113 in/2.870 mm

32 0.116 in/2.946 mm

31 0.120 in/3.048 mm

30 0.1285 in/3.264 mm

29 0.136 in/3.454 mm

28 0.1405 in/3.569 mm

27 0.144 in/3.658 mm

gauge in/mm

26 0.147 in/3.734 mm

25 0.1495 in/3.797 mm

24 0.152 in/3.861 mm

23 0.154 in/3.912 mm

22 0.157 in/3.988 mm

21 0.159 in/4.039 mm

20 0.161 in/4.089 mm

19 0.166 in/4.216 mm

18 0.1695 in/4.305 mm

17 0.173 in/4.394 mm

16 0.177 in/4.496 mm

15 0.180 in/4.572 mm

14 0.182 in/4.623 mm

13 0.185 in/4.699 mm

12 0.189 in/4.801 mm

11 0.191 in/4.851 mm

10 0.1935 in/4.915 mm

9 0.196 in/4.978 mm

8 0.199 in/5.055 mm

7 0.201 in/5.105 mm

6 0.204 in/5.182 mm

5 0.2055 in/5.220 mm

4 0.209 in/5.309 mm

3 0.213 in/5.410 mm

2 0.221 in/5.613 mm

1 0.228 in/5.791 mm

- -

gauge

A 0.234 in/5.944 mm

B 0.238 in/6.045 mm

C 0.242 in/6.147 mm

D 0.246 in/6.248 mm

E 0.250 in/6.350 mm

F 0.257 in/6.528 mm

G 0.261 in/6.629 mm

H 0.266 in/6.756 mm

I 0.272 in/6.909 mm

J 0.277 in/7.036 mm

K 0.281 in/7.137 mm

L 0.290 in/7.366 mm

M 0.295 in/7.493 mm

N 0.302 in/7.671 mm

O 0.316 in/8.026 mm

P 0.323 in/8.204 mm

Q 0.332 in/8.433 mm

R 0.339 in/8.611 mm

S 0.348 in/8.839 mm

T 0.358 in/9.093 mm

U 0.368 in/9.347 mm

V 0.377 in/9.576 mm

W 0.386 in/9.804 mm

X 0.397 in/10.08 mm

Y 0.404 in/10.26 mm

Z 0.413 in/10.49 mm

- -

Screw-machine-length drill

The shortest standard-length drills (that is, lowest length-to-diameter ratio) are screw-machine-length

drills. They get their name from their most common application: use in screw machines. Given the

industrial nature of most demand for screw-machine-length drills, they are generally sold only by

metalworking supply businesses (not in hardware stores or home centers).



11/32 inch drills - long-series morse, plain

morse, jobber

Center drills, Numbers 1 (bottom)

through to 6 (top)

Jobber-length drill

Jobber-length drills are the most common type of drill. The length of the flutes is between nine and

fourteen times the diameter of the drill, depending on the Drill size. So a 1⁄2 in (12.7 mm) diameter drill

will be able to drill a hole 4-1/2" deep since it is nine times the diameter in length. A 1/8 Dia Drill can

drill a hole 1-5/8" Deep since it is made thirteen times the diameter in flute length[citation needed]

Long series drill bits

The image shows a long series drill compared to its

diametric equivalents, all are 11⁄32 inches (8.7 mm) in

diameter. The equivalent morse taper drill shown in the

middle is of the usual length for a taper shank drill. The

lower drill bit is the jobber or parallel shank equivalent.

Center drill bit sizes

Center drills are available with two different included angles; 60

degrees is the standard for drilling centre holes (for example for

subsequent centre support in the lathe), but 90 degrees is also

common and used when locating holes prior to drilling with twist

drills.



Size DesignationDrill Diameter [inches (mm)]

5/0 0.010 in (0.254 mm)

4/0 0.015 in (0.381 mm)

3/0 0.020 in (0.508 mm)

2/0 0.025 in (0.635 mm)

0 1⁄32 in (0.794 mm)

1 3⁄64 in (1.191 mm)

2 5⁄64 in (1.984 mm)

3 7⁄64 in (2.778 mm)

4 1⁄8 in (3.175 mm)

4½ 9⁄64 in (3.572 mm)

5 3⁄16 in (4.763 mm)

6 7⁄32 in (5.556 mm)

7 1⁄4 in (6.350 mm)

8 5⁄16 in (7.938 mm)

GaugeBody Diameter [inches (mm)]

BS1 1⁄8 in (3.175 mm)

BS2 3⁄16 in (4.763 mm)

BS3 1⁄4 in (6.350 mm)

BS4 5⁄16 in (7.938 mm)

BS5 7⁄16 in (11.113 mm)

BS5A 1⁄2 in (12.700 mm)

BS6 5⁄8 in (15.875 mm)

BS7 3⁄4 in (19.050 mm)

See also

Drill and tap size chart■

Retrieved from "http://en.wikipedia.org/w/index.php?title=Drill_bit_sizes&oldid=549922962"

Categories: Woodworking Hole making

This page was last modified on 11 April 2013 at 23:19. ■

Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.

■



drill bit size.pdf

Documents