Drill Bit Size.pdf

Drill bit sizes - Wikipedia, the free encyclopedia

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Drill bit sizes From Wikipedia, the free encyclopedia

Drill bits are the cutting tools t ools 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 ■

http://en.wikipedia.org/wiki/Drill_bit_sizes

Metric drill set, 1.0-6.0 mm by 0.1 mm, jobber length

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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 i nch 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.


Fractional drill bit set by Craftsman

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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", "sevenfifty"]. 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 64 1

.03125

32 3 64 See the rest of the chart

.015625 .046875

Click this thumbnail to see the chart as a landscape-oriented image.

.

→

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.

A #80 drill bit.

Number and letter gauge drill bits are almost always twist dril l 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 dril l 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.


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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

click to see a ruler comparing millimetres to fractions of an inch


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gauge

in/mm

gauge

in/mm

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gauge

in/mm

gauge

80

0.0135 in/0.343 mm

53

0.0595 in/1.511 mm

26

0.147 in/3.734 mm

A

0.

79

0.0145 in/0.368 mm

52

0.0635 in/1.613 mm

25

0.1495 in/3.797 mm

B

0.

78

0.016 in/0.406 mm

51

0.067 in/1.702 mm

24

0.152 in/3.861 mm

C

0.

77

0.018 in/0.457 mm

50

0.070 in/1.778 mm

23

0.154 in/3.912 mm

D

0.

76

0.020 in/0.508 mm

49

0.073 in/1.854 mm

22

0.157 in/3.988 mm

E

0.

75

0.021 in/0.533 mm

48

0.076 in/1.930 mm

21

0.159 in/4.039 mm

F

0.

74

0.0225 in/0.572 mm

47

0.0785 in/1.994 mm

20

0.161 in/4.089 mm

G

0.

73

0.024 in/0.610 mm

46

0.081 in/2.057 mm

19

0.166 in/4.216 mm

H

0.

72

0.025 in/0.635 mm

45

0.082 in/2.083 mm

18

0.1695 in/4.305 mm

I

0.

71

0.026 in/0.660 mm

44

0.086 in/2.184 mm

17

0.173 in/4.394 mm

J

0.

70

0.028 in/0.711 mm

43

0.089 in/2.261 mm

16

0.177 in/4.496 mm

K

0.

69

0.0292 in/0.742 mm

42

0.0935 in/2.375 mm

15

0.180 in/4.572 mm

L

0.

68

0.031 in/0.787 mm

41

0.096 in/2.438 mm

14

0.182 in/4.623 mm

M

0.

67

0.032 in/0.813 mm

40

0.098 in/2.489 mm

13

0.185 in/4.699 mm

N

0.

66

0.033 in/0.838 mm

39

0.0995 in/2.527 mm

12

0.189 in/4.801 mm

O

0.

65

0.035 in/0.889 mm

38

0.1015 in/2.578 mm

11

0.191 in/4.851 mm

P

0.

64

0.036 in/0.914 mm

37

0.104 in/2.642 mm

10

0.1935 in/4.915 mm

Q

0.

63

0.037 in/0.940 mm

36

0.1065 in/2.705 mm

9

0.196 in/4.978 mm

R

0.

62

0.038 in/0.965 mm

35

0.110 in/2.794 mm

8

0.199 in/5.055 mm

S

0.

61

0.039 in/0.991 mm

34

0.111 in/2.819 mm

7

0.201 in/5.105 mm

T

0.

60

0.040 in/1.016 mm

33

0.113 in/2.870 mm

6

0.204 in/5.182 mm

U

0.

59

0.041 in/1.041 mm

32

0.116 in/2.946 mm

5

0.2055 in/5.220 mm

V

0.

58

0.042 in/1.067 mm

31

0.120 in/3.048 mm

4

0.209 in/5.309 mm

W

0.

57

0.043 in/1.092 mm

30

0.1285 in/3.264 mm

3

0.213 in/5.410 mm

X

0.

56

0.0465 in/1.181 mm

29

0.136 in/3.454 mm

2

0.221 in/5.613 mm

Y

0.

55

0.052 in/1.321 mm

28

0.1405 in/3.569 mm

1

0.228 in/5.791 mm

Z

0.

54

0.055 in/1.397 mm

27

0.144 in/3.658 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).


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Jobber-length drill Jobber-length drills are the most common type of drill. The length of the flutes is between nine and 1 fourteen times the diameter of the drill, depending on the Drill size. So a ⁄ 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.

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

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.

Center drills, Numbers 1 (bottom) through to 6 (top)


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Size Designation

Drill Diameter [inches (mm)]

Gauge

5/0

0.010 in (0.254 mm)

BS1

1

4/0

0.015 in (0.381 mm)

BS2

3

3/0

0.020 in (0.508 mm)

BS3

1

2/0

0.025 in (0.635 mm)

BS4

5

0

1

1

3

2

5

3

7

4

1

4½

9

5

3

6

7

7

1

8

5

⁄ 32 in (0.794 mm) ⁄ 64 in (1.191 mm) ⁄ 64 in (1.984 mm) ⁄ 64 in (2.778 mm)

BS5

Body Diameter [inches (mm)]

⁄ 8 in (3.175 mm)

⁄ 16 in (4.763 mm) ⁄ 4 in (6.350 mm)

⁄ 16 in (7.938 mm)

7

⁄ 16 in (11.113 mm)

BS5A 1 ⁄ 2 in (12.700 mm) BS6

5

BS7

3

⁄ 8 in (15.875 mm) ⁄ 4 in (19.050 mm)

⁄ 8 in (3.175 mm)

⁄ 64 in (3.572 mm) ⁄ 16 in (4.763 mm) ⁄ 32 in (5.556 mm) ⁄ 4 in (6.350 mm)

⁄ 16 in (7.938 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

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Drill Bit Size.pdf

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