Hiw to Read the Center Point Libes on a Twist Drill Bit Gauge

Drill bits are the cutting tools of drilling machines. They tin be made in any size to order, but standards organizations have divers sets of sizes that are produced routinely by drill bit manufacturers and stocked by distributors.

In the U.South., partial inch and gauge drill fleck sizes are in mutual utilize. In virtually all other countries, metric drill fleck sizes are virtually mutual, and all others are anachronisms or are reserved for dealing with designs from the US. The British Standards on replacing gauge size drill $.25 with metric sizes in the U.k. was first published in 1959.^{[ citation needed ]}

A comprehensive tabular array for metric, fractional wire and tapping sizes can be establish at the drill and tap size chart.

Metric drill bit sizes [edit]

Metric drill set, 1.0–6.0 mm by 0.1 mm, jobber length. The case that holds them in an indexed order (by size), via a graduated series of holes, is called a drill index.

Metric drill fleck sizes define the diameter of the chip in terms of standard metric lengths. Standards organizations ascertain sets of sizes that are conventionally manufactured and stocked. For example, British Standard BS 328 defines 230 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:

• North · 0.1 mm
• North · 0.1 + 0.02 mm
• N · 0.ane + 0.05 mm
• Due north · 0.1 + 0.08 mm

From 1.0 through ii.95 mm, sizes are divers as follows, where N is an integer from 10 through 29:

• North · 0.1 mm
• N · 0.1 + 0.05 mm

From 3.0 through thirteen.9 mm, sizes are defined as follows, where North is an integer from 30 through 139:

• N · 0.one mm

From xiv.0 through 25.0 mm, sizes are defined every bit follows, where Yard is an integer from 14 through 25:

• M · one mm
• M · ane + 0.25 mm
• M · i + 0.5 mm
• M · i + 0.75 mm

In smaller sizes, bits are available in smaller diameter increments. This reflects both the smaller drilled hole bore tolerance possible on smaller holes and the wishes of designers to take drill fleck sizes available within at most 10% of an arbitrary pigsty size.

The cost and availability of detail size bits does non change uniformly across the size range. Bits at size increments of one mm are near commonly available, and lowest cost. Sets of bits in 1 mm increments might be found on a market stall. In 0.v mm increments, any hardware store. In 0.1 mm increments, any engineers' store. Sets are not commonly bachelor in smaller size increments, except for drill bits below 1 mm diameter. Drill $.25 of the less routinely used sizes, such as ii.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 $.25, where information technology is rare to detect a assail the market which does not contain every gauge.

In that location are besides Renard series sequences of preferred metric drill bits:^[1]

• R5 (gene i.58) : M2.5, M4, M6, M10, M16, M24
• R10 (factor 1.26): M3, M5, M8, M12, M20, M30

Metric dimensioning is routinely used for drill $.25 of all types, although the details of BS 328 apply just 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 [edit]

Fractional-inch drill chip sizes are still in common utilise in the The states and in whatever factory (around the earth) that makes inch-sized products for the U.S. market.

ANSI B94.11M-1979 sets size standards for jobber-length straight-shank twist drill bits from 1/64 inch through i inch in i/64 inch increments. For Morse taper-shank drill $.25, the standard continues in 1/64 inch increments up to 1¾ inch, then ane/32 inch increments up to two¼ inch, 1/16 inch increments upwardly to iii inches, 1/eight inch increments upward to three¼ inches, and a single 1/4 inch increment to 3½ inches. 1 aspect of this method of sizing is that the size increment between drill bits becomes larger as bit sizes get smaller: 100% for the step from 1/64 to one/32, but a much smaller pct between ane 47/64 and ane iii/four.

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 seven/32 inch.

Beneath is a chart providing the decimal-fraction equivalents that are most relevant to fractional-inch drill bit sizes (that is, 0 to ane past 64ths). (Decimal places for .25, .five, and .75 are shown to thousandths [.250, .500, .750], which is how machinists ordinarily think most them ["two-50", "five hundred", "vii-fifty"]. Machinists more often than not truncate the decimals afterwards thousandths; for example, a 27/64" drill bit may be referred to in store-floor spoken language every bit a "four-20-ane drill".)

Charts like this, printed at affiche size, are widely posted on motorcar shop walls for handy reference past machinists as they work. For some tasks it is faster and less annoying to glance downwards a column of numbers on a poster than it is to punch calculator buttons or do penciled arithmetic.

For anyone looking to create such a poster or to tailor the design and colors to their own preferences, spreadsheet software makes this fast and easy to practise. The tools that the software provides—formulas, cell formatting with rounding, autofill, and sorting by numerical society—obviate whatever manual calculation and information entry. For example, i can create the inch nominal rows for the chart—with columns for inch fraction, inch decimal, and corresponding millimeter decimal conversion—using formulas, cell formatting with rounding, and autofill; and i can then create the metric nominal rows below that, with the inch decimal conversions existence provided by formula; and and so ane tin can sort the whole canvas by size guild, automatically interposing the inch nominal and metric nominal rows by size order. Font and color can exist chosen to make a affiche-size nautical chart that is easy to read from i or 2 meters abroad. Printing can be done on a desktop printer, with the letter of the alphabet-size sheets then being stapled together to make up the larger poster.

Decimal-fraction equivalents [edit]

fraction in mm 1⁄64 0.015625 0.396875 ane⁄32 0.03125 0.79375 three⁄64 0.046875 one.190625 ane⁄16 0.0625 1.5875 5⁄64 0.078125 1.984375 three⁄32 0.09375 2.38125 vii⁄64 0.109375 2.778125 ane⁄8 0.125 iii.175 9⁄64 0.140625 3.571875 5⁄32 0.15625 3.96875 11⁄64 0.171875 4.365625 three⁄sixteen 0.1875 iv.7625 xiii⁄64 0.203125 5.159375 seven⁄32 0.21875 5.55625 fifteen⁄64 0.234375 five.953125 1⁄4 0.250 6.350

fraction in mm 17⁄64 0.265625 half dozen.746875 nine⁄32 0.28125 7.14375 19⁄64 0.296875 vii.540625 v⁄xvi 0.3125 vii.9375 21⁄64 0.328125 eight.334375 11⁄32 0.34375 8.73125 23⁄64 0.359375 9.128125 3⁄8 0.375 nine.525 25⁄64 0.390625 9.921875 13⁄32 0.40625 10.31875 27⁄64 0.421875 x.715625 7⁄sixteen 0.4375 11.1125 29⁄64 0.453125 11.509375 15⁄32 0.46875 xi.90625 31⁄64 0.484375 12.303125 i⁄ii 0.500 12.700

fraction in mm 33⁄64 0.515625 13.096875 17⁄32 0.53125 thirteen.49375 35⁄64 0.546875 13.890625 9⁄16 0.5625 14.2875 37⁄64 0.578125 xiv.684375 19⁄32 0.59375 15.08125 39⁄64 0.609375 15.478125 5⁄8 0.625 15.875 41⁄64 0.640625 16.271875 21⁄32 0.65625 16.66875 43⁄64 0.671875 17.065625 11⁄16 0.6875 17.4625 45⁄64 0.703125 17.859375 23⁄32 0.71875 18.25625 47⁄64 0.734375 18.653125 3⁄4 0.750 19.050

fraction in mm 49⁄64 0.765625 19.446875 25⁄32 0.78125 19.84375 51⁄64 0.796875 20.240625 thirteen⁄16 0.8125 twenty.6375 53⁄64 0.828125 21.034375 27⁄32 0.84375 21.43125 55⁄64 0.859375 21.828125 7⁄viii 0.875 22.225 57⁄64 0.890625 22.621875 29⁄32 0.90625 23.01875 59⁄64 0.921875 23.415625 15⁄16 0.9375 23.8125 61⁄64 0.953125 24.209375 31⁄32 0.96875 24.60625 63⁄64 0.984375 25.003125 1 one.000 25.400

Number and letter judge drill bit sizes [edit]

Number drill bit estimate sizes range from size eighty (the smallest) to size 1 (the largest) followed by letter judge size A (the smallest) to size Z (the largest). Although the ASME B94.11M twist drill standard, for example, lists sizes as small as size 97, sizes smaller than 80 are rarely encountered in practice.

Number and alphabetic character sizes are commonly used for twist drill bits rather than other drill forms, equally the range comprehend the sizes for which twist drill bits are virtually frequently used.

The gauge-to-diameter ratio is not defined by a formula; information technology is based on—only is not identical to—the Stubs Steel Wire Approximate, which originated in U.k. during the 19th century.^[2] The accompanying graph illustrates the modify in bore with change in gauge, every bit well as the reduction in footstep size as the gauge size decreases. Each stride along the horizontal axis is one gauge size.

Number and letter gauge drill $.25 are still in common utilize in the U.S. and to a lesser extent the United kingdom of great britain and northern ireland, where they have largely been supplanted by metric sizes. Other countries that formerly used the number series have for the most role too abandoned these in favour of metric sizes.^{[ commendation needed ]}

Drill bit conversion table [edit]

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

gauge in mm 104 0.0031 0.079 103 0.0035 0.089 102 0.0039 0.099 101 0.0043 0.109 100 0.0047 0.119 99 0.0051 0.130 98 0.0055 0.140 97 0.0059 0.150 96 0.0063 0.160 95 0.0067 0.170 94 0.0071 0.180 93 0.0075 0.191 92 0.0079 0.201 91 0.0083 0.211 xc 0.0087 0.221 89 0.0091 0.231 88 0.0095 0.241 87 0.010 0.254 86 0.0105 0.267 85 0.011 0.279 84 0.0115 0.292 83 0.012 0.305 82 0.0125 0.318 81 0.013 0.330 80 0.0135 0.343 79 0.0145 0.368

estimate in mm 78 0.016 0.406 77 0.018 0.457 76 0.020 0.508 75 0.021 0.533 74 0.0225 0.572 73 0.024 0.610 72 0.025 0.635 71 0.026 0.660 seventy 0.028 0.711 69 0.0292 0.742 68 0.031 0.787 67 0.032 0.813 66 0.033 0.838 65 0.035 0.889 64 0.036 0.914 63 0.037 0.940 62 0.038 0.965 61 0.039 0.991 60 0.040 1.016 59 0.041 one.041 58 0.042 1.067 57 0.043 1.092 56 0.0465 one.181 55 0.052 ane.321 54 0.055 ane.397 53 0.0595 1.511

approximate in mm 52 0.0635 one.613 51 0.067 i.702 50 0.070 1.778 49 0.073 1.854 48 0.076 one.930 47 0.0785 1.994 46 0.081 two.057 45 0.082 2.083 44 0.086 2.184 43 0.089 2.261 42 0.0935 2.375 41 0.096 2.438 forty 0.098 2.489 39 0.0995 2.527 38 0.1015 2.578 37 0.104 2.642 36 0.1065 2.705 35 0.110 2.794 34 0.111 2.819 33 0.113 2.870 32 0.116 two.946 31 0.120 3.048 30 0.1285 3.264 29 0.136 iii.454 28 0.1405 3.569 27 0.144 iii.658

gauge in mm 26 0.147 three.734 25 0.1495 three.797 24 0.152 three.861 23 0.154 3.912 22 0.157 3.988 21 0.159 4.039 twenty 0.161 4.089 19 0.166 4.216 18 0.1695 four.305 17 0.173 4.394 16 0.177 4.496 15 0.180 4.572 fourteen 0.182 iv.623 13 0.185 4.699 12 0.189 iv.801 eleven 0.191 4.851 10 0.1935 4.915 9 0.196 4.978 8 0.199 five.055 7 0.201 v.105 six 0.204 five.182 five 0.2055 5.220 4 0.209 five.309 3 0.213 five.410 2 0.221 5.613 one 0.228 v.791

approximate in mm A 0.234 5.944 B 0.238 vi.045 C 0.242 six.147 D 0.246 6.248 E 0.250 half-dozen.350 F 0.257 half dozen.528 Thousand 0.261 vi.629 H 0.266 6.756 I 0.272 6.909 J 0.277 vii.036 Thou 0.281 7.137 50 0.290 vii.366 M 0.295 7.493 N 0.302 seven.671 O 0.316 8.026 P 0.323 viii.204 Q 0.332 8.433 R 0.339 8.611 S 0.348 eight.839 T 0.358 9.093 U 0.368 nine.347 V 0.377 9.576 Westward 0.386 9.804 X 0.397 x.08 Y 0.404 10.26 Z 0.413 x.49

Screw-machine-length drill [edit]

The shortest standard-length drills (that is, lowest length-to-diameter ratio) are screw-motorcar-length drills (sometimes abbreviated Southward/M). They are named for their use in spiral machines. Their shorter flute length and shorter overall length compared to a standard jobber chip results in a more rigid drill bit, reducing deflection and breakage. They are rarely available in retail hardware stores or home centers.

Jobber-length drill [edit]

Jobber-length drills are the most normally found type of drill. The length of the flutes is between ix and 14 times the diameter of the drill, depending on the drill size. So a one / ii  in (12.7 mm) diameter drill will be able to drill a hole 4+ 1 / 2  in (114.iii mm) deep, since it is 9 times the diameter in length. A 1 / eight  in (3.175 mm) diameter drill can drill a hole 1+ 5 / viii  in (41.275 mm) deep, since it is 13 times the bore in flute length.^[iii]

The term jobber refers to a wholesale distributor—a person or company that buys from manufacturers and sells to retailers.^{[ citation needed ]} Manufacturers producing drill bits "for the trade" (as opposed to for specialized machining applications with item length and design requirements) made ones of medium length suitable for a broad variety of jobs, considering that was the type nearly desirable for general distribution. Thus, at the time that the name of jobber-length drill bits became common, it reflected the aforementioned concept that names like general-purpose and multipurpose reflect.^{[ citation needed ]}

Aircraft-length drill [edit]

Extended-reach or long-series drills are commonly called shipping-length from their original use in manufacturing riveted aluminum aircraft. For bits thicker than a minimum size such as 1⁄eight -inch (3.175 mm), they are available in stock-still lengths such as 6, eight, 12 or 18 inches (152, 203, 305 or 457 mm) rather than the progressive lengths of jobber drills.

11/32 inch drills: long-series Morse, evidently Morse, jobber

The image shows a long-series drill compared to its diametric equivalents, all are 11⁄32 inch (8.7313 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 [edit]

Center drills, numbers 1 (lesser) through to 6 (top)

Center drills are available with two different included angles; 60 degrees is the standard for drilling centre holes (for example for subsequent heart back up in the lathe), merely xc degrees is also common and used when locating holes prior to drilling with twist drills. Center drills are made specifically for drilling lathe centers, but are often used as spotting drills considering of their radial stiffness.

Size designation Drill 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 iii⁄64  in (1.191 mm) 2 v⁄64  in (i.984 mm) 3 seven⁄64  in (ii.778 mm) 4 one⁄8  in (three.175 mm) iv½ ix⁄64  in (3.572 mm) 5 3⁄sixteen  in (iv.763 mm) six vii⁄32  in (5.556 mm) 7 one⁄four  in (6.350 mm) 8 5⁄16  in (7.938 mm)

Judge Body bore [inches (mm)] BS1 i⁄8  in (3.175 mm) BS2 3⁄sixteen  in (4.763 mm) BS3 ane⁄4  in (six.350 mm) BS4 5⁄16  in (7.938 mm) BS5 7⁄16  in (11.113 mm) BS5A ane⁄2  in (12.700 mm) BS6 5⁄eight  in (15.875 mm) BS7 3⁄four  in (nineteen.050 mm)

Spotting drill bit sizes [edit]

Spotting drills are available in a relatively small-scale range of sizes, both metric and royal, every bit their purpose is to provide a precise spot for guiding a standard twist drill. Commonly bachelor sizes are 1/8", one/4", 3/8", 1/2", 5/viii", 3/4", 4 mm, half dozen mm, eight mm, 10 mm, 12 mm, 14 mm, xvi mm and xviii mm. The drills are most commonly bachelor with either 90° or 120° included bending points.

See also [edit]

• Drill and tap size chart

References [edit]

1. ^ Dasarathi-Cadem (2 February 2017). "Preferred sizes in engineering science". CNC etc . Retrieved 6 September 2017.
2. ^ Pöll, J. S. (June 1999). "The story of the judge". Anaesthesia. 54 (vi): 575–581. doi:ten.1046/j.1365-2044.1999.00895.x. ISSN 0003-2409. PMID 10403873. S2CID 41519791.
3. ^ "Jobber Length Twist Drill Sizes".

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Source: https://en.wikipedia.org/wiki/Drill_bit_sizes

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