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Mechanical Engineering Reference

Drill Bit Size Chart

Find the closest fractional, number, letter, or metric drill bit for a target hole diameter, then compare exact decimal-inch and millimeter equivalents.

Systems
Fractional, number, letter, metric
Units
Inches and millimeters
Task
Nearest, larger, or smaller match
Basis
Nominal drill diameter

Interactive selector

Find the Closest Drill Bit Size

Enter a target diameter and choose whether the result must be nearest, at least as large, or no larger.

Included systems
Best match1/4 inFractional
Decimal inches0.2500 in
Millimeters6.350 mm
Difference0.0000 in
Percent difference0.000%
Next smaller6.3 mm0.2480 in
Exact ties2 sizes1/4 in, E
Next larger6.4 mm0.2520 in

Nominal diameter only

A drill’s listed diameter does not guarantee the finished-hole diameter. Runout, wear, point geometry, machine rigidity, feed, speed, and material can change the produced hole.

Complete reference

Fractional, Number, Letter and Metric Drill Sizes

Search or filter the complete nominal-diameter cross-reference, then select up to six rows for comparison.

Search by designation, decimal inches, millimeters, or drill system. Run the finder to populate the signed difference-from-target column and highlight the selected match.

Run the finder to highlight a matched row and calculate differences.

Scroll horizontally for additional columns and vertically for more sizes. Headers remain visible.

Nominal drill bit designations with decimal-inch and millimeter equivalents. Values are ordered by unrounded diameter.
CompareNominal diameterDifference from targetBasisCopy
0.2 mm Metric 0.0079 in 0.200 mm —Nominal
0.3 mm Metric 0.0118 in 0.300 mm —Nominal
#80 Number 0.0135 in 0.343 mm —Nominal
#79 Number 0.0145 in 0.368 mm —Nominal
1/64 in Fractional 0.0156 in 0.397 mm —Nominal
0.4 mm Metric 0.0157 in 0.400 mm —Nominal
#78 Number 0.0160 in 0.406 mm —Nominal
#77 Number 0.0180 in 0.457 mm —Nominal
0.5 mm Metric 0.0197 in 0.500 mm —Nominal
#76 Number 0.0200 in 0.508 mm —Nominal
#75 Number 0.0210 in 0.533 mm —Nominal
#74 Number 0.0225 in 0.571 mm —Nominal
0.6 mm Metric 0.0236 in 0.600 mm —Nominal
#73 Number 0.0240 in 0.610 mm —Nominal
#72 Number 0.0250 in 0.635 mm —Nominal
#71 Number 0.0260 in 0.660 mm —Nominal
0.7 mm Metric 0.0276 in 0.700 mm —Nominal
#70 Number 0.0280 in 0.711 mm —Nominal
#69 Number 0.0292 in 0.742 mm —Nominal
#68 Number 0.0310 in 0.787 mm —Nominal
1/32 in Fractional 0.0312 in 0.794 mm —Nominal
0.8 mm Metric 0.0315 in 0.800 mm —Nominal
#67 Number 0.0320 in 0.813 mm —Nominal
#66 Number 0.0330 in 0.838 mm —Nominal
#65 Number 0.0350 in 0.889 mm —Nominal
0.9 mm Metric 0.0354 in 0.900 mm —Nominal
#64 Number 0.0360 in 0.914 mm —Nominal
#63 Number 0.0370 in 0.940 mm —Nominal
#62 Number 0.0380 in 0.965 mm —Nominal
#61 Number 0.0390 in 0.991 mm —Nominal
1.0 mm Metric 0.0394 in 1.000 mm —Nominal
#60 Number 0.0400 in 1.016 mm —Nominal
#59 Number 0.0410 in 1.041 mm —Nominal
#58 Number 0.0420 in 1.067 mm —Nominal
#57 Number 0.0430 in 1.092 mm —Nominal
1.1 mm Metric 0.0433 in 1.100 mm —Nominal
#56 Number 0.0465 in 1.181 mm —Nominal
3/64 in Fractional 0.0469 in 1.191 mm —Nominal
1.2 mm Metric 0.0472 in 1.200 mm —Nominal
1.3 mm Metric 0.0512 in 1.300 mm —Nominal
#55 Number 0.0520 in 1.321 mm —Nominal
#54 Number 0.0550 in 1.397 mm —Nominal
1.4 mm Metric 0.0551 in 1.400 mm —Nominal
1.5 mm Metric 0.0591 in 1.500 mm —Nominal
#53 Number 0.0595 in 1.511 mm —Nominal
1/16 in Fractional 0.0625 in 1.587 mm —Nominal
1.6 mm Metric 0.0630 in 1.600 mm —Nominal
#52 Number 0.0635 in 1.613 mm —Nominal
1.7 mm Metric 0.0669 in 1.700 mm —Nominal
#51 Number 0.0670 in 1.702 mm —Nominal
#50 Number 0.0700 in 1.778 mm —Nominal
1.8 mm Metric 0.0709 in 1.800 mm —Nominal
#49 Number 0.0730 in 1.854 mm —Nominal
1.9 mm Metric 0.0748 in 1.900 mm —Nominal
#48 Number 0.0760 in 1.930 mm —Nominal
5/64 in Fractional 0.0781 in 1.984 mm —Nominal
#47 Number 0.0785 in 1.994 mm —Nominal
2.0 mm Metric 0.0787 in 2.000 mm —Nominal
#46 Number 0.0810 in 2.057 mm —Nominal
#45 Number 0.0820 in 2.083 mm —Nominal
2.1 mm Metric 0.0827 in 2.100 mm —Nominal
#44 Number 0.0860 in 2.184 mm —Nominal
2.2 mm Metric 0.0866 in 2.200 mm —Nominal
#43 Number 0.0890 in 2.261 mm —Nominal
2.3 mm Metric 0.0906 in 2.300 mm —Nominal
#42 Number 0.0935 in 2.375 mm —Nominal
3/32 in Fractional 0.0938 in 2.381 mm —Nominal
2.4 mm Metric 0.0945 in 2.400 mm —Nominal
#41 Number 0.0960 in 2.438 mm —Nominal
#40 Number 0.0980 in 2.489 mm —Nominal
2.5 mm Metric 0.0984 in 2.500 mm —Nominal
#39 Number 0.0995 in 2.527 mm —Nominal
#38 Number 0.1015 in 2.578 mm —Nominal
2.6 mm Metric 0.1024 in 2.600 mm —Nominal
#37 Number 0.1040 in 2.642 mm —Nominal
2.7 mm Metric 0.1063 in 2.700 mm —Nominal
#36 Number 0.1065 in 2.705 mm —Nominal
7/64 in Fractional 0.1094 in 2.778 mm —Nominal
#35 Number 0.1100 in 2.794 mm —Nominal
2.8 mm Metric 0.1102 in 2.800 mm —Nominal
#34 Number 0.1110 in 2.819 mm —Nominal
#33 Number 0.1130 in 2.870 mm —Nominal
2.9 mm Metric 0.1142 in 2.900 mm —Nominal
#32 Number 0.1160 in 2.946 mm —Nominal
3.0 mm Metric 0.1181 in 3.000 mm —Nominal
#31 Number 0.1200 in 3.048 mm —Nominal
3.1 mm Metric 0.1220 in 3.100 mm —Nominal
1/8 in Fractional 0.1250 in 3.175 mm —Nominal
3.2 mm Metric 0.1260 in 3.200 mm —Nominal
#30 Number 0.1285 in 3.264 mm —Nominal
3.3 mm Metric 0.1299 in 3.300 mm —Nominal
3.4 mm Metric 0.1339 in 3.400 mm —Nominal
#29 Number 0.1360 in 3.454 mm —Nominal
3.5 mm Metric 0.1378 in 3.500 mm —Nominal
#28 Number 0.1405 in 3.569 mm —Nominal
9/64 in Fractional 0.1406 in 3.572 mm —Nominal
3.6 mm Metric 0.1417 in 3.600 mm —Nominal
#27 Number 0.1440 in 3.658 mm —Nominal
3.7 mm Metric 0.1457 in 3.700 mm —Nominal
#26 Number 0.1470 in 3.734 mm —Nominal
#25 Number 0.1495 in 3.797 mm —Nominal
3.8 mm Metric 0.1496 in 3.800 mm —Nominal
#24 Number 0.1520 in 3.861 mm —Nominal
3.9 mm Metric 0.1535 in 3.900 mm —Nominal
#23 Number 0.1540 in 3.912 mm —Nominal
5/32 in Fractional 0.1562 in 3.969 mm —Nominal
#22 Number 0.1570 in 3.988 mm —Nominal
4.0 mm Metric 0.1575 in 4.000 mm —Nominal
#21 Number 0.1590 in 4.039 mm —Nominal
#20 Number 0.1610 in 4.089 mm —Nominal
4.1 mm Metric 0.1614 in 4.100 mm —Nominal
4.2 mm Metric 0.1654 in 4.200 mm —Nominal
#19 Number 0.1660 in 4.216 mm —Nominal
4.3 mm Metric 0.1693 in 4.300 mm —Nominal
#18 Number 0.1695 in 4.305 mm —Nominal
11/64 in Fractional 0.1719 in 4.366 mm —Nominal
#17 Number 0.1730 in 4.394 mm —Nominal
4.4 mm Metric 0.1732 in 4.400 mm —Nominal
#16 Number 0.1770 in 4.496 mm —Nominal
4.5 mm Metric 0.1772 in 4.500 mm —Nominal
#15 Number 0.1800 in 4.572 mm —Nominal
4.6 mm Metric 0.1811 in 4.600 mm —Nominal
#14 Number 0.1820 in 4.623 mm —Nominal
#13 Number 0.1850 in 4.699 mm —Nominal
4.7 mm Metric 0.1850 in 4.700 mm —Nominal
3/16 in Fractional 0.1875 in 4.762 mm —Nominal
4.8 mm Metric 0.1890 in 4.800 mm —Nominal
#12 Number 0.1890 in 4.801 mm —Nominal
#11 Number 0.1910 in 4.851 mm —Nominal
4.9 mm Metric 0.1929 in 4.900 mm —Nominal
#10 Number 0.1935 in 4.915 mm —Nominal
#9 Number 0.1960 in 4.978 mm —Nominal
5.0 mm Metric 0.1969 in 5.000 mm —Nominal
#8 Number 0.1990 in 5.055 mm —Nominal
5.1 mm Metric 0.2008 in 5.100 mm —Nominal
#7 Number 0.2010 in 5.105 mm —Nominal
13/64 in Fractional 0.2031 in 5.159 mm —Nominal
#6 Number 0.2040 in 5.182 mm —Nominal
5.2 mm Metric 0.2047 in 5.200 mm —Nominal
#5 Number 0.2055 in 5.220 mm —Nominal
5.3 mm Metric 0.2087 in 5.300 mm —Nominal
#4 Number 0.2090 in 5.309 mm —Nominal
5.4 mm Metric 0.2126 in 5.400 mm —Nominal
#3 Number 0.2130 in 5.410 mm —Nominal
5.5 mm Metric 0.2165 in 5.500 mm —Nominal
7/32 in Fractional 0.2188 in 5.556 mm —Nominal
5.6 mm Metric 0.2205 in 5.600 mm —Nominal
#2 Number 0.2210 in 5.613 mm —Nominal
5.7 mm Metric 0.2244 in 5.700 mm —Nominal
#1 Number 0.2280 in 5.791 mm —Nominal
5.8 mm Metric 0.2283 in 5.800 mm —Nominal
5.9 mm Metric 0.2323 in 5.900 mm —Nominal
A Letter 0.2340 in 5.944 mm —Nominal
15/64 in Fractional 0.2344 in 5.953 mm —Nominal
6.0 mm Metric 0.2362 in 6.000 mm —Nominal
B Letter 0.2380 in 6.045 mm —Nominal
6.1 mm Metric 0.2402 in 6.100 mm —Nominal
C Letter 0.2420 in 6.147 mm —Nominal
6.2 mm Metric 0.2441 in 6.200 mm —Nominal
D Letter 0.2460 in 6.248 mm —Nominal
6.3 mm Metric 0.2480 in 6.300 mm —Nominal
1/4 in Fractional 0.2500 in 6.350 mm —Nominal
E Letter 0.2500 in 6.350 mm —Nominal
6.4 mm Metric 0.2520 in 6.400 mm —Nominal
6.5 mm Metric 0.2559 in 6.500 mm —Nominal
F Letter 0.2570 in 6.528 mm —Nominal
6.6 mm Metric 0.2598 in 6.600 mm —Nominal
G Letter 0.2610 in 6.629 mm —Nominal
6.7 mm Metric 0.2638 in 6.700 mm —Nominal
17/64 in Fractional 0.2656 in 6.747 mm —Nominal
H Letter 0.2660 in 6.756 mm —Nominal
6.8 mm Metric 0.2677 in 6.800 mm —Nominal
6.9 mm Metric 0.2717 in 6.900 mm —Nominal
I Letter 0.2720 in 6.909 mm —Nominal
7.0 mm Metric 0.2756 in 7.000 mm —Nominal
J Letter 0.2770 in 7.036 mm —Nominal
7.1 mm Metric 0.2795 in 7.100 mm —Nominal
K Letter 0.2810 in 7.137 mm —Nominal
9/32 in Fractional 0.2812 in 7.144 mm —Nominal
7.2 mm Metric 0.2835 in 7.200 mm —Nominal
7.3 mm Metric 0.2874 in 7.300 mm —Nominal
L Letter 0.2900 in 7.366 mm —Nominal
7.4 mm Metric 0.2913 in 7.400 mm —Nominal
M Letter 0.2950 in 7.493 mm —Nominal
7.5 mm Metric 0.2953 in 7.500 mm —Nominal
19/64 in Fractional 0.2969 in 7.541 mm —Nominal
7.6 mm Metric 0.2992 in 7.600 mm —Nominal
N Letter 0.3020 in 7.671 mm —Nominal
7.7 mm Metric 0.3031 in 7.700 mm —Nominal
7.8 mm Metric 0.3071 in 7.800 mm —Nominal
7.9 mm Metric 0.3110 in 7.900 mm —Nominal
5/16 in Fractional 0.3125 in 7.938 mm —Nominal
8.0 mm Metric 0.3150 in 8.000 mm —Nominal
O Letter 0.3160 in 8.026 mm —Nominal
8.1 mm Metric 0.3189 in 8.100 mm —Nominal
8.2 mm Metric 0.3228 in 8.200 mm —Nominal
P Letter 0.3230 in 8.204 mm —Nominal
8.3 mm Metric 0.3268 in 8.300 mm —Nominal
21/64 in Fractional 0.3281 in 8.334 mm —Nominal
8.4 mm Metric 0.3307 in 8.400 mm —Nominal
Q Letter 0.3320 in 8.433 mm —Nominal
8.5 mm Metric 0.3346 in 8.500 mm —Nominal
8.6 mm Metric 0.3386 in 8.600 mm —Nominal
R Letter 0.3390 in 8.611 mm —Nominal
8.7 mm Metric 0.3425 in 8.700 mm —Nominal
11/32 in Fractional 0.3438 in 8.731 mm —Nominal
8.8 mm Metric 0.3465 in 8.800 mm —Nominal
S Letter 0.3480 in 8.839 mm —Nominal
8.9 mm Metric 0.3504 in 8.900 mm —Nominal
9.0 mm Metric 0.3543 in 9.000 mm —Nominal
T Letter 0.3580 in 9.093 mm —Nominal
9.1 mm Metric 0.3583 in 9.100 mm —Nominal
23/64 in Fractional 0.3594 in 9.128 mm —Nominal
9.2 mm Metric 0.3622 in 9.200 mm —Nominal
9.3 mm Metric 0.3661 in 9.300 mm —Nominal
U Letter 0.3680 in 9.347 mm —Nominal
9.4 mm Metric 0.3701 in 9.400 mm —Nominal
9.5 mm Metric 0.3740 in 9.500 mm —Nominal
3/8 in Fractional 0.3750 in 9.525 mm —Nominal
V Letter 0.3770 in 9.576 mm —Nominal
9.6 mm Metric 0.3780 in 9.600 mm —Nominal
9.7 mm Metric 0.3819 in 9.700 mm —Nominal
9.8 mm Metric 0.3858 in 9.800 mm —Nominal
W Letter 0.3860 in 9.804 mm —Nominal
9.9 mm Metric 0.3898 in 9.900 mm —Nominal
25/64 in Fractional 0.3906 in 9.922 mm —Nominal
10.0 mm Metric 0.3937 in 10.000 mm —Nominal
X Letter 0.3970 in 10.084 mm —Nominal
10.1 mm Metric 0.3976 in 10.100 mm —Nominal
10.2 mm Metric 0.4016 in 10.200 mm —Nominal
Y Letter 0.4040 in 10.262 mm —Nominal
10.3 mm Metric 0.4055 in 10.300 mm —Nominal
13/32 in Fractional 0.4062 in 10.319 mm —Nominal
10.4 mm Metric 0.4094 in 10.400 mm —Nominal
Z Letter 0.4130 in 10.490 mm —Nominal
10.5 mm Metric 0.4134 in 10.500 mm —Nominal
10.6 mm Metric 0.4173 in 10.600 mm —Nominal
10.7 mm Metric 0.4213 in 10.700 mm —Nominal
27/64 in Fractional 0.4219 in 10.716 mm —Nominal
10.8 mm Metric 0.4252 in 10.800 mm —Nominal
10.9 mm Metric 0.4291 in 10.900 mm —Nominal
11.0 mm Metric 0.4331 in 11.000 mm —Nominal
11.1 mm Metric 0.4370 in 11.100 mm —Nominal
7/16 in Fractional 0.4375 in 11.112 mm —Nominal
11.2 mm Metric 0.4409 in 11.200 mm —Nominal
11.3 mm Metric 0.4449 in 11.300 mm —Nominal
11.4 mm Metric 0.4488 in 11.400 mm —Nominal
11.5 mm Metric 0.4528 in 11.500 mm —Nominal
29/64 in Fractional 0.4531 in 11.509 mm —Nominal
11.6 mm Metric 0.4567 in 11.600 mm —Nominal
11.7 mm Metric 0.4606 in 11.700 mm —Nominal
11.8 mm Metric 0.4646 in 11.800 mm —Nominal
11.9 mm Metric 0.4685 in 11.900 mm —Nominal
15/32 in Fractional 0.4688 in 11.906 mm —Nominal
12.0 mm Metric 0.4724 in 12.000 mm —Nominal
12.1 mm Metric 0.4764 in 12.100 mm —Nominal
12.2 mm Metric 0.4803 in 12.200 mm —Nominal
12.3 mm Metric 0.4843 in 12.300 mm —Nominal
31/64 in Fractional 0.4844 in 12.303 mm —Nominal
12.4 mm Metric 0.4882 in 12.400 mm —Nominal
12.5 mm Metric 0.4921 in 12.500 mm —Nominal
12.6 mm Metric 0.4961 in 12.600 mm —Nominal
1/2 in Fractional 0.5000 in 12.700 mm —Nominal
12.7 mm Metric 0.5000 in 12.700 mm —Nominal
12.8 mm Metric 0.5039 in 12.800 mm —Nominal
12.9 mm Metric 0.5079 in 12.900 mm —Nominal
13.0 mm Metric 0.5118 in 13.000 mm —Nominal
33/64 in Fractional 0.5156 in 13.097 mm —Nominal
17/32 in Fractional 0.5312 in 13.494 mm —Nominal
35/64 in Fractional 0.5469 in 13.891 mm —Nominal
9/16 in Fractional 0.5625 in 14.287 mm —Nominal
37/64 in Fractional 0.5781 in 14.684 mm —Nominal
19/32 in Fractional 0.5938 in 15.081 mm —Nominal
39/64 in Fractional 0.6094 in 15.478 mm —Nominal
5/8 in Fractional 0.6250 in 15.875 mm —Nominal
41/64 in Fractional 0.6406 in 16.272 mm —Nominal
21/32 in Fractional 0.6562 in 16.669 mm —Nominal
43/64 in Fractional 0.6719 in 17.066 mm —Nominal
11/16 in Fractional 0.6875 in 17.462 mm —Nominal
45/64 in Fractional 0.7031 in 17.859 mm —Nominal
23/32 in Fractional 0.7188 in 18.256 mm —Nominal
47/64 in Fractional 0.7344 in 18.653 mm —Nominal
3/4 in Fractional 0.7500 in 19.050 mm —Nominal
49/64 in Fractional 0.7656 in 19.447 mm —Nominal
25/32 in Fractional 0.7812 in 19.844 mm —Nominal
51/64 in Fractional 0.7969 in 20.241 mm —Nominal
13/16 in Fractional 0.8125 in 20.637 mm —Nominal
53/64 in Fractional 0.8281 in 21.034 mm —Nominal
27/32 in Fractional 0.8438 in 21.431 mm —Nominal
55/64 in Fractional 0.8594 in 21.828 mm —Nominal
7/8 in Fractional 0.8750 in 22.225 mm —Nominal
57/64 in Fractional 0.8906 in 22.622 mm —Nominal
29/32 in Fractional 0.9062 in 23.019 mm —Nominal
59/64 in Fractional 0.9219 in 23.416 mm —Nominal
15/16 in Fractional 0.9375 in 23.812 mm —Nominal
61/64 in Fractional 0.9531 in 24.209 mm —Nominal
31/32 in Fractional 0.9688 in 24.606 mm —Nominal
63/64 in Fractional 0.9844 in 25.003 mm —Nominal
1 in Fractional 1.0000 in 25.400 mm —Nominal

Values are nominal drill diameters. The difference column is calculated from the current finder target; number and letter designations are discrete series, not values generated by a continuous gauge formula.

Comparison and page actions

Selected comparison

Compare Nearby Drill Sizes

Compare selected nominal diameters in one unit at a time. The default line view emphasizes small differences between nearby sizes.

Line view uses a locally scaled axis to reveal small differences. Choose bars when a zero baseline is more important than fine comparison.

Select table rows or run the closest-size finder to compare drill diameters.

How to Read the Drill Bit Size Chart

  • Fractional drills are labeled by inch fractions such as 1/8, 3/16, and 1/4 inch.
  • Number drills run from #80 at the small end to #1 at the large end; a higher number generally means a smaller drill.
  • Letter drills increase from A through Z and fill many gaps between common fractional sizes.
  • Metric drills are labeled directly by nominal diameter in millimeters.

Nominal Drill Size Is Not Finished-Hole Size

A twist drill commonly produces a hole that differs from its nominal diameter. Tool runout, spindle condition, drill wear, chisel-edge behavior, workpiece material, feed, speed, coolant, and breakthrough all matter. Use reaming, boring, or another controlled finishing process when the final diameter or tolerance is critical.

Drill Size Systems and Diameter Conversion

Fractional-inch sizes

Fractional drills use exact inch fractions. The table reduces equivalent fractions and converts each fraction from its canonical rational value rather than a rounded display value.

Number and letter sizes

Number and letter drills are standardized discrete series. Their designations do not follow a simple continuous formula, so every nominal diameter is stored as a verified table value.

Metric sizes

Metric designations state nominal diameter directly in millimeters. This page includes a practical 0.2–13.0 mm reference range at 0.1 mm increments.

Common Drill Size Lookup Examples

#7 drill

A #7 drill has a nominal diameter of 0.2010 in, which converts to 5.105 mm. It is often encountered in machine-shop thread preparation, but thread selection requires a separate tap-drill basis.

1/4-inch target

A 0.2500-inch target has two exact nominal matches in the included systems: 1/4 in and letter E. The finder reports ties rather than discarding one designation.

6.4 mm target

A 6.4 mm metric drill equals approximately 0.2520 in. Compare it with adjacent inch-system sizes before substituting, and confirm that the diameter difference is acceptable.

Choosing Nearest, Larger, or Smaller

Closest size

Use for general substitution when absolute diameter difference is the main criterion and either direction is acceptable.

Equal or larger

Use when an undersized nominal drill would violate the immediate requirement. This does not replace an engineering allowance or clearance specification.

Equal or smaller

Use when the nominal drill must not exceed a maximum size, such as before a controlled finishing operation.

Drill chart vs tap-drill chart

This page compares physical drill diameters. Tap-drill selection additionally depends on thread diameter, pitch, desired thread engagement, tap type, material, and process. Clearance-hole selection is a separate fit decision.

Engineering Basis and Dataset Scope

Independent nominal-diameter cross-reference · fractional 1/64–1 in · number #80–#1 · letter A–Z · metric 0.2–13.0 mm

The table is an independently organized educational cross-reference. It cites controlling standards context without reproducing proprietary drill-length or tolerance tables.

Dataset and Review Details

Publisher
Turn2Engineering
Dataset version
1.0
Values
Nominal diameters
Conversion
1 in = exactly 25.4 mm
CSV rights
Full download disabled pending data-rights review
Known exclusion
Finished-hole tolerances and drill lengths
Published rows
299 nominal sizes

Drill Bit Size Chart FAQs

Both a 1/4-inch fractional drill and a letter E drill have a nominal diameter of 0.2500 inch in the included reference, so they are exact nominal matches.

Use the Nominal Size as a Starting Point

Use the finder to identify the nearest available drill designation, verify the exact diameter difference in the table, and then apply the machining tolerance and finishing process required by the part. For close-tolerance holes, nominal drill selection alone is not a final design decision.

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