Special Tap and Drill Bit Size Calculator
Please use the calculator below to find the best drill bit size needed for any fractional taps, including special taps. After you calculate the drill size, please check the conversion chart below for the closest size. If you need to calculate metric sizes, please check out our Metric Tap Drill Size Calculator. When entering numbers in the calculator, do not enter fractions, enter the corresponding deciamal size only.
For reference, the above calculator is performing the following calculation: Drill Bit Size = Maj Diamater - (.975/Threads Per Inch)
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Drill Size Conversion
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Fraction
(in)
|
Decimal
(in)
|
Wire (#)
Letter (A-Z)
|
Metric
(mm)
|
Fraction
(in)
|
Decimal
(in)
|
Wire (#)
Letter (A-Z)
|
Metric
(mm)
|
Fraction
(in)
|
Decimal
(in)
|
Wire (#)
Letter (A-Z)
|
Metric
(mm)
|
|
|
| |
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0.0098
|
|
0.25
|
|
0.1065
|
36
|
|
|
0.3480
|
S
|
|
|
|
0.0118
|
|
0.30
|
7/64
|
0.1094
|
|
|
|
0.3543
|
|
9.00
|
|
|
0.0135
|
80
|
|
|
0.1100
|
35
|
|
|
0.3580
|
T
|
|
|
|
0.0138
|
|
0.35
|
|
0.1102
|
|
2.80
|
23/64
|
0.3594
|
|
|
|
|
0.0145
|
79
|
|
|
0.1110
|
34
|
|
|
0.3680
|
U
|
|
|
1/64
|
0.0156
|
|
|
|
0.1130
|
33
|
|
|
0.3740
|
|
9.50
|
|
|
0.0157
|
|
0.40
|
|
0.1142
|
|
2.90
|
3/8
|
0.3750
|
|
|
|
|
0.0160
|
78
|
|
|
0.1160
|
32
|
|
|
0.3770
|
V
|
|
|
|
0.0177
|
|
0.45
|
|
0.1181
|
|
3.00
|
|
0.3860
|
W
|
|
|
|
0.0180
|
77
|
|
|
0.1200
|
31
|
|
25/64
|
0.3906
|
|
|
|
|
0.0197
|
|
0.50
|
1/8
|
0.1250
|
|
|
|
0.3937
|
|
10.00
|
|
|
0.0200
|
76
|
|
|
0.1285
|
30
|
|
|
0.3970
|
X
|
|
|
|
0.0210
|
75
|
|
|
0.1360
|
29
|
|
|
0.4040
|
Y
|
|
|
|
0.0217
|
|
0.55
|
|
0.1378
|
|
3.50
|
13/32
|
0.4063
|
|
|
|
|
0.0225
|
74
|
|
|
0.1405
|
28
|
|
|
0.4130
|
Z
|
|
|
|
0.0236
|
|
0.60
|
9/64
|
0.1406
|
|
|
|
0.4134
|
|
10.50
|
|
|
0.0240
|
73
|
|
|
0.1440
|
27
|
|
27/64
|
0.4219
|
|
|
|
|
0.0250
|
72
|
|
|
0.1470
|
26
|
|
|
0.4331
|
|
11.00
|
|
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0.0256
|
|
0.65
|
|
0.1495
|
25
|
|
7/16
|
0.4375
|
|
|
|
|
0.0260
|
71
|
|
|
0.1520
|
24
|
|
|
0.4528
|
|
11.50
|
|
|
0.0276
|
|
0.70
|
|
0.1540
|
23
|
|
29/64
|
0.4531
|
|
|
|
|
0.0280
|
70
|
|
5/32
|
0.1563
|
|
|
15/32
|
0.4688
|
|
|
|
|
0.0292
|
69
|
|
|
0.1570
|
22
|
|
|
0.4724
|
|
12.00
|
|
|
0.0295
|
|
0.75
|
|
0.1575
|
|
4.00
|
31/64
|
0.4844
|
|
|
|
|
0.0310
|
68
|
|
|
0.1590
|
21
|
|
|
0.4921
|
|
12.50
|
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1/32
|
0.0313
|
|
|
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0.1610
|
20
|
|
1/2
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0.5000
|
|
|
|
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0.0315
|
|
0.80
|
|
0.1660
|
19
|
|
|
0.5118
|
|
13.00
|
|
|
0.0320
|
67
|
|
|
0.1695
|
18
|
|
33/64
|
0.5156
|
|
|
|
|
0.0330
|
66
|
|
11/64
|
0.1719
|
|
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17/32
|
0.5313
|
|
|
|
|
0.0335
|
|
0.85
|
|
0.1730
|
17
|
|
|
0.5315
|
|
13.50
|
|
|
0.0350
|
65
|
|
|
0.1770
|
16
|
|
35/64
|
0.5469
|
|
|
|
|
0.0354
|
|
0.90
|
|
0.1772
|
|
4.50
|
|
0.5512
|
|
14.00
|
|
|
0.0360
|
64
|
|
|
0.1800
|
15
|
|
9/16
|
0.5625
|
|
|
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|
0.0370
|
63
|
|
|
0.1820
|
14
|
|
|
0.5709
|
|
14.50
|
|
|
0.0374
|
|
0.95
|
|
0.1850
|
13
|
|
37/64
|
0.5781
|
|
|
|
|
0.0380
|
62
|
|
3/16
|
0.1875
|
|
|
|
0.5905
|
|
15.00
|
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|
0.0390
|
61
|
|
|
0.1890
|
12
|
|
19/32
|
0.5938
|
|
|
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|
0.0394
|
|
1.00
|
|
0.1910
|
11
|
|
39/64
|
0.6094
|
|
|
|
|
0.0400
|
60
|
|
|
0.1935
|
10
|
|
|
0.6102
|
|
15.50
|
|
|
0.0410
|
59
|
|
|
0.1960
|
9
|
|
5/8
|
0.6250
|
|
|
|
|
0.0420
|
58
|
|
|
0.1968
|
|
5.00
|
|
0.6299
|
|
16.00
|
|
|
0.0430
|
57
|
|
|
0.1990
|
8
|
|
41/64
|
0.6406
|
|
|
|
|
0.0433
|
|
1.10
|
|
0.2010
|
7
|
|
|
0.6496
|
|
16.50
|
|
|
0.0465
|
56
|
|
13/64
|
0.2031
|
|
|
21/32
|
0.6563
|
|
|
|
3/64
|
0.0469
|
|
|
|
0.2040
|
6
|
|
|
0.6693
|
|
17.00
|
|
|
0.0472
|
|
1.20
|
|
0.2055
|
5
|
|
43/64
|
0.6719
|
|
|
|
|
0.0512
|
|
1.30
|
|
0.2090
|
4
|
|
11/16
|
0.6875
|
|
|
|
|
0.0520
|
55
|
|
|
0.2130
|
3
|
|
|
0.6890
|
|
17.50
|
|
|
0.0550
|
54
|
|
|
0.2165
|
|
5.50
|
45/64
|
0.7031
|
|
|
|
|
0.0551
|
|
1.40
|
7/32
|
0.2188
|
|
|
|
0.7087
|
|
18.00
|
|
|
0.0591
|
|
1.50
|
|
0.2210
|
2
|
|
23/32
|
0.7188
|
|
|
|
|
0.0595
|
53
|
|
|
0.2280
|
1
|
|
|
0.7283
|
|
18.50
|
|
1/16
|
0.0625
|
|
|
|
0.2340
|
A
|
|
47/64
|
0.7344
|
|
|
|
|
0.0630
|
|
1.60
|
15/64
|
0.2344
|
|
|
|
0.7480
|
|
19.00
|
|
|
0.0635
|
52
|
|
|
0.2362
|
|
6.00
|
3/4
|
0.7500
|
|
|
|
|
0.0669
|
|
1.70
|
|
0.2380
|
B
|
|
49/64
|
0.7656
|
|
|
|
|
0.0670
|
51
|
|
|
0.2420
|
C
|
|
|
0.7677
|
|
19.50
|
|
|
0.0700
|
50
|
|
|
0.2460
|
D
|
|
25/32
|
0.7813
|
|
|
|
|
0.0709
|
|
1.80
|
1/4
|
0.2500
|
E
|
|
|
0.7874
|
|
20.00
|
|
|
0.0730
|
49
|
|
|
0.2559
|
|
6.50
|
51/64
|
0.7969
|
|
|
|
|
0.0748
|
|
1.90
|
|
0.2570
|
F
|
|
|
0.8071
|
|
20.50
|
|
|
0.0760
|
48
|
|
|
0.2610
|
G
|
|
13/16
|
0.8125
|
|
|
|
5/64
|
0.0781
|
|
|
17/64
|
0.2656
|
|
|
|
0.8268
|
|
21.00
|
|
|
0.0785
|
47
|
|
|
0.2660
|
H
|
|
53/64
|
0.8281
|
|
|
|
|
0.0787
|
|
2.00
|
|
0.2720
|
I
|
|
27/32
|
0.8438
|
|
|
|
|
0.0810
|
46
|
|
|
0.2756
|
|
7.00
|
|
0.8465
|
|
21.50
|
|
|
0.0820
|
45
|
|
|
0.2770
|
J
|
|
55/64
|
0.8594
|
|
|
|
|
0.0827
|
|
2.10
|
|
0.2810
|
K
|
|
|
0.8661
|
|
22.00
|
|
|
0.0860
|
44
|
|
9/32
|
0.2813
|
|
|
7/8
|
0.8750
|
|
|
|
|
0.0866
|
|
2.20
|
|
0.2900
|
L
|
|
|
0.8858
|
|
22.50
|
|
|
0.0890
|
43
|
|
|
0.2950
|
M
|
|
57/64
|
0.8906
|
|
|
|
|
0.0906
|
|
2.30
|
|
0.2953
|
|
7.50
|
|
0.9055
|
|
23.00
|
|
|
0.0935
|
42
|
|
19/64
|
0.2969
|
|
|
29/32
|
0.9063
|
|
|
|
3/32
|
0.0938
|
|
|
|
0.3020
|
N
|
|
59/64
|
0.9219
|
|
|
|
|
0.0945
|
|
2.40
|
5/16
|
0.3125
|
|
|
|
0.9252
|
|
23.50
|
|
|
0.0960
|
41
|
|
|
0.3150
|
|
8.00
|
15/16
|
0.9375
|
|
|
|
|
0.0980
|
40
|
|
|
0.3160
|
O
|
|
|
0.9449
|
|
24.00
|
|
|
0.0984
|
|
2.50
|
|
0.3230
|
P
|
|
61/64
|
0.9531
|
|
|
|
|
0.0995
|
39
|
|
21/64
|
0.3281
|
|
|
|
0.9646
|
|
24.50
|
|
|
0.1015
|
38
|
|
|
0.3320
|
Q
|
|
31/32
|
0.9688
|
|
|
|
|
0.1024
|
|
2.60
|
|
0.3346
|
|
8.50
|
|
0.9842
|
|
25.00
|
|
|
0.1040
|
37
|
|
|
0.3390
|
R
|
|
63/64
|
0.9844
|
|
|
|
|
0.1063
|
|
2.70
|
11/32
|
0.3438
|
|
|
1
|
1.0000
|
|
|
| |
|
Fraction
(in)
|
Decimal
(in)
|
Wire (#)
Letter (A-Z)
|
Metric
(mm)
|
Fraction
(in)
|
Decimal
(in)
|
Wire (#)
Letter (A-Z)
|
Metric
(mm)
|
Fraction
(in)
|
Decimal
(in)
|
Wire (#)
Letter (A-Z)
|
Metric
(mm)
|
|
|
| |
|
|
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