RECOMMENDED TAP DRILL TO USE FOR 75% DEPTH OF THREAD

To Tap This Size Screw Or Bolt:

Use This Drill Bit:

(Closest Fractional:)

Decimal Inches

0-80 NF

3/64"

3/64"

.0469

1-64 NC

#53

-

.0595

1-72 NF

#53

1/16"

.0595

2-56 NC

#50

-

.0700

2-64 NF

#50

-

.0700

3-48 NC

#47

5/64"

.0785

3-56 NF

#45

-

.0820

4-36 NS

#44

-

.0860

4-40 NC

#43

3/32"

.0890

4-48 NF

#42

3/32"

.0935

3mm-0.60mm

2.5mm

-

.0984

1/8-40 NS

#38

-

.1015

5-40 NC

#38

-

.1015

5-44 NF

#37

-

.1040

6-32 NC

#35

7/64"

.1100

6-36 NS

#34

-

.1110

6-40 NF

#33

-

.1130

6-48 NS

#31

-

.1200

4mm-0.70mm

3.4mm

-

.1338

4mm-0.75mm

3.4mm

-

.1338

8-32 NC

#29

-

.1360

8-36 NF

#29

9/64"

.1360

8-40 NS

#28

-

.1405

3/16-24 NS

#26

-

.1470

10-24 NC

#25

5/32"

.1495

3/16-32 NS

#22

-

.1570

10-32 NF

#21

5/32"

.1590

5mm-0.90mm

4.2mm

-

.1653

5mm-0.80mm

4.3mm

-

.1693

12-24 NC

#16

11/64"

.1770

12-28 NF

#14

3/16"

.1820

12-32 NEF

#13

-

.1850

14-20 NS

#10

-

.1935

1/4-20 NC

#7

13/64"

.2010

14-24 NS

#7

-

.2010

6mm-1.00mm

5.2mm

-

.2047

1/4-24 NS

#4

-

.2090

1/4-28 NF

#3

7/32"

.2130

1/4-32 NEF

7/32"

7/32"

.2188

1/4-40 NS

#1

-

.2280

7mm-1.00mm

6.1mm

15/64"

.2401

5/16-18 NC

Ltr.F

17/64"

.2570

8mm-1.25mm

6.9mm

17/64"

.2716

5/16-24 NF

Ltr.I

-

.2720

8mm-1.00mm

7.1mm

-

.2795

5/16-32 NEF

9/32"

9/32"

.2812

9mm-1.25mm

7.9mm

-

.3110

3/8-16 NC

5/16"

5/16"

.3125

 

* These Sizes Are Spark Plug Taps

 

To Tap This Size Screw Or Bolt:

Use This Drill Bit:

(Closest Fractional:)

Decimal Inches

9mm-1.00mm

8.1mm

-

.3189

9mm-0.75mm

8.3mm

-

.3268

3/8-24 NF

Ltr.Q

21/64"

.3320

10mm-1.50mm

8.7mm

-

.3425

10mm-1.25mm

8.9mm

11/32"

.3503

10mm-1.00mm*

9.1mm

-

.3583

7/16-14 NC

Ltr.U

23/64"

.3680

11mm-1.50mm

9.7mm

-

.3818

7/16-20 NF

25/64"

25/64"

.3906

12mm-1.75mm

10.5mm

-

.4133

12mm-1.50mm

10.7mm

27/64"

.4212

1/2-13 NC

27/64"

27/64"

.4219

12mm-1.25mm*

10.9mm

27/64"

.4291

1/2-20 NF

29/64"

29/64"

.4531

1/2-24 NS

29/64"

29/64"

.4531

14mm-2.00mm

12.2mm

-

.4803

9/16-12 NC

31/64"

31/64"

.4844

14mm-1.50mm

12.7mm

-

.4999

14mm-1.25mm*

12.8mm

-

.5039

9/16-18 NF

33/64"

33/64"

.5156

5/8-11 NC

17/32"

17/32"

.5312

16mm-2.00mm

14.2mm

35/64"

.5590

5/8-18 NF

37/64"

37/64"

.5781

16mm-1.50mm

14.7mm

-

.5787

11/16-11 NS

19/32"

19/32"

.5938

18mm-2.50mm

15.8mm

39/64"

.6220

11/16-16 NS

5/8"

5/8"

.6250

3/4-10 NC

21/32"

21/32"

.6562

18mm-1.50mm*

16.8mm

-

.6614

3/4-16 NF

11/16"

11/16"

.6875

20mm-2.50mm

17.8mm

11/16"

.7008

7/8-9 NC

49/64"

49/64"

.7656

7/8-14 NF

13/16"

13/16"

.8125

22mm-1.50mm

20.9mm

-

.8228

7/8-18 NS*

53/64"

53/64"

.8281

24mm-3.00mm

21.4mm

53/64"

.8425

1.8 NC

7/8"

7/8"

.8750

24mm-2.00mm

22.3mm

-

.8779

1.12 NF

59/64"

59/64"

.9219

1-14 NS

15/16"

15/16"

.9375

1 1/8-7 NC

63/64"

63/64"

.9844

1 1/8-12 NF

1 3/64"

1 3/64"

1.0469

1 1/4-7 NC

1 7/64"

1 7/64"

1.1094

1 1/4-12 NF

1 11/64"

1 11/64"

1.1719

1 3/8-6 NC

1 7/32"

1 7/32"

1.2188

1 3/8-12 NF

1 19/64"

1 19/64"

1.2969

1 1/2-6 NC

1 11/32"

1 11/32"

1.3438

1 1/2"-12 NF

1 27/64"

1 27/64"

1.4219

Letter Drill Sizes

This chart shows the diameters of letter gauge drills size A (the smallest) to size Z (the largest).

DrillInchmm
A0.2345.94
B0.2386.05
C0.2426.15
D0.2466.25
E0.2506.35
F0.2576.53
G0.2616.63
H0.2666.76
I0.2726.91
J0.2777.04
K0.2817.14
L0.297.37
M0.2957.49
N0.3027.67
O0.3168.03
P0.3238.20
Q0.3328.43
R0.3398.61
S0.3488.84
T0.3589.09
U0.3689.35
V0.3779.58
W0.3869.80
X0.39710.08
Y0.40410.26
Z0.41310.49


xxx

Tap drill chart