Tapping Drill Tables


Tapping Drill Tables

The tapping drills given in the following pages include millimetre sizes for the convenience of those who are working in or intend to work predominantly in metric units.

Drills have been selected from standard sizes which, when used with reasonable care, will produce holes within the minor diameter limits shown.

From those drills the larger sizes are recommended to facilitate ease of tapping.

As a guide to relative clearances, index figures adjacent to the drill size show the difference between the nominal drill and minimum minor diameters.


ISO Metric Coarse Pitch Series

Thread Size and Pitch
Minor Diameter of nut thread (A)
Tapping Drill Sizes for Commercial Tapping

Maximum

Minimum

Recommended

Alternatives

mm

mm

mm

mm

Inch

mm

M1.6 x 0.35

1.321

1.221

1.303

3/640

1.251

M2 x 0.4

1.679

1.567

1.654

1/161

1.601

M2.5 x 0.45

2.138

2.013

2.103

No. 469

2.051

M3 x 0.5

2.599

2.459

2.553

No. 410

2.501

M4 x 0.7

3.422

3.242

3.406

No. 301

3.302

M5 x 0.8

4.334

4.134

4.306

No. 193

4.202

M6 x 1.00

5.133

4.917

5.107

No. 92

5.003

M8 x 1.25

6.912

6.647

6.9010

17/644

6.806

M10 x 1.5

8.676

8.376

8.609

Q2

8.505

M12 x 1.75

10.441

10.105

10.4011

13/328

10.204

M16 x 2.00

14.210

13.835

14.006

35/642

-

M20 x 2.5

17.744

17.294

17.508

11/167

-

M24 x 3.0

21.252

20.752

21.0010

53/6411

-

M30 x 3.5

26.771

26.211

26.5011

13/6415

-

M36x 4.0

32.270

31.670

32.0013

117/6419

-


The small index figures show the theoretical clearance in thousandths of an inch above the minimum minor diameter of the nut thread.

Letter and wire gauge drills are obsolescent and are being replaced by metric sizes.


British Standard Whitworth – BSW

Thread Size and Pitch per inch
Minor Diameter of nut thread (A)
Tapping Drill Sizes for Commercial Tapping

Maximum

Minimum

Recommended

Alternatives


Inch

Inch

Inch

mm

Inch

1/8 - 40

0.1020

0.0930

397

2.557

405

3/16 - 24

0.1474

0.1341

2710

3.7012

286

1/4 - 20

0.2030

0.1860

910

5.0011

107    123

5/16 - 18

0.2594

0.2413

1/49

6.4011

D5    C1

3/8 - 16

0.3145

0.2950

N7

7.708

19/642    S2

7/16 - 14

0.3674

0.3461

T12

9.1012

Y11    X4

1/2 - 12

0.4169

0.3932

13/3213

10.4013

-

9/16 - 12

0.4794

0.4557

15/3213

12.007

-

5/8 - 11

0.5338

0.5086

17/3223

13.5023

33/647

3/4 - 10

0.6490

0.6220

41/6419

16.2517

5/83

7/8 - 9

0.7620

0.7328

3/417

19.0015

47/642

1 - 8

0.8720

0.8400

55/6419

22.0026

27/321

1 1/8 - 7

0.9776

0.9420

31/3217

24.5022

6 1/6411

1 1/4 - 7

1.1026

1.0670

13/3227

27.5016

1 5/6411

1 1/2 - 6

1.3269

1.2866

1 5/1626

33.0012

1 19/6411

1 3/4 - 5

1.5408

1.4938

1 17/3237

38.5022

1 33/6420

2 - 4.5

1.7668

1.7154

1 3/435

44.5037

1 47/6420

(A) From AS B47 - normal and medium classes.


The small index figures show the theoretical clearance in thousandths of an inch above the minimum minor diameter of the nut thread.

Letter and wire gauge drills are obsolescent and are being replaced by metric sizes.

Tapping Drill Tables.pdf