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It is useful some time to have some basic thread data sheets. If you are tapping a thread and need to know which drill to use for either the tapping size or the clearance. Never to get one that is near enough always use the right one. Too small a drill means you might snap a tap or too large a one means you have a poor loose thread.

British Association Thread Chart

No

Decimal

TPI

Pitch

Core Dia.

Thread 
Depth

Radius

Hex
A/Flats

Tapping
Size

MM

Letter
or
Number

0

0.2362

25.4

0.0394

0.1887

0.0236

0.0071

0.413

0.2008

5.1

9

1

0.2087

28.2

0.0354

0.1665

0.0213

0.0064

0.365

0.1772

4.5

16

2

0.1850

31.4

0.0319

0.1467

0.0191

0.0057

0.324

0.1575

4.0

22

3

0.1614

34.8

0.0287

0.1266

0.0173

0.0052

0.282

0.1339

3.4

29

4

0.1417

38.5

0.0260

0.1108

0.0156

0.0047

0.248

0.1181

3.0

31

5

0.1260

43.0

0.0232

0.0981

0.0140

0.0042

0.220

0.1043

2.65

37

6

0.1102

47.9

0.0209

0.0849

0.0126

0.0038

0.193

0.0906

2.3

42

7

0.0984

52.9

0.0189

0.0753

0.0114

0.0034

0.172

0.0807

2.05

46

8

0.0866

59.1

0.0169

0.0657

0.0102

0.0031

0.152

0.0709

1.8

50

9

0.0748

65.1

0.0154

0.0565

0.0093

0.0028

0.131

0.0610

1.55

1/16

10

0.0669

72.6

0.0138

0.0504

0.0083

0.0025

0.117

0.0551

1.40

54

11

0.0590

82.0

0.0122

0.0443

0.0073

0.0022

 

0.0472

1.2

56

12

0.0511

90.7

0.0110

0.0378

0.0067

0.0020

 

0.0413

1.05

60

13

0.0472

102.0

0.0098

0.0352

0.0059

0.0018

 

0.0386

0.98

62

14

0.0394

110.0

0.0091

0.0280

0.0055

0.0016

 

0.0315

0.80

1/32

15

0.0354

121.0

0.0083

0.0250

0.0049

0.0015

 

0.0276

0.70

70

16

0.0311

134.0

0.0075

0.0220

0.0045

0.0014

 

0.0236

0.60

73