Screw & Bolt Threads Up  

American Standard Screw Gauges

The sizes in the first column that are not followed by an inch mark are American Standard Screw gauges. Shading indicates sizes no longer in use or whose use is discouraged by standards organizations. See this table for diameters of tap drills.

The NS series is a catch-all category for threads which have the American Standard form, but whose pitches are not in the National Coarse or National Fine series.

The tap drill sizes are listed in the order in which the tpi are listed in the previous column.

Gage and
Fractional
 Sizes

Major diam.
(inches)

Clearance
Drill

NC & UNC
tpi

Tap Drill
for UNC

NF & UNF
tpi

Tap Drill
for UNF

NEF

NS

Tap drill
for NS

Nut Size

0000

 

#73

160

164

 

 

 

 

 

 

000

 

#63

120

#71

 

 

 

 

 

332

00

 

#55

90

#65

 

 

 

 

 

332

0

0.060

#52

80

364

 

 

 

532

1

0.073

#48

64

#52

72

#53

 

56

#54

532

2

0.086

#43

56

#50

64

#50

 

316

3

0.099

#38

48

#47

56

#45

 

316

4

0.112

#33

40

#43

48

#42

 

32,36

45,44

5

0.125

#30

40

#39

44

#37

 

36

40

6

0.138

#28

32

#36

40

#33

 

36

34

516

7

0.151

 

 

30,32,36

31,31,
18

516

8

0.164

#19

32

#29

36

#29

 

30,
40

30,28

1132

9

0.177

 

 

24,30,32

29,27,
26

1132

10

0.190

#11

24

#25

32

#21

 

28,30

23,22

38

12

0.216

 

24

 

28

 

 

32

13

716

14

0.242

D

 

 

 

 

 

20,24

10,7

716

0.250

″ or E

20

#7

28

#3

32

24,27,32

4,3,732

716

16

0.268

 

 

18, 20, 22

732″,2

18

0.294

 

 

18, 20

B,D

916

516

0.3125

O

18

F

24

I

32

20, 27, 32

1764″,
J,
932

916

20

0.320

 

 

 

 

 

 

16, 18, 20

G,1764″,I

58

22

0.346

 

 

 

 

 

 

16, 18

932″,L

58

24

0.372

 

 

 

 

 

 

16, 18

516″,O

58

38

0.375

V

16

516

24

Q

32

20, 27

 

58

26

0.398

Y

 

 

 

 

 

14, 16

2164″,R

1116

28

0.424

716

 

 

 

 

 

14, 16

T,2364

1116

716

0.4375

716

14

U

20

2564

28

24, 27

 

 

30

0.450

2964

 

 

 

 

 

14, 16

V,2564

78

0.5000 

13 (see note 1)

2764

20

2964

28

12, 24, 27

 

 

12

 

 

 

 

 

 

916

0.5625

916

12

3164

18

3364

24

27

 

 

58

0.6250

58

11

1732

18

3764

24

12,
27

 

 

1116

 0.68753

1116

 

 

 

 

24

 

 

 

0.7500

 

10

2132

16

 

20

12,
27

 

118

78

0.8750

 

9

4964

14

 

20

12,
18,
27

 

1516

1″

1.0000

 

8

78

14

 

20

12,
27

 

1″

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Copyright 2005 -  S. B. EglI