Nominal
Diameter

Major
Diameter
Inch

Major
Diameter
mm

Tapping
Drill Size
mm

TPI

Pitch
mm

N 12 - 32 UNEF

0.216

5.486

4.80

32

0.794

1/4" - 32 UNEF

0.250

6.350

5.70

32

0.794

5/16" - 32 UNEF

0.313

7.938

7.25

32

0.794

3/8" - 32 UNEF

0.375

9.525

8.85

32

0.794

7/16" - 28 UNEF

0.438

11.112

10.35

28

0.907

1/2" - 28 UNEF

0.500

12.700

11.80

28

0.907

9/16" - 24 UNEF

0.563

14.288

13.40

24

1.058

5/8" - 24 UNEF

0.625

15.875

15.00

24

1.058

11/16" - 24 UNEF

0.688

17.462

16.60

24

1.058

3/4" - 20 UNEF

0.750

19.050

18.00

20

1.270

13/16" - 20 UNEF

0.813

20.638

19.60

20

1.270

7/8" - 20 UNEF

0.875

22.225

21.15

20

1.270

15/16" - 20 UNEF

0.938

23.812

22.70

20

1.270

1" - 20 UNEF

1.000

25.400

24.30

20

1.270

1 1/16" - 18 UNEF

1.063

26.988

25.80

18

1.411

1 1/8" - 18 UNEF

1.125

28.575

27.35

18

1.411

1 1/4" - 18 UNEF

1.250

31.750

30.55

18

1.411

1 5/16" - 18 UNEF

1.313

33.338

32.10

18

1.411

1 3/8" - 18 UNEF

1.375

34.925

33.70

18

1.411

1 7/16" - 18 UNEF

1.438

36.512

35.30

18

1.411

1 1/2" - 18 UNEF

1.500

38.100

36.90

18

1.411

1 9/16" - 18 UNEF

1.563

39.688

38.55

18

1.411

1 5/8" - 18 UNEF

1.625

41.275

40.10

18

1.411

1 11/16" - 18 UNEF

1.688

42.862

41.60

18

1.411