Nominal
Diameter

Major
Diameter
Inch

Major
Diameter
mm

Tapping
Drill Size
mm

TPI

Pitch
mm

1 1/16" - 8-UN

1.0625

26.987

24.000

8

3.175

1 1/8" - 8-UN

1.1250

28.575

25.500

8

3.175

1 3/16" - 8-UN

1.1875

30.162

27.200

8

3.175

1 1/4" - 8-UN

1.2500

31.750

28.800

8

3.175

1 5/16" - 8-UN

1.3125

33.337

30.300

8

3.175

1 3/8" - 8-UN

1.3750

34.925

31.900

8

3.175

1 7/16" - 8-UN

1.4375

36.512

33.500

8

3.175

1 1/2" - 8-UN

1.5000

38.100

35.100

8

3.175

1 9/16" - 8-UN

1.5625

39.688

36.700

8

3.175

1 5/8" - 8-UN

1.6250

41.275

38.300

8

3.175

1 11/16" - 8-UN

1.6875

42.862

39.900

8

3.175

1 3/4" - 8-UN

1.7500

44.450

41.400

8

3.175

1 13/16" - 8-UN

1.8125

46.037

43.000

8

3.175

1 7/8" - 8-UN

1.8750

47.625

44.600

8

3.175

1 15/16" - 8-UN

1.9375

49.212

46.200

8

3.175

2" - 8-UN

2.0000

50.800

47.800

8

3.175

2 1/8" - 8-UN

2.1250

53.975

51.000

8

3.175

2 1/4" - 8-UN

2.2500

57.150

54.100

8

3.175

2 3/8" - 8-UN

2.3750

60.325

57.300

8

3.175

2 1/2" - 8-UN

2.5000

63.500

60.500

8

3.175

2 5/8" - 8-UN

2.6250

66.675

64.700

8

3.175

2 3/4" - 8-UN

2.7500

69.850

66.800

8

3.175

2 7/8" - 8-UN

2.8750

73.025

70.000

8

3.175

3" - 8-UN

3.0000

76.200

73.200

8

3.175

3 1/8" - 8-UN

3.1250

79.375

76.400

8

3.175

3 1/4" - 8-UN

3.2500

82.550

79.500

8

3.175

3 3/8" - 8-UN

3.3750

85.725

82.700

8

3.175

3 1/2" - 8-UN

3.5000

88.900

85.900

8

3.175

3 5/8" - 8-UN

3.6250

92.075

89.000

8

3.175

3 3/4" - 8-UN

3.7500

95.250

92.300

8

3.175

3 7/8" - 8-UN

3.8750

98.425

95.400

8

3.175

4" - 8-UN

4.0000

101.600

98.600

8

3.175