NOMINAL DIA- INCH

ACTUAL DIA- MM

TPI

1/16"

7.723

28

1/8"

9.728

28

¼"

13.157

19

3/8"

16.662

19

½"

20.995

14

5/8"

22.911

14

¾"

26.441

14

7/8"

30.201

14

1"

33.249

11

1.1/8"

37.897

11

1.1/4"

41.910

11

1.1/2"

47.803

11

1.3/4"

53.746

11

2"

59.614

11

2.1/4"

65.710

11

2.1/2"

75.184

11

2.3/4"

81.534

11

3"

87.884

11

3.1/2"

100.330

11

4"

113.030

11

4.1/2"

125.730

11

5"

138.430

11

5.1/2"

151.130

11

6"

163.830

11

NOMINAL DIA- INCH

ACTUAL DIA- MM

TPI

Plug gauges – only General class
Ring gauges – Class 'A' / Class 'B'
Tolerance for class 'A' rings are close / tighter than Class 'B'. In case of pitch diameter tolerance, Class 'A' tolerance is exactly half the Class 'B' tolerance.

For Plugs - G1/2"
For Rings - G1/2 A
                 G1/2 B