Metric Threads - DiracDelta Science & Engineering Encyclopedia

Metric Threads

The most commonly used type of general-purpose screw thread, one of the first international standards agreed when the International Organization for Standardization was set up in 1947.

Metric Coarse

Size [mm]

Pitch [mm]

Tap drill [mm]

Clearance drill [mm]

1.0

0.25

0.75

1.1

0.25

0.85

1.2

0.25

0.95

1.4

0.3

1.1

1.6

0.35

1.25

1.8

1.7

0.35

1.3

1.8

0.35

1.45

0.4

1.6

2.4

2.2

0.45

1.75

2.5

0.45

2.05

2.90

3.0

0.5

2.5

3.40

3.5

0.6

2.9

3.90

4.0

0.7

3.3

4.50

4.5

0.75

3.7

0.8

4.2

5.50

6.60

1.25

6.8

9.0

1.25

7.8

1.5

8.5

12.0

1.5

9.5

1.75

10.2

14.0

16.0

18.0

2.5

15.5

2.5

17.5

22.0

2.5

19.5

25.0

27.0

30.0

3.5

26.5

33.0

3.5

29.5

40.0

Metric Fine

Size [mm]

Pitch [mm]

Tap drill [mm]

Clearance drill [mm]

.35

3.6

3.5

4.5

5.5

.75

5.25

.75

6.25

.75

7.25

7.5

.75

9.25

1.25

8.8

.75

11.25

1.5

10.5

1.25

12.8

1.5

12.5

1.5

14.5

1.5

18.5

1.5

20.5

1.5

22.5

1.5

24.5

1.5

25.5

1.5

26.5

1.5

28.5

Reference

ISO 68-1: ISO general purpose screw threads - Basic profile - Metric screw threads.

ISO 261, titled ISO general purpose metric screw threads-General plan, is an international standard that defines a detailed list of preferred combinations of outer diameter D and pitch P for ISO metric screw threads.

ISO 262, titled ISO general purpose metric screw threads-Selected sizes for screws, bolts and nuts, defines a shorter list of thread dimensions - a subset of the combinations listed in ISO 261