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ISO metric coarse vs fine screw thread Fittings

Date:Apr 11, 2020

The ISO metric screw threads are the most commonly used type of general-purpose screw thread worldwide, The "M" designation for metric screws indicates the nominal outer diameter of the screw thread, in millimeter. two types of thread pitch coarse and fine screw thread. 

 

ISO 261 specifies a detailed list of preferred combinations of outer diameter D and pitch P for ISO metric screw threads. The 1st choice column follows (approximately) the R10 series from ISO 3, while the 2nd choice column are rounded off values from the R20 series from ISO 3.

ISO 262 specifies a shorter list of thread dimensions – a subset of ISO 261.

ISO 262 selected sizes for screws, bolts and nuts


Nominal diameter
D(mm)

Pitch
P(mm)

1st
choice

2nd
choice

Coarse

Fine

1


0.25

0.2

1.2


0.25

0.2


1.4

0.3

0.2

1.6


0.35

0.2


1.8

0.35

0.2

2


0.4

0.25

2.5


0.45

0.35

3


0.5

0.35


3.5

0.6

0.35

4


0.7

0.5



0.8

0.5


5.5DIN13
&ISO[5]

0.9

0.5



1

0.75


7

1

0.75



1.25

1or0.75

10


1.5

1.25or1

12


1.75

1.5or1.25


14

2

1.5

16


2

1.5


|18

2.5

2or1.5

20


2.5

2or1.5


22

2.5

2or1.5

24


3

2


27

3

2

30


3.5

2


33

3.5

2

36


4

3


39

4

3

42


4.5

3


45

4.5

3

48


5

3


52

5

4

56


5.5

4


|60

5.5

4

64


6

4

Spanner (wrench) sizes mm

Below are some common spanner (wrench) sizes for metric screw threads. Hex head widths (width across flats, spanner size) are for DIN 934 hex nuts and hex head bolts. Other (usually smaller) sizes may occur for reasons of weight and cost reduction.

 
Thread

 
Hex nut & bolt

 
Socket head 
cap screw

  
 • Button head cap 
screw 
 • Flat head counter- 
sunk cap screw

 
Set screw (Grub screw)

Size

ISO

DIN




M1

-

2.5

-

-

-

M1.2

-

3

-

-

-

M1.4

-

3

1.25

-

0.7

M1.6

3.2

3.2

1.5

0.9

0.7

M2

4

4

1.5

1.25

0.9

M2.5

5

5

2

1.5

1.3

M3

5.5

5.5

2.5

2

1.5

M3.5

6

6

-

-

-

M4

7

7

3

2.5

2

M5

8

8

4

3

2.5

M6

10

10

5

4

3

M7

11

11

-

-

-

M8

13

13

6

5

4

M10

16

17

8

6

5

M12

18

19

10

8

6

M14

21

22

10

-

-

M16

24

24

14

10

8

M18

27

27

14

12

-

M20

30

30

17

12

10

M22

34

32

17

14

-

M24

36

36

19

14

12

M27

41

41

19

17

14

M30

46

46

22

17

14

M33

50

50

24

-

-

M36

55

55

27

-

-

M39

60

60

-

-

-

M42

65

65

32

-

-

M45

70

70

-

-

-

M48

75

75

36

-

-

M52

80

80

36

-

-

M56

85

85

41

-

-

M60

90

90

-

-

-

M64

95

95

46

-

-


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