M18 X 2 - Basic Thread Dimensions

Property mm Inch
Nominal Diameter 18 0.7087
Pitch (Distance) 2 0.0787
Pitch Diameter 16.701 0.6575
Minor Diameter 15.835 0.6234
Thread Height 1.083 0.0426
Addendum 0.65 0.0256
Crest (External)
Root (Internal)		 0.25 0.0098
Tap Drill Size
(75% depth)		 16.05 0.632
Lead Angle
(Single Start)		 2.18°
Thread Family Metric Fine Pitch (MF)
Relevant Standards ISO 68-1, ISO 9651-1, ISO 965-2, ISO 261,DIN 13
Equivalent Inch Thread11/16 - 12 12-UN

For more threading data scroll down, or use the Thread Calculator

Table of Content

M18 X 2 Possible Thread Classes

External Threads

Choose tolerance class: 4g, 4h, 6e, 6g, 6h, 8e, 8g, 5g4g, 5h4h, 5g6g, 7g6g, 7h6h, 7e6e, 9e8e, 9g8g

Metric ISO External Thread - Tolerance sketch

Internal Threads

Choose tolerance class: 4H, 5H, 5G, 6H, 6G, 7H, 7G, 8G

Metric ISO Internal Thread - Tolerance sketch

M18 X 2 4g (External)

* Permisable values for thread Class 4g

# Description Value (mm) Value (Inch)
es Allowance 0.038 (Ref) 0.0015 (Ref)
d Major Diameter 17.782 - 17.962 0.7001 - 0.7072
d2 Pitch Diameter 16.563 - 16.663 0.6521 - 0.656
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.44 0.0098 - 0.0173
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

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M18 X 2 4h (External)

* Permisable values for thread Class 4h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 17.82 - 18 0.7016 - 0.7087
d2 Pitch Diameter 16.601 - 16.701 0.6536 - 0.6575
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.44 0.0098 - 0.0173
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

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M18 X 2 6e (External)

* Permisable values for thread Class 6e

# Description Value (mm) Value (Inch)
es Allowance 0.071 (Ref) 0.0028 (Ref)
d Major Diameter 17.649 - 17.929 0.6948 - 0.7059
d2 Pitch Diameter 16.47 - 16.63 0.6484 - 0.6547
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.485 0.0098 - 0.0191
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

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M18 X 2 6g (External)

* Permisable values for thread Class 6g

# Description Value (mm) Value (Inch)
es Allowance 0.038 (Ref) 0.0015 (Ref)
d Major Diameter 17.682 - 17.962 0.6961 - 0.7072
d2 Pitch Diameter 16.503 - 16.663 0.6497 - 0.656
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.485 0.0098 - 0.0191
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

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M18 X 2 6h (External)

* Permisable values for thread Class 6h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 17.72 - 18 0.6976 - 0.7087
d2 Pitch Diameter 16.541 - 16.701 0.6512 - 0.6575
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.485 0.0098 - 0.0191
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

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M18 X 2 8e (External)

* Permisable values for thread Class 8e

# Description Value (mm) Value (Inch)
es Allowance 0.071 (Ref) 0.0028 (Ref)
d Major Diameter 17.479 - 17.929 0.6881 - 0.7059
d2 Pitch Diameter 16.38 - 16.63 0.6449 - 0.6547
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.545 0.0098 - 0.0215
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

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M18 X 2 8g (External)

* Permisable values for thread Class 8g

# Description Value (mm) Value (Inch)
es Allowance 0.038 (Ref) 0.0015 (Ref)
d Major Diameter 17.512 - 17.962 0.6894 - 0.7072
d2 Pitch Diameter 16.413 - 16.663 0.6462 - 0.656
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.545 0.0098 - 0.0215
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

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M18 X 2 5g4g (External)

* Permisable values for thread Class 5g4g

# Description Value (mm) Value (Inch)
es Allowance 0.038 (Ref) 0.0015 (Ref)
d Major Diameter 17.782 - 17.962 0.7001 - 0.7072
d2 Pitch Diameter 16.538 - 16.663 0.6511 - 0.656
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.46 0.0098 - 0.0181
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 5h4h (External)

* Permisable values for thread Class 5h4h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 17.82 - 18 0.7016 - 0.7087
d2 Pitch Diameter 16.576 - 16.701 0.6526 - 0.6575
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.46 0.0098 - 0.0181
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 5g6g (External)

* Permisable values for thread Class 5g6g

# Description Value (mm) Value (Inch)
es Allowance 0.038 (Ref) 0.0015 (Ref)
d Major Diameter 17.682 - 17.962 0.6961 - 0.7072
d2 Pitch Diameter 16.538 - 16.663 0.6511 - 0.656
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.46 0.0098 - 0.0181
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 7g6g (External)

* Permisable values for thread Class 7g6g

# Description Value (mm) Value (Inch)
es Allowance 0.038 (Ref) 0.0015 (Ref)
d Major Diameter 17.682 - 17.962 0.6961 - 0.7072
d2 Pitch Diameter 16.463 - 16.663 0.6481 - 0.656
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.513 0.0098 - 0.0202
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

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M18 X 2 7h6h (External)

* Permisable values for thread Class 7h6h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 17.72 - 18 0.6976 - 0.7087
d2 Pitch Diameter 16.501 - 16.701 0.6496 - 0.6575
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.513 0.0098 - 0.0202
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 7e6e (External)

* Permisable values for thread Class 7e6e

# Description Value (mm) Value (Inch)
es Allowance 0.071 (Ref) 0.0028 (Ref)
d Major Diameter 17.649 - 17.929 0.6948 - 0.7059
d2 Pitch Diameter 16.43 - 16.63 0.6469 - 0.6547
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.513 0.0098 - 0.0202
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 9e8e (External)

* Permisable values for thread Class 9e8e

# Description Value (mm) Value (Inch)
es Allowance 0.071 (Ref) 0.0028 (Ref)
d Major Diameter 17.479 - 17.929 0.6881 - 0.7059
d2 Pitch Diameter 16.315 - 16.63 0.6423 - 0.6547
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.584 0.0098 - 0.023
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 9g8g (External)

* Permisable values for thread Class 9g8g

# Description Value (mm) Value (Inch)
es Allowance 0.038 (Ref) 0.0015 (Ref)
d Major Diameter 17.512 - 17.962 0.6894 - 0.7072
d2 Pitch Diameter 16.348 - 16.663 0.6436 - 0.656
R Root Radius 0.25 (Min) 0.0098 (Min)
C Root Truncation 0.25 - 0.584 0.0098 - 0.023
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 4H (Internal)

* Permisable values for thread Class 4H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 15.835 - 16.071 0.6234 - 0.6327
D2 Pitch Diameter 16.701 - 16.833 0.6575 - 0.6627
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 5H (Internal)

* Permisable values for thread Class 5H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 15.835 - 16.135 0.6234 - 0.6352
D2 Pitch Diameter 16.701 - 16.871 0.6575 - 0.6642
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 5G (Internal)

* Permisable values for thread Class 5G

# Description Value (mm) Value (Inch)
EL Allowance 0.038 (Ref) 0.0015 (Ref)
D1 Minor Diameter 15.873 - 16.173 0.6249 - 0.6367
D2 Pitch Diameter 16.739 - 16.909 0.659 - 0.6657
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 6H (Internal)

* Permisable values for thread Class 6H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 15.835 - 16.21 0.6234 - 0.6382
D2 Pitch Diameter 16.701 - 16.913 0.6575 - 0.6659
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 6G (Internal)

* Permisable values for thread Class 6G

# Description Value (mm) Value (Inch)
EL Allowance 0.038 (Ref) 0.0015 (Ref)
D1 Minor Diameter 15.873 - 16.248 0.6249 - 0.6397
D2 Pitch Diameter 16.739 - 16.951 0.659 - 0.6674
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 7H (Internal)

* Permisable values for thread Class 7H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 15.835 - 16.31 0.6234 - 0.6421
D2 Pitch Diameter 16.701 - 16.966 0.6575 - 0.668
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 7G (Internal)

* Permisable values for thread Class 7G

# Description Value (mm) Value (Inch)
EL Allowance 0.038 (Ref) 0.0015 (Ref)
D1 Minor Diameter 15.873 - 16.348 0.6249 - 0.6436
D2 Pitch Diameter 16.739 - 17.004 0.659 - 0.6694
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

M18 X 2 8G (Internal)

* Permisable values for thread Class 8G

# Description Value (mm) Value (Inch)
EL Allowance 0.038 (Ref) 0.0015 (Ref)
D1 Minor Diameter 15.873 - 16.473 0.6249 - 0.6485
D2 Pitch Diameter 16.739 - 17.074 0.659 - 0.6722
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 8 - 24 0.315 - 0.9449

* Back to Thread Class Selection

Tap Drill Sizes for M18 X 2

  • If not specified, assume a thread depth of 75%.
  • You can learn more about thread depth in tapping here.
  • To get the tap drill size in other depths, use our Tap Drill Size Calculator .
Thread Depth Tap Drill Size (Inch) Tap Drill Size (mm)
55% 0.652 16.57
60% 0.647 16.44
65% 0.642 16.31
70% 0.637 16.18
75% 0.632 16.05
80% 0.627 15.92
85% 0.622 15.79

Over Wire Measurements for M18 X 2


* OverWire is a measuring method to obatin the pitch diameter of threads. It is mostly used when a manufacturer does not have a Go/Nogo gauge for a thread. You can learn more about it here

mm Inch
Permissible Wire Diameter Range 1.01 - 2.021 0.0398 - 0.0796
Ideal Wire Diameter 1.155 0.0455
Possible Wires
From Standard Sets		 * 1.01
* 1.155
* 1.443
* 1.732
* 2.021
 * 0.0642
* 0.0722
* 0.077

Once you knoe your wire diameter, you need to find out what is the premissable Measurement for your pitch diameter (Depending on the class). Use our Over Wire Calculator to find out!


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