M18 X 1.5 - Basic Thread Dimensions

Property mm Inch
Nominal Diameter 18 0.7087
Pitch (Distance) 1.5 0.0591
Pitch Diameter 17.026 0.6703
Minor Diameter 16.376 0.6447
Thread Height 0.812 0.032
Addendum 0.487 0.0192
Crest (External)
Root (Internal)		 0.188 0.0074
Tap Drill Size
(75% depth)		 16.54 0.651
Lead Angle
(Single Start)		 1.61°
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 - 16 16-UN

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

Table of Content

M18 X 1.5 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 1.5 4g (External)

* Permisable values for thread Class 4g

# Description Value (mm) Value (Inch)
es Allowance 0.032 (Ref) 0.0013 (Ref)
d Major Diameter 17.818 - 17.968 0.7015 - 0.7074
d2 Pitch Diameter 16.904 - 16.994 0.6655 - 0.6691
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.342 0.0074 - 0.0135
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

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M18 X 1.5 4h (External)

* Permisable values for thread Class 4h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 17.85 - 18 0.7028 - 0.7087
d2 Pitch Diameter 16.936 - 17.026 0.6668 - 0.6703
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.342 0.0074 - 0.0135
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

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M18 X 1.5 6e (External)

* Permisable values for thread Class 6e

# Description Value (mm) Value (Inch)
es Allowance 0.067 (Ref) 0.0026 (Ref)
d Major Diameter 17.697 - 17.933 0.6967 - 0.706
d2 Pitch Diameter 16.819 - 16.959 0.6622 - 0.6677
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.378 0.0074 - 0.0149
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

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M18 X 1.5 6g (External)

* Permisable values for thread Class 6g

# Description Value (mm) Value (Inch)
es Allowance 0.032 (Ref) 0.0013 (Ref)
d Major Diameter 17.732 - 17.968 0.6981 - 0.7074
d2 Pitch Diameter 16.854 - 16.994 0.6635 - 0.6691
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.378 0.0074 - 0.0149
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

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M18 X 1.5 6h (External)

* Permisable values for thread Class 6h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 17.764 - 18 0.6994 - 0.7087
d2 Pitch Diameter 16.886 - 17.026 0.6648 - 0.6703
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.378 0.0074 - 0.0149
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

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M18 X 1.5 8e (External)

* Permisable values for thread Class 8e

# Description Value (mm) Value (Inch)
es Allowance 0.067 (Ref) 0.0026 (Ref)
d Major Diameter 17.558 - 17.933 0.6913 - 0.706
d2 Pitch Diameter 16.735 - 16.959 0.6589 - 0.6677
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.431 0.0074 - 0.017
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

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M18 X 1.5 8g (External)

* Permisable values for thread Class 8g

# Description Value (mm) Value (Inch)
es Allowance 0.032 (Ref) 0.0013 (Ref)
d Major Diameter 17.593 - 17.968 0.6926 - 0.7074
d2 Pitch Diameter 16.77 - 16.994 0.6602 - 0.6691
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.431 0.0074 - 0.017
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

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M18 X 1.5 5g4g (External)

* Permisable values for thread Class 5g4g

# Description Value (mm) Value (Inch)
es Allowance 0.032 (Ref) 0.0013 (Ref)
d Major Diameter 17.818 - 17.968 0.7015 - 0.7074
d2 Pitch Diameter 16.882 - 16.994 0.6646 - 0.6691
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.358 0.0074 - 0.0141
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 5h4h (External)

* Permisable values for thread Class 5h4h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 17.85 - 18 0.7028 - 0.7087
d2 Pitch Diameter 16.914 - 17.026 0.6659 - 0.6703
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.358 0.0074 - 0.0141
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 5g6g (External)

* Permisable values for thread Class 5g6g

# Description Value (mm) Value (Inch)
es Allowance 0.032 (Ref) 0.0013 (Ref)
d Major Diameter 17.732 - 17.968 0.6981 - 0.7074
d2 Pitch Diameter 16.882 - 16.994 0.6646 - 0.6691
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.358 0.0074 - 0.0141
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 7g6g (External)

* Permisable values for thread Class 7g6g

# Description Value (mm) Value (Inch)
es Allowance 0.032 (Ref) 0.0013 (Ref)
d Major Diameter 17.732 - 17.968 0.6981 - 0.7074
d2 Pitch Diameter 16.814 - 16.994 0.662 - 0.6691
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.404 0.0074 - 0.0159
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 7h6h (External)

* Permisable values for thread Class 7h6h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 17.764 - 18 0.6994 - 0.7087
d2 Pitch Diameter 16.846 - 17.026 0.6632 - 0.6703
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.404 0.0074 - 0.0159
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 7e6e (External)

* Permisable values for thread Class 7e6e

# Description Value (mm) Value (Inch)
es Allowance 0.067 (Ref) 0.0026 (Ref)
d Major Diameter 17.697 - 17.933 0.6967 - 0.706
d2 Pitch Diameter 16.779 - 16.959 0.6606 - 0.6677
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.404 0.0074 - 0.0159
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 9e8e (External)

* Permisable values for thread Class 9e8e

# Description Value (mm) Value (Inch)
es Allowance 0.067 (Ref) 0.0026 (Ref)
d Major Diameter 17.558 - 17.933 0.6913 - 0.706
d2 Pitch Diameter 16.679 - 16.959 0.6567 - 0.6677
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.463 0.0074 - 0.0182
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 9g8g (External)

* Permisable values for thread Class 9g8g

# Description Value (mm) Value (Inch)
es Allowance 0.032 (Ref) 0.0013 (Ref)
d Major Diameter 17.593 - 17.968 0.6926 - 0.7074
d2 Pitch Diameter 16.714 - 16.994 0.658 - 0.6691
R Root Radius 0.188 (Min) 0.0074 (Min)
C Root Truncation 0.188 - 0.463 0.0074 - 0.0182
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 4H (Internal)

* Permisable values for thread Class 4H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 16.376 - 16.566 0.6447 - 0.6522
D2 Pitch Diameter 17.026 - 17.144 0.6703 - 0.675
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 5H (Internal)

* Permisable values for thread Class 5H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 16.376 - 16.612 0.6447 - 0.654
D2 Pitch Diameter 17.026 - 17.176 0.6703 - 0.6762
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 5G (Internal)

* Permisable values for thread Class 5G

# Description Value (mm) Value (Inch)
EL Allowance 0.032 (Ref) 0.0013 (Ref)
D1 Minor Diameter 16.408 - 16.644 0.646 - 0.6553
D2 Pitch Diameter 17.058 - 17.208 0.6716 - 0.6775
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 6H (Internal)

* Permisable values for thread Class 6H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 16.376 - 16.676 0.6447 - 0.6565
D2 Pitch Diameter 17.026 - 17.216 0.6703 - 0.6778
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 6G (Internal)

* Permisable values for thread Class 6G

# Description Value (mm) Value (Inch)
EL Allowance 0.032 (Ref) 0.0013 (Ref)
D1 Minor Diameter 16.408 - 16.708 0.646 - 0.6578
D2 Pitch Diameter 17.058 - 17.248 0.6716 - 0.6791
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 7H (Internal)

* Permisable values for thread Class 7H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 16.376 - 16.751 0.6447 - 0.6595
D2 Pitch Diameter 17.026 - 17.262 0.6703 - 0.6796
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 7G (Internal)

* Permisable values for thread Class 7G

# Description Value (mm) Value (Inch)
EL Allowance 0.032 (Ref) 0.0013 (Ref)
D1 Minor Diameter 16.408 - 16.783 0.646 - 0.6607
D2 Pitch Diameter 17.058 - 17.294 0.6716 - 0.6809
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

M18 X 1.5 8G (Internal)

* Permisable values for thread Class 8G

# Description Value (mm) Value (Inch)
EL Allowance 0.032 (Ref) 0.0013 (Ref)
D1 Minor Diameter 16.408 - 16.883 0.646 - 0.6647
D2 Pitch Diameter 17.058 - 17.358 0.6716 - 0.6834
D Major Diameter 18 (Min) 0.7087 (Min)
LE Normal Length of Engagement 5.6 - 16 0.2205 - 0.6299

* Back to Thread Class Selection

Tap Drill Sizes for M18 X 1.5

  • 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% 0.666 16.93
60% 0.663 16.83
65% 0.659 16.73
70% 0.655 16.64
75% 0.651 16.54
80% 0.647 16.44
85% 0.643 16.34

Over Wire Measurements for M18 X 1.5


* 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 0.758 - 1.516 0.0298 - 0.0597
Ideal Wire Diameter 0.866 0.0341
Possible Wires
From Standard Sets		 * 0.866
* 1.01
* 1.155
* 1.443

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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