M1.8 - Basic Thread Dimensions

Property mm Inch
Nominal Diameter 1.8 0.0709
Pitch (Distance) 0.35 0.0138
Pitch Diameter 1.573 0.0619
Minor Diameter 1.421 0.0559
Thread Height 0.189 0.0074
Addendum 0.114 0.0045
Crest (External)
Root (Internal)
0.044 0.0017
Tap Drill Size
(75% depth)
1.46 0.057
Lead Angle
(Single Start)
4.05°
Thread Family Metric Coarse Pitch (MC)
Relevant Standards ISO 68-1, ISO 9651-1, ISO 965-2, ISO 261,DIN 13
Equivalent Inch Thread#1 - 72 UNF

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

Table of Content


M1.8 Possible Thread Classes

External Threads

Choose tolerance class: 4g, 4h, 6g, 6h, 5g4g, 5h4h, 5g6g, 7g6g, 7h6h

Metric ISO External Thread - Tolerance sketch

Internal Threads

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

Metric ISO Internal Thread - Tolerance sketch

M1.8 4g (External)

* Permisable values for thread Class 4g

# Description Value (mm) Value (Inch)
es Allowance 0.019 (Ref) 0.0007 (Ref)
d Major Diameter 1.728 - 1.781 0.068 - 0.0701
d2 Pitch Diameter 1.514 - 1.554 0.0596 - 0.0612
R Root Radius 0.044 (Min) 0.0017 (Min)
C Root Truncation 0.044 - 0.093 0.0017 - 0.0037
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 4h (External)

* Permisable values for thread Class 4h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 1.747 - 1.8 0.0688 - 0.0709
d2 Pitch Diameter 1.533 - 1.573 0.0604 - 0.0619
R Root Radius 0.044 (Min) 0.0017 (Min)
C Root Truncation 0.044 - 0.093 0.0017 - 0.0037
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

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M1.8 6g (External)

* Permisable values for thread Class 6g

# Description Value (mm) Value (Inch)
es Allowance 0.019 (Ref) 0.0007 (Ref)
d Major Diameter 1.696 - 1.781 0.0668 - 0.0701
d2 Pitch Diameter 1.491 - 1.554 0.0587 - 0.0612
R Root Radius 0.044 (Min) 0.0017 (Min)
C Root Truncation 0.044 - 0.107 0.0017 - 0.0042
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

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M1.8 6h (External)

* Permisable values for thread Class 6h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 1.715 - 1.8 0.0675 - 0.0709
d2 Pitch Diameter 1.51 - 1.573 0.0594 - 0.0619
R Root Radius 0.044 (Min) 0.0017 (Min)
C Root Truncation 0.044 - 0.107 0.0017 - 0.0042
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 5g4g (External)

* Permisable values for thread Class 5g4g

# Description Value (mm) Value (Inch)
es Allowance 0.019 (Ref) 0.0007 (Ref)
d Major Diameter 1.728 - 1.781 0.068 - 0.0701
d2 Pitch Diameter 1.504 - 1.554 0.0592 - 0.0612
R Root Radius 0.044 (Min) 0.0017 (Min)
C Root Truncation 0.044 - 0.099 0.0017 - 0.0039
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 5h4h (External)

* Permisable values for thread Class 5h4h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 1.747 - 1.8 0.0688 - 0.0709
d2 Pitch Diameter 1.523 - 1.573 0.06 - 0.0619
R Root Radius 0.044 (Min) 0.0017 (Min)
C Root Truncation 0.044 - 0.099 0.0017 - 0.0039
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 5g6g (External)

* Permisable values for thread Class 5g6g

# Description Value (mm) Value (Inch)
es Allowance 0.019 (Ref) 0.0007 (Ref)
d Major Diameter 1.696 - 1.781 0.0668 - 0.0701
d2 Pitch Diameter 1.504 - 1.554 0.0592 - 0.0612
R Root Radius 0.044 (Min) 0.0017 (Min)
C Root Truncation 0.044 - 0.099 0.0017 - 0.0039
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 7g6g (External)

* Permisable values for thread Class 7g6g

# Description Value (mm) Value (Inch)
es Allowance 0.019 (Ref) 0.0007 (Ref)
d Major Diameter 1.696 - 1.781 0.0668 - 0.0701
d2 Pitch Diameter 1.474 - 1.554 0.058 - 0.0612
R Root Radius 0.044 (Min) 0.0017 (Min)
C Root Truncation 0.044 - 0.116 0.0017 - 0.0046
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 7h6h (External)

* Permisable values for thread Class 7h6h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 1.715 - 1.8 0.0675 - 0.0709
d2 Pitch Diameter 1.493 - 1.573 0.0588 - 0.0619
R Root Radius 0.044 (Min) 0.0017 (Min)
C Root Truncation 0.044 - 0.116 0.0017 - 0.0046
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 4H (Internal)

* Permisable values for thread Class 4H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 1.421 - 1.484 0.0559 - 0.0584
D2 Pitch Diameter 1.573 - 1.626 0.0619 - 0.064
D Major Diameter 1.8 (Min) 0.0709 (Min)
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 5H (Internal)

* Permisable values for thread Class 5H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 1.421 - 1.501 0.0559 - 0.0591
D2 Pitch Diameter 1.573 - 1.64 0.0619 - 0.0646
D Major Diameter 1.8 (Min) 0.0709 (Min)
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 5G (Internal)

* Permisable values for thread Class 5G

# Description Value (mm) Value (Inch)
EL Allowance 0.019 (Ref) 0.0007 (Ref)
D1 Minor Diameter 1.44 - 1.52 0.0567 - 0.0598
D2 Pitch Diameter 1.592 - 1.659 0.0627 - 0.0653
D Major Diameter 1.8 (Min) 0.0709 (Min)
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 6H (Internal)

* Permisable values for thread Class 6H

# Description Value (mm) Value (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 1.421 - 1.521 0.0559 - 0.0599
D2 Pitch Diameter 1.573 - 1.658 0.0619 - 0.0653
D Major Diameter 1.8 (Min) 0.0709 (Min)
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


M1.8 6G (Internal)

* Permisable values for thread Class 6G

# Description Value (mm) Value (Inch)
EL Allowance 0.019 (Ref) 0.0007 (Ref)
D1 Minor Diameter 1.44 - 1.54 0.0567 - 0.0606
D2 Pitch Diameter 1.592 - 1.677 0.0627 - 0.066
D Major Diameter 1.8 (Min) 0.0709 (Min)
LE Normal Length of Engagement 0.8 - 2.6 0.0315 - 0.1024

* Back to Thread Class Selection


Tap Drill Sizes for M1.8

  • 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% 0.061 1.55
60% 0.060 1.53
65% 0.059 1.50
70% 0.058 1.48
75% 0.057 1.46
80% 0.057 1.44
85% 0.056 1.41

Over Wire Measurements for M1.8


* 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 0.177 - 0.354 0.007 - 0.0139
Ideal Wire Diameter 0.202 0.008
Possible Wires
From Standard Sets
* 0.202
* 0.231
* 0.26
* 0.289
* 0.346
* 0.0072
* 0.008
* 0.009
* 0.0103
* 0.0116
* 0.012
* 0.0131

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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