Thread data sheet

Basic Thread Dimensions

Property mm Inch
Nominal Diameter 8 0.315
Pitch (Distance) 1.25 0.0492
Pitch Diameter 7.188 0.283
Minor Diameter 6.647 0.2617
Thread Height 0.677 0.0267
Addendum 0.406 0.016
Crest (External)
Root (Internal)		 0.156 0.0061
Tap Drill Size
(75% depth)		 6.78 0.267
Lead Angle
(Single Start)		 3.17°
Thread Family Metric Coarse Pitch (MC)
Relevant Standards ISO 68-1, ISO 9651-1, ISO 965-2, ISO 261,DIN 13
Equivalent InchThread5/16 - 20 20-UN

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

Choose the Threading Data you want to explore

Unified Inch Thread Classes

Tolerance Classes

Thread Milling CNC program

Thread Milling Gcode

Turning Gcode

Over Wire

Tap Drill Size

Unified Inch Thread Classes

Tolerance Classes

Thread Milling Gcode

Turning Gcode

Over Wire

Tap Drill Size

M8Possible Thread Classes

External Threads

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

Metric ISO External Thread - Tolerance sketch

Internal Threads

4H, 5H, 5G, 6H, 6G, 7H, 7G, 8G

Metric ISO Internal Thread - Tolerance sketch

M8 4g (External)

* Permisable values for thread Class 4g

# Description Value (mm) Value (Inch)
es Allowance 0.028 (Ref) 0.0011 (Ref)
d Major Diameter 7.84 - 7.972 0.3087 - 0.3139
d2 Pitch Diameter 7.085 - 7.16 0.2789 - 0.2819
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.285 0.0061 - 0.0112
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 4h (External)

* Permisable values for thread Class 4h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 7.868 - 8 0.3098 - 0.315
d2 Pitch Diameter 7.113 - 7.188 0.28 - 0.283
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.285 0.0061 - 0.0112
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 6e (External)

* Permisable values for thread Class 6e

# Description Value (mm) Value (Inch)
es Allowance 0.063 (Ref) 0.0025 (Ref)
d Major Diameter 7.725 - 7.937 0.3041 - 0.3125
d2 Pitch Diameter 7.007 - 7.125 0.2759 - 0.2805
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.316 0.0061 - 0.0124
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 6g (External)

* Permisable values for thread Class 6g

# Description Value (mm) Value (Inch)
es Allowance 0.028 (Ref) 0.0011 (Ref)
d Major Diameter 7.76 - 7.972 0.3055 - 0.3139
d2 Pitch Diameter 7.042 - 7.16 0.2772 - 0.2819
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.316 0.0061 - 0.0124
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 6h (External)

* Permisable values for thread Class 6h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 7.788 - 8 0.3066 - 0.315
d2 Pitch Diameter 7.07 - 7.188 0.2783 - 0.283
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.316 0.0061 - 0.0124
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 8e (External)

* Permisable values for thread Class 8e

# Description Value (mm) Value (Inch)
es Allowance 0.063 (Ref) 0.0025 (Ref)
d Major Diameter 7.602 - 7.937 0.2993 - 0.3125
d2 Pitch Diameter 6.935 - 7.125 0.273 - 0.2805
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.361 0.0061 - 0.0142
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 8g (External)

* Permisable values for thread Class 8g

# Description Value (mm) Value (Inch)
es Allowance 0.028 (Ref) 0.0011 (Ref)
d Major Diameter 7.637 - 7.972 0.3007 - 0.3139
d2 Pitch Diameter 6.97 - 7.16 0.2744 - 0.2819
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.361 0.0061 - 0.0142
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 5g4g (External)

* Permisable values for thread Class 5g4g

# Description Value (mm) Value (Inch)
es Allowance 0.028 (Ref) 0.0011 (Ref)
d Major Diameter 7.84 - 7.972 0.3087 - 0.3139
d2 Pitch Diameter 7.065 - 7.16 0.2781 - 0.2819
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.3 0.0061 - 0.0118
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 5h4h (External)

* Permisable values for thread Class 5h4h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 7.868 - 8 0.3098 - 0.315
d2 Pitch Diameter 7.093 - 7.188 0.2793 - 0.283
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.3 0.0061 - 0.0118
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 5g6g (External)

* Permisable values for thread Class 5g6g

# Description Value (mm) Value (Inch)
es Allowance 0.028 (Ref) 0.0011 (Ref)
d Major Diameter 7.76 - 7.972 0.3055 - 0.3139
d2 Pitch Diameter 7.065 - 7.16 0.2781 - 0.2819
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.3 0.0061 - 0.0118
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 7g6g (External)

* Permisable values for thread Class 7g6g

# Description Value (mm) Value (Inch)
es Allowance 0.028 (Ref) 0.0011 (Ref)
d Major Diameter 7.76 - 7.972 0.3055 - 0.3139
d2 Pitch Diameter 7.01 - 7.16 0.276 - 0.2819
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.337 0.0061 - 0.0133
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 7h6h (External)

* Permisable values for thread Class 7h6h

# Description Value (mm) Value (Inch)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 7.788 - 8 0.3066 - 0.315
d2 Pitch Diameter 7.038 - 7.188 0.2771 - 0.283
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.337 0.0061 - 0.0133
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 7e6e (External)

* Permisable values for thread Class 7e6e

# Description Value (mm) Value (Inch)
es Allowance 0.063 (Ref) 0.0025 (Ref)
d Major Diameter 7.725 - 7.937 0.3041 - 0.3125
d2 Pitch Diameter 6.975 - 7.125 0.2746 - 0.2805
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.337 0.0061 - 0.0133
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 9e8e (External)

* Permisable values for thread Class 9e8e

# Description Value (mm) Value (Inch)
es Allowance 0.063 (Ref) 0.0025 (Ref)
d Major Diameter 7.602 - 7.937 0.2993 - 0.3125
d2 Pitch Diameter 6.889 - 7.125 0.2712 - 0.2805
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.387 0.0061 - 0.0152
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 9g8g (External)

* Permisable values for thread Class 9g8g

# Description Value (mm) Value (Inch)
es Allowance 0.028 (Ref) 0.0011 (Ref)
d Major Diameter 7.637 - 7.972 0.3007 - 0.3139
d2 Pitch Diameter 6.924 - 7.16 0.2726 - 0.2819
R Root Radius 0.156 (Min) 0.0061 (Min)
C Root Truncation 0.156 - 0.387 0.0061 - 0.0152
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 4H (Internal)

* Permisable values for thread Class 4H

# Description Value (mm) VValue (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 6.647 - 6.817 0.2617 - 0.2684
D2 Pitch Diameter 7.188 - 7.288 0.283 - 0.2869
D Major Diameter 8 (Min) 0.315 (Min)
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 5H (Internal)

* Permisable values for thread Class 5H

# Description Value (mm) VValue (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 6.647 - 6.859 0.2617 - 0.27
D2 Pitch Diameter 7.188 - 7.313 0.283 - 0.2879
D Major Diameter 8 (Min) 0.315 (Min)
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 5G (Internal)

* Permisable values for thread Class 5G

# Description Value (mm) VValue (Inch)
EL Allowance 0.028 (Ref) 0.0011 (Ref)
D1 Minor Diameter 6.675 - 6.887 0.2628 - 0.2711
D2 Pitch Diameter 7.216 - 7.341 0.2841 - 0.289
D Major Diameter 8 (Min) 0.315 (Min)
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 6H (Internal)

* Permisable values for thread Class 6H

# Description Value (mm) VValue (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 6.647 - 6.912 0.2617 - 0.2721
D2 Pitch Diameter 7.188 - 7.348 0.283 - 0.2893
D Major Diameter 8 (Min) 0.315 (Min)
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 6G (Internal)

* Permisable values for thread Class 6G

# Description Value (mm) VValue (Inch)
EL Allowance 0.028 (Ref) 0.0011 (Ref)
D1 Minor Diameter 6.675 - 6.94 0.2628 - 0.2732
D2 Pitch Diameter 7.216 - 7.376 0.2841 - 0.2904
D Major Diameter 8 (Min) 0.315 (Min)
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 7H (Internal)

* Permisable values for thread Class 7H

# Description Value (mm) VValue (Inch)
EL Allowance 0 (Ref) 0 (Ref)
D1 Minor Diameter 6.647 - 6.982 0.2617 - 0.2749
D2 Pitch Diameter 7.188 - 7.388 0.283 - 0.2909
D Major Diameter 8 (Min) 0.315 (Min)
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 7G (Internal)

* Permisable values for thread Class 7G

# Description Value (mm) VValue (Inch)
EL Allowance 0.028 (Ref) 0.0011 (Ref)
D1 Minor Diameter 6.675 - 7.01 0.2628 - 0.276
D2 Pitch Diameter 7.216 - 7.416 0.2841 - 0.292
D Major Diameter 8 (Min) 0.315 (Min)
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

M8 8G (Internal)

* Permisable values for thread Class 8G

# Description Value (mm) VValue (Inch)
EL Allowance 0.028 (Ref) 0.0011 (Ref)
D1 Minor Diameter 6.675 - 7.1 0.2628 - 0.2795
D2 Pitch Diameter 7.216 - 7.466 0.2841 - 0.2939
D Major Diameter 8 (Min) 0.315 (Min)
LE Normal Length of Engagement 4 - 12 0.1575 - 0.4724

* Back to Thread Class Selection

Tap Drill Sizes for M8

  • 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% 0.280 7.11
60% 0.277 7.03
65% 0.273 6.94
70% 0.270 6.86
75% 0.267 6.78
80% 0.264 6.70
85% 0.261 6.62

Over Wire Measurements for M8


* 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 0.631 - 1.263 0.0249 - 0.0497
Ideal Wire Diameter 0.722 0.0284
Possible Wires
From Standard Sets		 * 0.722
* 0.866
* 1.01
* 1.155
 * 0.0262
* 0.0289

Once you know 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!

CNC Gcode Program for Turning of M8

The below sample Gcode is configured for:

  • Fanuc Controller
  • External RH Thread
  • Right hand tool, machining towards the chuck
  • Flank Infeed method with contant volume
  • Flank Infeed method with contant volume
  • Cutting conditions for steel
  • Default number of passes

You can configure all the above parameters and much more in our Thread Turning Gcode Generator 


%
O0100
(MACHINING DOCTOR - THREADING CNC PROGRAM)
(CONTROLER - FANUC A)
(THREAD - D=8 MM, P=1.25 MM, L=12.5 MM)
(APPLICATION - EXTERNAL TURNING, TOWARDS CHUCK, RH TOOL, RH THREAD)
(FEED - 7 PASSES, FLANK, CONSTANT VOLUME)
(FINISH PASS - 0.027 MM)
(WITH CHAMFER -  NO)
G28 U0 W0
T0101 G99 G97 S3979 M03
G00 Z5.0
X 10.4 M08
G76 P010060 Q27 R0.027
G76 X6.466 Z-12.5 P767 Q280 F1.25 R0.00 
G28 U0 W0
M09
M30
%

CNC Gcode Program for Thread Milling of M8

The below sample Gcode is configured for:

  • Fanuc Controller
  • Internal RH Thread
  • Climb Milling
  • Cutter diameter: 70% of the thread diameter
  • Single tooth Thread Mill cutter
  • Cutting conditions for steel
  • One radial pass

You can configure all the above parameters and much more in our Thread Milling Gcode Generator 


%
O101
(WWW.MACHININGDOCTOR.COM - THREADMILLING PROGRAM)
(CONTROLER - FANUC)
(THREAD - D=8 MM, P=1.25 MM, L=12.5 MM)
(APPLICATION - INTERNAL, RH THREAD, CLIMB MILLING)
(CUTTER - D=4 [SINGLE TOOTH])
N1 M06 T1
G54
G90 G40 G17 G94 G21
G00 X0 Y0 S7958 M03
G43 H1 Z20.0 M08
(M-CODE "THROUGH COOLANT ON")
(PASS 1 / 1)
G90 G01 Z-12.656 F2000
G91 G01 G41 D1 X1.0 Y-1.0 F1194
G03 X1.0 Y1.0 Z0.156 I0 J1.0 F299
G03 Z1.25 I-2.0 J0 F597
G03 Z1.25 I-2.0 J0
G03 Z1.25 I-2.0 J0
G03 Z1.25 I-2.0 J0
G03 Z1.25 I-2.0 J0
G03 Z1.25 I-2.0 J0
G03 Z1.25 I-2.0 J0
G03 Z1.25 I-2.0 J0
G03 Z1.25 I-2.0 J0
G03 Z1.25 I-2.0 J0
G03 X-1.0 Y1.0 Z0.156 I-1.0 J0
G01 G40 X-1.0 Y-1.0 F2000
G90 G00 Z20.0
M30
(PLEASE NOTE THIS GCODE HAS NOT BEEN TESTED ON YOUR MACHINE AND SETUP. WE CANNOT GUARANTEE ITS ACCURACY OR COMPATIBILITY. NOTE THAT YOU ARE USING IT AT YOUR OWN RISK, AND WE SHALL NOT BE HELD LIABLE FOR ANY DAMAGES OR LOSSES ARISING FROM THE USE OF THIS PROGRAM.)
%

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