5/8 - 18 UNF : Thread Dimensions (Machining Doctor) (2024)

Table of Contents
Basic Thread Dimensions 5/8 - 18 UNFPossible Thread Classes 5/8 - 18 UNF 2A (External) 5/8 - 18 UNF 3A (External) 5/8 - 18 UNF 2B (Internal) 5/8 - 18 UNF 3B (Internal) Tap Drill Sizes for 5/8 - 18 UNF Over Wire Measurements for 5/8 - 18 UNF CNC Gcode Program for Turning of 5/8 - 18 UNF CNC Gcode Program for Thread Milling of 5/8 - 18 UNF Our Top Picks ThreaDoctor: Advanced thread Calculator Machinability Chart True position calculator and formulas Surface Finish: Calculators, Convertors, and Charts Hardness Conversion Calculator

Basic Thread Dimensions

PropertyInchmm
Nominal Diameter0.62515.875
Pitch (TPI)18
Pitch (Distance)0.05561.412
Pitch Diameter0.588914.958
Minor Diameter0.558814.194
Thread Height0.03010.765
Addendum0.0180.457
Crest (External)
Root (Internal)		0.00690.175
Tap Drill Size
(75% depth)		0.57114.5
Lead Angle
(Single Start)		1.72°
Thread FamilyUnified Fine Pitch (UNF)
Relevant StandardsASME B1.1-2003
Equivalent MetricThreadM16 X 1.5
5/8 - 18 UNF : Thread Dimensions (Machining Doctor) (1)

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

Choose the Threading Data you want to explore

Tolerance Classes

Thread Milling Gcode

Turning Gcode

Over Wire

Tap Drill Size

5/8 - 18 UNFPossible Thread Classes

External Threads

2A, 3A

5/8 - 18 UNF : Thread Dimensions (Machining Doctor) (12)

Internal Threads

2B, 3B

5/8 - 18 UNF : Thread Dimensions (Machining Doctor) (13)

5/8 - 18 UNF 2A (External)

* Permisable values for thread Class 2A

#DescriptionValue (Inch)Value (mm)
esAllowance0.0013 (Ref)0.033 (Ref)
dMajor Diameter0.615 - 0.623715.621 - 15.842
d2Pitch Diameter0.5833 - 0.587614.816 - 14.925
d3Minor Diameter
(UNR Only)		0.5576 (Ref)14.163 (Ref)
αVaration of 30° anngle (+/-)1.0833°
PVaration of pitch (+/-)0.0012 (Ref)0.03 (Ref)

* Values are calculated for Length of engagement of 5xPitch. For calculations of different engagement length use the Thread Calculator'

* Back to Thread Class Selection

5/8 - 18 UNF 3A (External)

* Permisable values for thread Class 3A

#DescriptionValue (Inch)Value (mm)
esAllowance0 (Ref)0 (Ref)
dMajor Diameter0.6163 - 0.62515.654 - 15.875
d2Pitch Diameter0.5857 - 0.588914.877 - 14.958
d3Minor Diameter
(UNR Only)		0.5588 (Ref)14.194 (Ref)
αVaration of 30° anngle (+/-)1.0833°
PVaration of pitch (+/-)0.0009 (Ref)0.023 (Ref)

* Values are calculated for Length of engagement of 5xPitch. For calculations of different engagement length use the Thread Calculator'

* Back to Thread Class Selection

5/8 - 18 UNF 2B (Internal)

* Permisable values for thread Class 2B

#DescriptionValue (Inch)VValue (mm)
D1Minor Diameter0.565 - 0.57814.351 - 14.681
D2Pitch Diameter0.5889 - 0.594414.958 - 15.098
DMajor Diameter0.6250 (Min)15.875 (Min)
αVaration of 30° anngle (+/-)1.0833°
PVaration of Pitch (+/-)0.0016 (Ref)0.041 (Ref)

* Values are calculated for Length of engagement of 5xPitch. For calculations of different engagement length use the Thread Calculator

* Back to Thread Class Selection

5/8 - 18 UNF 3B (Internal)

* Permisable values for thread Class 3B

#DescriptionValue (Inch)VValue (mm)
D1Minor Diameter0.5649 - 0.57314.348 - 14.554
D2Pitch Diameter0.5889 - 0.593114.958 - 15.065
DMajor Diameter0.6250 (Min)15.875 (Min)
αVaration of 30° anngle (+/-)1.0833°
PVaration of Pitch (+/-)0.0012 (Ref)0.03 (Ref)

* Values are calculated for Length of engagement of 5xPitch. For calculations of different engagement length use the Thread Calculator

* Back to Thread Class Selection

Tap Drill Sizes for 5/8 - 18 UNF

  • 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 DepthTap Drill Size (Inch)Tap Drill Size (mm)
55%0.58514.87
60%0.58214.77
65%0.57814.68
70%0.57414.59
75%0.57114.50
80%0.56714.41
85%0.56414.32

Over Wire Measurements for 5/8 - 18 UNF

5/8 - 18 UNF : Thread Dimensions (Machining Doctor) (14)

* 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

Inchmm
Permissible Wire Diameter Range0.0281 - 0.05620.713 - 1.427
Ideal Wire Diameter0.03210.815
Possible Wires
From Standard Sets		* 0.0289
* 0.722
* 0.866
* 1.01
* 1.155

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 5/8 - 18 UNF

The below sample Gcode is configured for:

5/8 - 18 UNF : Thread Dimensions (Machining Doctor) (15)
  • 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 ThreadTurningGcodeGenerator 

%O0100(MACHINING DOCTOR - THREADING CNC PROGRAM)(CONTROLER - FANUC A)(THREAD - )(D=0.625 INCH, P=0.056 INCH, L=0.556 INCH)(APPLICATION - EXTERNAL TURNING, TOWARDS CHUCK, RH TOOL, RH THREAD)(FEED - 17 PASSES, FLANK, CONSTANT VOLUME)(FINISH PASS - 0.0005 INCH)(WITH CHAMFER - NO)G28 U0G28 U0T0100G99 G97 S1833 M03G00 Z5.1G00 X19.9 M08G76 P010060 Q13 R0G76 X14 Z-14 P866 Q207 F1 RG28 U0G28 U0M09M30(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.)%

CNC Gcode Program for Thread Milling of 5/8 - 18 UNF

The below sample Gcode is configured for:

5/8 - 18 UNF : Thread Dimensions (Machining Doctor) (16)
  • 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 ThreadMillingGcodeGenerator 


%O0101(WWW.MACHININGDOCTOR.COM - THREADMILLING PROGRAM)(CONTROLER - FANUC)(THREAD - MAJOR DIAM.=0.625 INCH, PITCH=0.055555555555556 INCH, LENGTH=0.55555555555556 INCH)(APPLICATION - INTERNAL, RH THREAD, CLIMB MILLING)(CUTTER DIAM=0.3125 [SINGLE TOOTH])(CUTTER COMPENSATION D=0 - TOOLPATH FOR TOOL CENTER)N1 M06 T1G54G90 G40 G17 G94 G21G00 X0 Y0 S3667 M03G43 H1 Z25.4 M08(M-CODE "THROUGH COOLANT ON")(PASS 1 / 1)G90 G01 Z-14.2875 F2032G91 G01 G41 D1 X1.9844 Y-1.9844 F559G03 X1.9844 Y1.9844 Z0.1764 I0 J1.9844 F140G03 Z1.4111 I-3.9688 J0 F279G03 Z1.4111 I-3.9688 J0G03 Z1.4111 I-3.9688 J0G03 Z1.4111 I-3.9688 J0G03 Z1.4111 I-3.9688 J0G03 Z1.4111 I-3.9688 J0G03 Z1.4111 I-3.9688 J0G03 Z1.4111 I-3.9688 J0G03 Z1.4111 I-3.9688 J0G03 Z1.4111 I-3.9688 J0G03 Z1.4111 I-3.9688 J0G03 X-1.9844 Y1.9844 Z0.1764 I-1.9844 J0G01 G40 X-1.9844 Y-1.9844 F2032G90 G00 Z25.4M30(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.)%

Our Top Picks

  • ThreaDoctor: Advanced thread Calculator

  • Machinability Chart

  • True position calculator and formulas

  • Surface Finish: Calculators, Convertors, and Charts

  • Hardness Conversion Calculator

5/8 - 18 UNF : Thread Dimensions (Machining Doctor) (2024)
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