Thread data sheet

Basic Thread Dimensions

Property Inch mm
Nominal Diameter 0.875 22.225
Pitch (TPI)20
Pitch (Distance) 0.05 1.27
Pitch Diameter 0.8425 21.4
Minor Diameter 0.8155 20.714
Thread Height 0.0271 0.688
Addendum 0.0162 0.411
Crest (External)
Root (Internal)
0.0063 0.16
Tap Drill Size
(75% depth)
0.826 20.99
Lead Angle
(Single Start)
1.08°
Thread Family Unified Constant Pitch 20 TPI (20-UN)
Relevant Standards ASME B1.1-2003
Equivalent MetricThreadM22 X 1.5

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

Choose the Threading Data you want to explore


7/8 - 20 20-UNPossible Thread Classes

External Threads

2A, 3A

Metric ISO External Thread - Tolerance sketch

Internal Threads

2B, 3B

Metric ISO Internal Thread - Tolerance sketch

7/8 - 20 20-UN 2A (External)

* Permisable values for thread Class 2A

# Description Value (Inch) Value (mm)
es Allowance 0.0013 (Ref) 0.033 (Ref)
d Major Diameter 0.8656 - 0.8737 21.986 - 22.192
d2 Pitch Diameter 0.837 - 0.8412 21.26 - 21.366
d3 Minor Diameter
(UNR Only)
0.8142 (Ref) 20.681 (Ref)
α Varation of 30° anngle (+/-) 1.1667°
P Varation 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


7/8 - 20 20-UN 3A (External)

* Permisable values for thread Class 3A

# Description Value (Inch) Value (mm)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 0.8669 - 0.875 22.019 - 22.225
d2 Pitch Diameter 0.8393 - 0.8425 21.318 - 21.4
d3 Minor Diameter
(UNR Only)
0.8155 (Ref) 20.714 (Ref)
α Varation of 30° anngle (+/-) 1.1667°
P Varation 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


7/8 - 20 20-UN 2B (Internal)

* Permisable values for thread Class 2B

# Description Value (Inch) VValue (mm)
D1 Minor Diameter 0.821 - 0.832 20.853 - 21.133
D2 Pitch Diameter 0.8425 - 0.848 21.4 - 21.539
D Major Diameter 0.8750 (Min) 22.225 (Min)
α Varation of 30° anngle (+/-) 1.1667°
P Varation 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


7/8 - 20 20-UN 3B (Internal)

* Permisable values for thread Class 3B

# Description Value (Inch) VValue (mm)
D1 Minor Diameter 0.8209 - 0.8287 20.851 - 21.049
D2 Pitch Diameter 0.8425 - 0.8466 21.4 - 21.504
D Major Diameter 0.8750 (Min) 22.225 (Min)
α Varation of 30° anngle (+/-) 1.1667°
P Varation 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 7/8 - 20 20-UN

  • 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% 0.839 21.32
60% 0.836 21.23
65% 0.833 21.15
70% 0.830 21.07
75% 0.826 20.99
80% 0.823 20.90
85% 0.820 20.82

Over Wire Measurements for 7/8 - 20 20-UN


* 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

Inch mm
Permissible Wire Diameter Range 0.0253 - 0.0505 0.642 - 1.283
Ideal Wire Diameter 0.0289 0.733
Possible Wires
From Standard Sets
* 0.0262
* 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 7/8 - 20 20-UN

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=0.875 INCH, P=0.05 INCH, L=0.5 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 U0 W0
T0101 G99 G97 S437 M03
G00 Z5.1
X 32.4 M08
G76 P010060 Q13 R0.013
G76 X20.667 Z-12.7 P779 Q186 F1.27 R0.00 
G28 U0 W0
M09
M30
%
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