Thread data sheet

Basic Thread Dimensions

Property Inch mm
Nominal Diameter 0.875 22.225
Pitch (TPI)28
Pitch (Distance) 0.0357 0.907
Pitch Diameter 0.8518 21.636
Minor Diameter 0.8325 21.146
Thread Height 0.0193 0.49
Addendum 0.0116 0.295
Crest (External)
Root (Internal)
0.0045 0.114
Tap Drill Size
(75% depth)
0.84 21.34
Lead Angle
(Single Start)
0.76°
Thread Family Unified Constant Pitch 28 TPI (28-UN)
Relevant Standards ASME B1.1-2003
Equivalent MetricThreadM22 X 1

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

Choose the Threading Data you want to explore


7/8 - 28 28-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 - 28 28-UN 2A (External)

* Permisable values for thread Class 2A

# Description Value (Inch) Value (mm)
es Allowance 0.0011 (Ref) 0.028 (Ref)
d Major Diameter 0.8674 - 0.8739 22.032 - 22.197
d2 Pitch Diameter 0.847 - 0.8507 21.514 - 21.608
d3 Minor Diameter
(UNR Only)
0.8314 (Ref) 21.118 (Ref)
α Varation of 30° anngle (+/-) 1.3333°
P Varation of pitch (+/-) 0.0011 (Ref) 0.028 (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 - 28 28-UN 3A (External)

* Permisable values for thread Class 3A

# Description Value (Inch) Value (mm)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 0.8685 - 0.875 22.06 - 22.225
d2 Pitch Diameter 0.849 - 0.8518 21.565 - 21.636
d3 Minor Diameter
(UNR Only)
0.8325 (Ref) 21.146 (Ref)
α Varation of 30° anngle (+/-) 1.3333°
P Varation of pitch (+/-) 0.0008 (Ref) 0.02 (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 - 28 28-UN 2B (Internal)

* Permisable values for thread Class 2B

# Description Value (Inch) VValue (mm)
D1 Minor Diameter 0.836 - 0.845 21.234 - 21.463
D2 Pitch Diameter 0.8518 - 0.8566 21.636 - 21.758
D Major Diameter 0.8750 (Min) 22.225 (Min)
α Varation of 30° anngle (+/-) 1.3333°
P Varation of Pitch (+/-) 0.0014 (Ref) 0.036 (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 - 28 28-UN 3B (Internal)

* Permisable values for thread Class 3B

# Description Value (Inch) VValue (mm)
D1 Minor Diameter 0.8363 - 0.8426 21.242 - 21.402
D2 Pitch Diameter 0.8518 - 0.8554 21.636 - 21.727
D Major Diameter 0.8750 (Min) 22.225 (Min)
α Varation of 30° anngle (+/-) 1.3333°
P Varation of Pitch (+/-) 0.001 (Ref) 0.025 (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 - 28 28-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% 0.849 21.58
60% 0.847 21.52
65% 0.845 21.46
70% 0.843 21.40
75% 0.840 21.34
80% 0.838 21.28
85% 0.836 21.22

Over Wire Measurements for 7/8 - 28 28-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 0.018 - 0.0361 0.458 - 0.916
Ideal Wire Diameter 0.0206 0.524
Possible Wires
From Standard Sets
* 0.018
* 0.0193
* 0.0206
* 0.0214
* 0.0222
* 0.0241
* 0.0262
* 0.0289
* 0.462
* 0.52
* 0.577
* 0.722
* 0.866

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 - 28 28-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=0.035714285714286 INCH, L=0.35714285714286 INCH)
(APPLICATION - EXTERNAL TURNING, TOWARDS CHUCK, RH TOOL, RH THREAD)
(FEED - 17 PASSES, FLANK, CONSTANT VOLUME)
(FINISH PASS - 0.0003 INCH)
(WITH CHAMFER -  NO)
G28 U0 W0
T0101 G99 G97 S437 M03
G00 Z5.1
X 32.4 M08
G76 P010060 Q8 R0.008
G76 X21.112 Z-9.071 P556 Q133 F0.907 R0.00 
G28 U0 W0
M09
M30
%
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