7/8 - 9 UNC - Basic Thread Dimensions
| Property | Inch | mm |
|---|---|---|
| Nominal Diameter | 0.875 | 22.225 |
| Pitch (TPI) | 9 | |
| Pitch (Distance) | 0.1111 | 2.822 |
| Pitch Diameter | 0.8028 | 20.391 |
| Minor Diameter | 0.7427 | 18.865 |
| Thread Height | 0.0601 | 1.527 |
| Addendum | 0.0361 | 0.917 |
| Crest (External) Root (Internal) |
0.0139 | 0.353 |
| Tap Drill Size (75% depth) |
0.767 | 19.47 |
| Lead Angle (Single Start) |
2.52° | |
| Thread Family | Unified Coarse Pitch (UNC) | |
| Relevant Standards | ASME B1.1-2003 | |
| Equivalent Metric Thread | M22 |
For more threading data scroll down, or use the Thread Calculator
Table of Content
- Limit of dimensions for all thread classes
- Tap drill sizes
- Cutting conditions for External Threading (Thread Turning & Thread Milling)
- Cutting conditions for Internal Threading (Thread Turning, Thread Milling & Tapping)
- Over wire measurements
7/8 - 9 UNC Possible Thread Classes
7/8 - 9 UNC 1A (External)
* Permisable values for thread Class 1A
| # | Description | Value (Inch) | Value (mm) |
|---|---|---|---|
| es | Allowance | 0.0018 (Ref) | 0.046 (Ref) |
| d | Major Diameter | 0.8524 - 0.8732 | 21.651 - 22.179 |
| d2 | Pitch Diameter | 0.792 - 0.801 | 20.117 - 20.345 |
| d3 | Minor Diameter (UNR Only) | 0.7409 (Ref) | 18.819 (Ref) |
| α | Varation of 30° anngle (+/-) | 0.75° | |
| P | Varation of pitch (+/-) | 0.0026 (Ref) | 0.066 (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 - 9 UNC 2A (External)
* Permisable values for thread Class 2A
| # | Description | Value (Inch) | Value (mm) |
|---|---|---|---|
| es | Allowance | 0.0018 (Ref) | 0.046 (Ref) |
| d | Major Diameter | 0.8593 - 0.8732 | 21.826 - 22.179 |
| d2 | Pitch Diameter | 0.795 - 0.801 | 20.193 - 20.345 |
| d3 | Minor Diameter (UNR Only) | 0.7409 (Ref) | 18.819 (Ref) |
| α | Varation of 30° anngle (+/-) | 0.75° | |
| P | Varation of pitch (+/-) | 0.0017 (Ref) | 0.043 (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 - 9 UNC 3A (External)
* Permisable values for thread Class 3A
| # | Description | Value (Inch) | Value (mm) |
|---|---|---|---|
| es | Allowance | 0 (Ref) | 0 (Ref) |
| d | Major Diameter | 0.8611 - 0.875 | 21.872 - 22.225 |
| d2 | Pitch Diameter | 0.7983 - 0.8028 | 20.277 - 20.391 |
| d3 | Minor Diameter (UNR Only) | 0.7427 (Ref) | 18.865 (Ref) |
| α | Varation of 30° anngle (+/-) | 0.75° | |
| P | Varation of pitch (+/-) | 0.0013 (Ref) | 0.033 (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 - 9 UNC 1B (Internal)
* Permisable values for thread Class 1B
| # | Description | Value (Inch) | Value (mm) |
|---|---|---|---|
| D1 | Minor Diameter | 0.755 - 0.778 | 19.177 - 19.761 |
| D2 | Pitch Diameter | 0.8028 - 0.8145 | 20.391 - 20.688 |
| D | Major Diameter | 0.8750 (Min) | 22.225 (Min) |
| α | Varation of 30° anngle (+/-) | 0.75° | |
| P | Varation of Pitch (+/-) | 0.0034 (Ref) | 0.086 (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 - 9 UNC 2B (Internal)
* Permisable values for thread Class 2B
| # | Description | Value (Inch) | Value (mm) |
|---|---|---|---|
| D1 | Minor Diameter | 0.755 - 0.778 | 19.177 - 19.761 |
| D2 | Pitch Diameter | 0.8028 - 0.8106 | 20.391 - 20.589 |
| D | Major Diameter | 0.8750 (Min) | 22.225 (Min) |
| α | Varation of 30° anngle (+/-) | 0.75° | |
| P | Varation of Pitch (+/-) | 0.0023 (Ref) | 0.058 (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 - 9 UNC 3B (Internal)
* Permisable values for thread Class 3B
| # | Description | Value (Inch) | Value (mm) |
|---|---|---|---|
| D1 | Minor Diameter | 0.7547 - 0.7681 | 19.169 - 19.51 |
| D2 | Pitch Diameter | 0.8028 - 0.8087 | 20.391 - 20.541 |
| D | Major Diameter | 0.8750 (Min) | 22.225 (Min) |
| α | Varation of 30° anngle (+/-) | 0.75° | |
| P | Varation of Pitch (+/-) | 0.0017 (Ref) | 0.043 (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 - 9 UNC
- 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% | 0.796 | 20.21 |
| 60% | 0.788 | 20.02 |
| 65% | 0.781 | 19.84 |
| 70% | 0.774 | 19.66 |
| 75% | 0.767 | 19.47 |
| 80% | 0.759 | 19.29 |
| 85% | 0.752 | 19.11 |
Over Wire Measurements for 7/8 - 9 UNC
* 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 | 0.0561 - 0.1123 | 1.426 - 2.851 |
| Ideal Wire Diameter | 0.0641 | 1.629 |
| Possible Wires From Standard Sets |
* 0.0642 * 0.0722 * 0.077 * 0.0825 * 0.0962 * 0.105 |
* 1.443 * 1.732 * 2.021 * 2.309 * 2.598 |
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!
