UNC / UNF - unified national thread
The most common types of UN (Unified National) thread are:
- UNC – Unified National Coarse Thread, comparable with the ISO metric thread
- UNF – Unified National Fine Thread
*Compared to standard threads (coarse thread), fine thread has a smaller pitch.
Unified threads come in three different classes:
1A (external) & 1B (internal): for applications where a liberal tolerance is required to permit easy assembly even with slightly nicked threads.
2A (external) & 2B (internal): most commonly used class for general applications.
3A (external) & 3B (internal): for applications where closeness of fit and/or accuracy of thread elements are important.
If you have any questions please contact us or check out our fittings with UNF thread.
Flank angle is 60 °.
Female and male thread are both parallel.
UNC (2A)
| Nominal diameter | Major diameter (mm) | Minor diameter (mm) | TPI |
| 1/4" x 20 UNC | 6,322 | 4,978 | 20 |
| 5/16" x 18 UNC | 7,907 | 6,401 | 18 |
| 3/8" x 16 UNC | 9,491 | 7,798 | 16 |
| 7/16" x 14 UNC | 11,076 | 9,144 | 14 |
| 1/2" x 13 UNC | 12,661 | 10,592 | 13 |
| 5/8" x 11 UNC | 15,834 | 13,386 | 11 |
| 3/4" x 10 UNC | 19,004 | 16,307 | 10 |
| 7/8" x 9 UNC | 22,176 | 19,177 | 9 |
| 1" x 8 UNC | 25,349 | 21,971 | 8 |
| 2" x 4,5 UNC | 50,726 | 44,679 | 4.5 |
UNF (2A)
| Nominal diameter | Major diameter (mm) | Minor diameter (mm) | TPI |
| 1/4" x 28 UNF | 6,325 | 5,360 | 28 |
| 5/16" x 24 UNF | 7,910 | 6,782 | 24 |
| 3/8" x 24 UNF | 9,497 | 8,382 | 24 |
| 7/16" x 20 UNF | 11,079 | 9,728 | 20 |
| 1/2" x 20 UNF | 12,667 | 11,328 | 20 |
| 5/8" x 18 UNF | 15,839 | 14,351 | 18 |
| 3/4" x 16 UNF | 19,012 | 17,323 | 16 |
| 7/8" x 14 UNF | 22,184 | 20,269 | 14 |
| 1" x 12 UNF | 25,354 | 23,114 | 12 |
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