Unified National Extra Fine (UNEF) Thread Chart
Industry Standard: ASME B1.1
Unified National Extra Fine (UNEF) threads have a very fine pitch, even tighter than the UNF standard. UNEF threads are used in highly specialized applications like thin-walled tubes, couplings, optical instruments, and aerospace components where extremely fine adjustments or minimal thread depth are required.
| Size | Ø Major (in) | TPI | Ø Pitch (in) | Ø Minor (in) | Tap Drill (in) | Stress Area (in²) |
|---|---|---|---|---|---|---|
| #12-32 UNEF | 0.2160 | 32 | 0.1957 | 0.1822 | 0.1848 | 0.0270 |
| 1/4-32 UNEF | 0.2500 | 32 | 0.2297 | 0.2162 | 0.2188 | 0.0379 |
| 5/16-32 UNEF | 0.3125 | 32 | 0.2922 | 0.2787 | 0.2813 | 0.0625 |
| 3/8-32 UNEF | 0.3750 | 32 | 0.3547 | 0.3412 | 0.3438 | 0.0932 |
| 7/16-28 UNEF | 0.4375 | 28 | 0.4143 | 0.3988 | 0.4018 | 0.1274 |
| 1/2-28 UNEF | 0.5000 | 28 | 0.4768 | 0.4613 | 0.4643 | 0.1700 |
| 9/16-24 UNEF | 0.5625 | 24 | 0.5354 | 0.5174 | 0.5208 | 0.2139 |
| 5/8-24 UNEF | 0.6250 | 24 | 0.5979 | 0.5799 | 0.5833 | 0.2682 |
| 11/16-24 UNEF | 0.6875 | 24 | 0.6604 | 0.6424 | 0.6458 | 0.3287 |
| 3/4-20 UNEF | 0.7500 | 20 | 0.7175 | 0.6959 | 0.7000 | 0.3863 |
| 13/16-20 UNEF | 0.8125 | 20 | 0.7800 | 0.7584 | 0.7625 | 0.4582 |
| 7/8-20 UNEF | 0.8750 | 20 | 0.8425 | 0.8209 | 0.8250 | 0.5362 |
| 15/16-20 UNEF | 0.9375 | 20 | 0.9050 | 0.8834 | 0.8875 | 0.6204 |
| 1"-20 UNEF | 1.0000 | 20 | 0.9675 | 0.9459 | 0.9500 | 0.7107 |
| 1-1/16-18 UNEF | 1.0625 | 18 | 1.0264 | 1.0024 | 1.0069 | 0.7986 |
| 1-1/8-18 UNEF | 1.1250 | 18 | 1.0889 | 1.0649 | 1.0694 | 0.9007 |
| 1-3/16-18 UNEF | 1.1875 | 18 | 1.1514 | 1.1274 | 1.1319 | 1.0089 |
| 1-1/4-18 UNEF | 1.2500 | 18 | 1.2139 | 1.1899 | 1.1944 | 1.1232 |
| 1-5/16-18 UNEF | 1.3125 | 18 | 1.2764 | 1.2524 | 1.2569 | 1.2437 |
| 1-3/8-18 UNEF | 1.3750 | 18 | 1.3389 | 1.3149 | 1.3194 | 1.3703 |
| 1-7/16-18 UNEF | 1.4375 | 18 | 1.4014 | 1.3774 | 1.3819 | 1.5030 |
| 1-1/2-18 UNEF | 1.5000 | 18 | 1.4639 | 1.4399 | 1.4444 | 1.6419 |
| 1-5/8-18 UNEF | 1.6250 | 18 | 1.5889 | 1.5649 | 1.5694 | 1.9381 |
| 1-3/4-16 UNEF | 1.7500 | 16 | 1.7094 | 1.6823 | 1.6875 | 2.2408 |
| 2"-16 UNEF | 2.0000 | 16 | 1.9594 | 1.9323 | 1.9375 | 2.9532 |
Standard FAQs
When should UNEF threads be used?
UNEF threads are ideal for thin-walled parts where coarser threads would cut too deep, or in high-precision equipment where tiny adjustments in positioning are required.