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Straight
UNF
Unified National Fine
The fine-pitch Unified series, the thread most straight O-ring boss (ORB) hydraulic ports are cut to. The finer pitch gives a shallower, higher-precision engagement than UNC at the same nominal size.
- Standard
- ASME B1.1
- Flank angle
- 60° included
- Sealing
- None inherent -- an O-ring boss (SAE J1926 / ORB) seals on a separate elastomer, not the thread.
Thread profile
A 60° included flank angle with a flat-truncated crest and root -- the single fastest way to tell a Unified/American pipe thread from the other family by eye.
Cut straight: the pitch diameter is constant along the full thread length, with no taper.
Size chart
| Nominal | TPI | Pitch | Major Ø | Pitch Ø | Minor Ø | Tap drill |
|---|---|---|---|---|---|---|
| #4 | 48 | 0.0208" | 0.1120" | 0.0985" | 0.0849" | #42 (0.0917") |
| #6 | 40 | 0.0250" | 0.1380" | 0.1218" | 0.1055" | #33 (0.1136") |
| #8 | 36 | 0.0278" | 0.1640" | 0.1460" | 0.1279" | #29 (0.1369") |
| #10 | 32 | 0.0313" | 0.1900" | 0.1697" | 0.1494" | #21 (0.1596") |
| 1/4 | 28 | 0.0357" | 0.2500" | 0.2268" | 0.2036" | #3 (0.2152") |
| 5/16 | 24 | 0.0417" | 0.3125" | 0.2854" | 0.2584" | I (0.2719") |
| 3/8 | 24 | 0.0417" | 0.3750" | 0.3479" | 0.3209" | Q (0.3344") |
| 7/16 | 20 | 0.0500" | 0.4375" | 0.4050" | 0.3725" | 25/64" (0.3888") |
| 1/2 | 20 | 0.0500" | 0.5000" | 0.4675" | 0.4350" | 29/64" (0.4513") |
| 5/8 | 18 | 0.0556" | 0.6250" | 0.5889" | 0.5528" | 37/64" (0.5709") |
| 3/4 | 16 | 0.0625" | 0.7500" | 0.7094" | 0.6688" | 11/16" (0.6891") |
| 7/8 | 14 | 0.0714" | 0.8750" | 0.8286" | 0.7822" | 13/16" (0.8054") |
| 1 | 12 | 0.0833" | 1.0000" | 0.9459" | 0.8917" | 59/64" (0.9188") |
Tap drill calculator
Calculated live
Tap drill#420.0917" calculated · #42 (0.0917") nearest standard
- Pitch
- 0.0208"
- Pitch diameter (basic)
- 0.0985"
- Minor diameter (basic)
- 0.0849"
- Clearance drill (normal)
- #27 (0.1432")
Comparing against another standard? Open the universal calculator →