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Straight
UNC
Unified National Coarse
The standard coarse-pitch American fastener thread, common on flange bolting, clamps, and mounting hardware around piping systems.
- Standard
- ASME B1.1
- Flank angle
- 60° included
- Sealing
- None -- a fastening 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 | 40 | 0.0250" | 0.1120" | 0.0958" | 0.0795" | #43 (0.0876") |
| #6 | 32 | 0.0313" | 0.1380" | 0.1177" | 0.0974" | #36 (0.1076") |
| #8 | 32 | 0.0313" | 0.1640" | 0.1437" | 0.1234" | #29 (0.1336") |
| #10 | 24 | 0.0417" | 0.1900" | 0.1629" | 0.1359" | #25 (0.1494") |
| 1/4 | 20 | 0.0500" | 0.2500" | 0.2175" | 0.1850" | #7 (0.2013") |
| 5/16 | 18 | 0.0556" | 0.3125" | 0.2764" | 0.2403" | F (0.2584") |
| 3/8 | 16 | 0.0625" | 0.3750" | 0.3344" | 0.2938" | 5/16" (0.3141") |
| 7/16 | 14 | 0.0714" | 0.4375" | 0.3911" | 0.3447" | U (0.3679") |
| 1/2 | 13 | 0.0769" | 0.5000" | 0.4500" | 0.4001" | 27/64" (0.4251") |
| 5/8 | 11 | 0.0909" | 0.6250" | 0.5660" | 0.5069" | 17/32" (0.5364") |
| 3/4 | 10 | 0.1000" | 0.7500" | 0.6850" | 0.6201" | 21/32" (0.6526") |
| 7/8 | 9 | 0.1111" | 0.8750" | 0.8028" | 0.7307" | 49/64" (0.7667") |
| 1 | 8 | 0.1250" | 1.0000" | 0.9188" | 0.8376" | 7/8" (0.8782") |
Tap drill calculator
Calculated live
Tap drill#430.0876" calculated · #43 (0.0876") nearest standard
- Pitch
- 0.0250"
- Pitch diameter (basic)
- 0.0958"
- Minor diameter (basic)
- 0.0795"
- Clearance drill (normal)
- #27 (0.1432")
Comparing against another standard? Open the universal calculator →