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Index to fastener thread series
The Unified National Coarse series are now probably the most commonly-used inch-based thread series in the United States, and have been since 1949. They superseded the American National Series (NC).
Pink shading = obsolete sizes that might be found on old equipment but are not used on new equipment.
The table includes sizes not made in all types of bolts.
Nut size is width across flats of a hex nut.
See this table for diameters of twist drills.
| Gage and frac- tional sizes |
Major diameter (inches) |
Clear- ance drill |
tpi | Tap drill |
Nut size |
|---|---|---|---|---|---|
| 1 | 0.0730 | #48 | 64 | #53 | ⁵⁄₃₂″ |
| 2 | 0.0860 | #43 | 56 | #50 | ³⁄₁₆″ |
| 3 | 0.0990 | #37 | 48 | #47 | ³⁄₁₆″ |
| 4 | 0.1120 | #32 | 40 | #43 | ¼″ |
| 5 | 0.1250 | #30 | 40 | #38 | ¼″ |
| 6 | 0.1380 | #27 | 32 | #36 | ⁵⁄₁₆″ |
| 8 | 0.1640 | #18 | 32 | #29 | ¹¹⁄₃₂″ |
| 10 | 0.1900 | #9 | 24 | #26 | ³⁄₈″ |
| 12 | 0.2160 | #2 | 24 | #16 | ⁷⁄₁₆″ |
| ¼″ | 0.2500 | F | 20 | #7 | ⁷⁄₁₆″ |
| ⁵⁄₁₆″ | 0.3125 | P | 18 | F | ⁹⁄₁₆″ |
| ³⁄₈″ | 0.3750 | W | 16 | ⁵⁄₁₆″ | ⁵⁄₈″ |
| ⁷⁄₁₆″ | 0.4375 | ²⁹⁄₆₄″ | 14 | U | ⁵⁄₈″ |
| ½″ | 0.5000 | ³³⁄₆₄″ | 13* |
²⁷⁄₆₄″ | ¾″ |
| ⁹⁄₁₆″ | 0.5625 | ⁹⁄₁₆″ | 12 | ³¹⁄₆₄″ | ¹³⁄₁₆″ |
| ⁵⁄₈″ | 0.6250 | ⁵⁄₈″ | 11 | ¹⁷⁄₃₂″ | ¹⁵⁄₁₆″ |
| ¾″ | 0.7500 | ¾″ | 10 | ²¹⁄₃₂″ | 1¹⁄₈″ |
| ⁷⁄₈″ | 0.8750 | ⁷⁄₈″ | 9 | ⁴⁹⁄₆₄″ | 1⁵⁄₁₆″ |
| 1″ | 1.0000 | 1″ | 8 | ⁷⁄₈″ | 1½″ |
* In the Unified National Series the ½ inch size has 13 threads per inch, but the American Standard was 12 threads per inch.
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Last revised: 11 June 2017.