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Index to fastener thread series
The Unified National Fine series are the inch-based thread series currently used in the United States, and have been since 1949.¹ They superseded the American National Series (NF).
Pink shading = obsolete sizes that might be found on old equipment but aren't used on new.
Nut size is the distance across flats.
See this table for diameters of twist drills.
| Gage and frac- tional sizes |
Major diam. (inches) |
Clear- ance drill |
tpi | Tap drill |
Nut size |
|---|---|---|---|---|---|
| 0 | 0.0600 | #52 | 80 | ³⁄64″ | 5⁄₃₂″ |
| 1 | 0.0730 | #48 | 72 | #53 | ⁵⁄₃₂″ |
| 2 | 0.0860 | #43 | 64 | #50 | ³⁄₁₆″ |
| 3 | 0.0990 | #37 | 56 | #45 | ³⁄₁₆″ |
| 4 | 0.1120 | #32 | 48 | #42 | ¼″ |
| 5 | 0.1250 | #30 | 44 | #37 | ¼″ |
| 6 | 0.1380 | #27 | 40 | #33 | ⁵⁄₁₆″ |
| 8 | 0.1640 | #18 | 36 | #29 | ¹¹⁄₃₂″ |
| 10 | 0.190 | #9 | 32 | #21 | ³⁄₈″ |
| 12 | 0.216 | #2 | 28 | ⁷⁄₁₆″ | |
| ¼″ | 0.2500 | F | 28 | #3 | ⁷⁄₁₆″ |
| ⁵⁄₁₆″ | 0.3125 | P | 24 | I | 9⁄₁₆″ |
| ³⁄₈″ | 0.375 | W | 24 | Q | ⁵⁄₈″ |
| 0.390 | 0.390 | ²⁵/₆₄ | — | — | |
| 7⁄₁₆″ | 0.4375 | ²⁹⁄₆₄″ | 20 | ²⁵⁄₆₄″ | |
| ½″ | 0.5000 | ³³/₆₄″ | 20 | 29⁄₆₄″ | ¾″ |
| ⁹⁄₁₆″ | 0.5625 | ⁹⁄₁₆″ | 18 | 33⁄₆₄″ | |
| 5⁄₈″ | 0.6250 | 5⁄₈″ | 18 | 37⁄₆₄″ | |
| ¾″ | 0.7500 | ¾ | 16 | 1¹⁄₈″ | |
| 7⁄₈″ | 0.8750 | 7⁄₈″ | 14 | 15⁄16″ | |
| 1″ | 1.0000 | 1″ | 12 | 1½″ |
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Copyright © 2000 Sizes, Inc. All rights reserved.
Last revised: 9 December 2005.