UNF
screw threads to 1 inch in diameter

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Fine series are the inch-based thread series currently used in the United States, and have been since 1949.¹ They superceded the American National Series (NF).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
Fractional
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   1516
1″ 1.0000 1″ 12   1½″

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