UNC
screw threads to 1 inch in diameter

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 They superceded the American National Series (NC).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
Fractional
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.

home | tools index | search |  contact drawing of envelope |  contributors | 
help | privacy | terms of use