UNC, UNF, UNEF, UNS
screw thread gauges to 1 inch in diameter

Share this page

Using a mobile device? More readable, less info, pages are here: UNC UNF

Index to fastener thread series

Content

Table

History

Nomenclature

These series (and the UNR, UNJ and fixed-pitch series) are the inch-based thread series currently used in the United States, and have been since 1949.¹ They superceded the American National Series (NC, NF, etc.)

Pink shading indicates secondary sizes whose use is discouraged by standards organizations.

See this table for diameters of twist drills.

The tap drill sizes are listed in the order in which the threads per inch (tpi) are listed in the previous column.

Gage
and
Fractional
Sizes
Major diam.
(inches)
Clear-
ance
drill
UNC
tpi
Tap drill
for UNC
UNF
tpi
Tap drill
for UNF
UNEF
tpi
UNS
tpi
Tap drill
for UNS
Nut Size
0 0.0600 #52 80 ³⁄₆₄″  — ⁵⁄₃₂″
1 0.0730 #48 64 #53 72 #53 #54 ⁵⁄₃₂″
2 0.0860 #43 56 #50 64 #50 ³⁄₁₆″
3 0.0990 #37 48 #47 56 #45 ³⁄₁₆″
4 0.1120 #32 40 #43 48 #42 32,
36
#45,
#44
¼″
5 0.1250 #30 40 #38 44 #37 36 #40 ¼″
6 0.1380 #27 32 #36 40 #33 36 #34 ⁵⁄₁₆″
8 0.1640 #18 32 #29 36 #29 30,
40
#30,
#28
¹¹⁄₃₂″
10 0.190 #9 24 #26 32 #21   28,
36,
40,
48,
56,
30
#23,
#22
³⁄₈″
12 0.216 #2 24 #16 28   32 36,
40,
48,
56
#13 ⁷⁄₁₆″
¼″ 0.2500 F 20 #7 28 #3 32 24,
27,
32,
36,
40,
48,
56
4,
3,
⁷⁄₃₂″
⁷⁄₁₆″
⁵⁄₁₆″ 0.3125 P 18 F 24 I 32 20,
27,
28,
36,
40
48
¹⁷⁄₆₄″,
J,
⁹⁄₃₂
⁹⁄₁₆″
³⁄₈″ 0.375 W 16 ⁵⁄₁₆″ 24 Q 32 18,
27,
36,
40
  ⁵⁄₈″
0.390 0.390 ²⁵⁄₆₄ 27    
⁷⁄₁₆″ 0.4375 29⁄₆₄″ 14 U 20 ²⁵⁄₆₄″ 28 18,
24,
27
   
½″ 0.5000  ³³⁄₆₄″ 13
(see
note
2
)
²⁷⁄₆₄″ 20 ²⁹⁄₆₄″ 28 12,
14,
18,
24,
27
  ¾″
⁹⁄₁₆″ 0.5625 ⁹⁄₁₆″ 12 ³¹⁄₆₄″ 18 ³³⁄₆₄″ 24 14,
27
   
⁵⁄₈″ 0.6250 ⁵⁄₈″ 11 ¹⁷⁄₃₂″ 18 ³⁷⁄₆₄″ 24 14,
27
   
¹¹⁄₁₆″  0.68753 ¹¹⁄₁₆         24    
¾″ 0.7500 ¾ 10 ²¹⁄₃₂″ 16   20 14,
18,
24
  1¹⁄₈″
¹³⁄₁₆″ 0.8125 ¹³⁄₁₆″ 20    
⁷⁄₈″ 0.8750 ⁷⁄₈″ 9 ⁴⁹⁄₆₄″ 14   20 10,
18,
24,
27
  1⁵⁄₁₆″
¹⁵⁄₁₆″ 0.9375 ¹⁵⁄₁₆″ 20    
1″ 1.0000 1″ 8 ⁷⁄₈″ 12   20 10,
14,
18,
24,
27
  1½″

History

The differences between American and British thread forms became a painful problem during the Second World War, especially in manufacturing and repairing airplane engines. In 1948 representatives of Britain, Canada and the United States agreed on a Unified Standard.

drawing of unified screw thread form

In the compromise the British accepted the 60° thread angle, and the Americans accepted rounded roots and optionally rounded crests. Five classes of fit were defined. The new fasteners continued to fit, for most practical purposes, ones manufactured under the old American National Standards. NC became UNC, NF became UNF, etc.

The UNS series is a catch-all category for threads which have the American Standard form, but whose pitches are not in the Unified Coarse (UNC) or Unified Fine (UNF) series.

Nomenclature

1. B1.1-1949

2. In the Unified National Series the ½ inch size has 13 threads per inch, but the American Standard was 12 threads per inch.

standards

British Standard 1580 Unified (ISO, inch) screw threads: Parts 1 and 2 (1962); Part 3 (1965).

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