This Standard specifies the thread form, series, class, allowance, tolerance, and designation for unified screw threads. (In order to emphasize that unified screw threads are based on inch modules, they may be denoted unified inch screw threads.) Several variations in thread form have been developed for unified threads; however, this Standard covers only UN, UNR, and UNJ thread forms.
The UNR thread form and UN thread form are identical except that the roots of the external threads are rounded with a radius of curvature between 0.108 and 0.144 times the pitch. The rounded root improves fatigue strength compared to the UN thread form.
The UNR thread designation standard was developed during the 1950s due to the request for fatigue-resistant safety- critical fasteners. Almost all externally threaded
fastener manufacturers produce UNR rolled threads rather than plain unified form threads.
• UNC – Unified National Coarse Thread - comparable with the ISO metric thread
• UNF – Unified National Fine Thread
• Female and Male UNC/UNF threads are both parallel
• The UNC/UNF flank angle is 60°
Unified threads comes in three different classes:
a ) for applications where a liberal tolerance is required to permit easy assembly even withslightly
nicked threads
b ) most commonly used class for general applications
c ) for applications where closeness of fit and/or accuracy of
thread elements are important
UNC threads according ANSI B1.1:
|
Major Diameter |
Threads per inch |
Major Diameter |
Tap Drill Size |
Pitch |
|
|
(in) |
(tpi) |
(in) |
(mm) |
(mm) |
(mm) |
|
#1 - 64 |
64 |
0.073 |
1.854 |
1.5 |
0.397 |
|
#2 - 56 |
56 |
0.086 |
2.184 |
1.8 |
0.453 |
|
#3 - 48 |
48 |
0.099 |
2.515 |
2.1 |
0.529 |
|
#4 - 40 |
40 |
0.112 |
2.845 |
2.35 |
0.635 |
|
#5 - 40 |
40 |
0.125 |
3.175 |
2.65 |
0.635 |
|
#6 - 32 |
32 |
0.138 |
3.505 |
2.85 |
0.794 |
|
#8 - 32 |
32 |
0.164 |
4.166 |
3.5 |
0.794 |
|
#10 - 24 |
24 |
0.19 |
4.826 |
4 |
1.058 |
|
#12 - 24 |
24 |
0.216 |
5.486 |
4.65 |
1.058 |
|
1/4" - 20 |
20 |
0.25 |
6.35 |
5.35 |
1.27 |
|
5/16" - 18 |
18 |
0.313 |
7.938 |
6.8 |
1.411 |
|
3/8" - 16 |
16 |
0.375 |
9.525 |
8.25 |
1.587 |
|
7/16" - 14 |
14 |
0.438 |
11.112 |
9.65 |
1.814 |
|
1/2" - 13 |
13 |
0.5 |
12.7 |
11.15 |
1.954 |
|
9/16" - 12 |
12 |
0.563 |
14.288 |
12.6 |
2.117 |
|
5/8" - 11 |
11 |
0.625 |
15.875 |
14.05 |
2.309 |
|
3/4" - 10 |
10 |
0.75 |
19.05 |
17 |
2.54 |
|
7/8" - 9 |
9 |
0.875 |
22.225 |
20 |
2.822 |
|
1" - 8 |
8 |
1 |
25.4 |
22.85 |
3.175 |
|
1 1/8" - 7 |
7 |
1.125 |
28.575 |
25.65 |
3.628 |
|
1 1/4" - 7 |
7 |
1.25 |
31.75 |
28.85 |
3.628 |
|
1 3/8" - 6 |
6 |
1.375 |
34.925 |
31.55 |
4.233 |
|
1 1/2" - 6 |
6 |
1.5 |
38.1 |
34.7 |
4.233 |
|
1 3/4" - 5 |
5 |
1.75 |
44.45 |
40.4 |
5.08 |
|
2" - 4 1/2 |
4 1/2 |
2 |
50.8 |
46.3 |
5.644 |
|
2 1/4" - 4 1/2 |
4 1/2 |
2.25 |
57.15 |
52.65 |
5.644 |
|
2 1/2" - 4 |
4 |
2.5 |
63.5 |
58.5 |
6.35 |
|
2 3/4" - 4 |
4 |
2.75 |
69.85 |
64.75 |
6.35 |
|
3" - 4 |
4 |
3 |
76.2 |
71.1 |
6.35 |
|
3 1/4" - 4 |
4 |
3.25 |
82.55 |
77.45 |
6.35 |
|
3 1/2" - 4 |
4 |
3.5 |
88.9 |
83.8 |
6.35 |
|
3 3/4" - 4 |
4 |
3.75 |
95.25 |
90.15 |
6.35 |
|
4" - 4 |
4 |
4 |
101.6 |
96.5 |
6.35 |
Example - Typical designation of an UNC thread
• 1/4” x 20 UNC
UNF threads ANSI B1.1:
|
Major Diameter |
Threads per inch |
Major Diameter |
Tap Drill Size |
Pitch |
|
|
(in) |
(tpi) |
(in) |
(mm) |
(mm) |
(mm) |
|
#0 - 80 |
80 |
0.06 |
1.524 |
1.25 |
0.317 |
|
#1 - 72 |
72 |
0.073 |
1.854 |
1.55 |
0.353 |
|
#2 - 64 |
64 |
0.086 |
2.184 |
1.9 |
0.397 |
|
#3 - 56 |
56 |
0.099 |
2.515 |
2.15 |
0.453 |
|
#4 - 48 |
48 |
0.112 |
2.845 |
2.4 |
0.529 |
|
#5 - 44 |
44 |
0.125 |
3.175 |
2.7 |
0.577 |
|
#6 - 40 |
40 |
0.138 |
3.505 |
2.95 |
0.635 |
|
#8 - 36 |
36 |
0.164 |
4.166 |
3.5 |
0.705 |
|
#10 - 32 |
32 |
0.19 |
4.826 |
4.1 |
0.794 |
|
#12 - 28 |
28 |
0.216 |
5.486 |
4.7 |
0.907 |
|
1/4" - 28 |
28 |
0.25 |
6.35 |
5.5 |
0.907 |
|
5/16" - 24 |
24 |
0.313 |
7.938 |
6.9 |
1.058 |
|
3/8" - 24 |
24 |
0.375 |
9.525 |
8.5 |
1.058 |
|
7/16" - 20 |
20 |
0.438 |
11.112 |
9.9 |
1.27 |
|
1/2" - 20 |
20 |
0.5 |
12.7 |
11.5 |
1.27 |
|
9/16" - 18 |
18 |
0.563 |
14.288 |
12.9 |
1.411 |
|
5/8" - 18 |
18 |
0.625 |
15.875 |
14.5 |
1.411 |
|
3/4" - 16 |
16 |
0.75 |
19.05 |
17.5 |
1.587 |
|
7/8" - 14 |
14 |
0.875 |
22.225 |
20.4 |
1.814 |
|
1" - 12 |
12 |
1 |
25.4 |
23.25 |
2.117 |
|
1 1/8" - 12 |
12 |
1.125 |
28.575 |
26.5 |
2.117 |
|
1 1/4" - 12 |
12 |
1.25 |
31.75 |
29.5 |
2.117 |
|
1 3/8" - 12 |
12 |
1.375 |
34.925 |
32.75 |
2.117 |
|
1 1/2" - 12 |
12 |
1.5 |
38.1 |
36 |
2.117 |
Example - Typical designation of an UNF thread
• 1/2” x 20 UNF
