美制统一螺纹（UN)钢丝螺套，也叫美制螺纹钢丝螺套、统一螺纹钢丝螺套、英寸制螺纹钢丝螺套，安装完成后形成标准的美制螺纹（也叫统一螺纹、英寸制螺纹），精度为2B，高时达到3B。螺纹代号为UN（粗牙为UNC、细牙为UNF、超细牙为UNEF)。
标记方法：
美制统一螺纹钢丝螺套的标记由钢丝螺套型号代号（如FR）、公称直径、牙数、螺纹代号（如UNC）、公称长度组成。
如，普通型钢丝螺套，公称直径为1/4英寸、每英寸牙数为20牙、公称长度为1.5d的粗牙美制统一螺纹标记为：
FR 1/4″-20UNC-1.5d
再如，公称直径为1/4英寸、每英寸牙数为28牙、公称长度为1.5d的自锁型细牙美制统一螺纹钢丝螺标记为：
SL 1/4″-28UNF-1.5d
标记说明：
1、 钢丝螺套的公称直径是指钢丝螺套安装完成后形成的内螺纹的直径（或与其相配合的螺栓直径），单位为英寸，即“″。小规格螺套用代号表示，如NO.8-32（此中的“8”为公称直径代号，对应的英寸数为0.164英寸）。实际运用中，人们往往将英寸中的“″”略去，也将代号中的“NO.”略去，直接写成FR 1/4-28UNF-1.5d、FR 8-32UNC-1.5d。
2、长度除了用系数和公称直径表示外，也有直接用安装钢丝螺套的螺纹孔深的毫米数或英寸数表示的，如，FR 1/4″-20UNC-0.375″或FR 1/4″-20UNC-9.525mm。值得注意的是这里的“″”和“mm”也有人略去不写，这就要根据实际情况具体对待了。
UNC UNF统一螺纹螺纹护套规格参数表
|
直径号-牙数
|
直径
|
螺距
|
k×d
|
安装后长度L(mm)
|
安装前圈数N(≈)
|
安装前外径(mm)
|
钻头直径do(mm)
|
|
2-56
|
2.184
|
1d
|
2.18
|
3.3
|
2.7-3.1
|
2.3
|
|
0.454
|
1.5d
|
3.28
|
5
|
|
2d
|
4.37
|
6.8
|
|
4-40
|
2.845
|
1d
|
2.9
|
3.2
|
3.6-4.0
|
3.0
|
|
0.635
|
1.5d
|
4.3
|
5.1
|
|
2d
|
5.8
|
7.2
|
|
5-40
|
3.175
|
1d
|
3.2
|
3.7
|
4.0-4.4
|
3.3
|
|
0.635
|
1.5d
|
4.8
|
5.9
|
|
2d
|
6.4
|
8.2
|
|
6-32
|
3.505
|
1d
|
3.5
|
2.8
|
4.5-4.9
|
3.7
|
|
0.794
|
1.5d
|
5.3
|
4.8
|
|
2d
|
7
|
6.8
|
|
8-32
|
4.166
|
1d
|
4.2
|
4
|
5.2-5.6
|
4.4
|
|
0.794
|
1.5d
|
6.25
|
6
|
|
2d
|
8.3
|
8.7
|
|
8-36
|
4.166
|
1d
|
4.2
|
4.5
|
5.1-5.6
|
4.3
|
|
0.706
|
1.5d
|
6.3
|
7.2
|
|
2d
|
8.3
|
9.7
|
|
10-24
|
4.826
|
1d
|
4.8
|
3.3
|
6.1-6.6
|
5.1
|
|
1.058
|
1.5d
|
7.2
|
5.4
|
|
2d
|
9.6
|
7.5
|
|
10-32
|
4.826
|
1d
|
4.83
|
4.3
|
5.9-6.5
|
5.0
|
|
0.794
|
1.5d
|
7.24
|
6.9
|
|
2d
|
9.6
|
9.5
|
|
12-24
|
5.486
|
1d
|
5.5
|
4
|
6.8-7.2
|
5.8
|
|
1.058
|
1.5d
|
8.2
|
6.3
|
|
2d
|
11
|
8.8
|
|
1/4"-20
|
6.35
|
1d
|
6.4
|
3.9
|
7.8-8.3
|
6.7
|
|
1.27
|
1.5d
|
9.5
|
6.2
|
|
2d
|
12.7
|
8.6
|
|
1/4"-28
|
6.35
|
1d
|
6.35
|
5.3
|
7.7-8.3
|
6.6
|
|
0.907
|
1.5d
|
9.5
|
8.6
|
|
2d
|
12.7
|
11.8
|
|
5/16"-18
|
7.938
|
1d
|
7.9
|
4.3
|
9.6-10.2
|
8.3
|
|
1.411
|
1.5d
|
11.9
|
6.8
|
|
2d
|
15.9
|
9.4
|
|
5/16"-24
|
7.938
|
1d
|
7.9
|
5.9
|
9.6-10.2
|
8.2
|
|
1.058
|
1.5d
|
11.9
|
9.4
|
|
2d
|
15.9
|
12.8
|
|
3/8"-16
|
9.525
|
1d
|
9.5
|
4.8
|
11.4-11.9
|
9.9
|
|
1.588
|
1.5d
|
14.3
|
7.7
|
|
2d
|
19.1
|
10.6
|
|
3/8"-24
|
9.525
|
1d
|
9.5
|
7.3
|
11.4-11.9
|
9.8
|
|
1.058
|
1.5d
|
14.3
|
11.5
|
|
2d
|
19.1
|
15.6
|
|
7/16"-14
|
11.113
|
1d
|
11.1
|
4.9
|
13.3-13.9
|
11.6
|
|
1.814
|
1.5d
|
16.7
|
7.9
|
|
2d
|
22.2
|
10.7
|
|
7/16"-20
|
11.113
|
1d
|
11.1
|
7
|
13.3-13.7
|
11.4
|
|
1.27
|
1.5d
|
16.7
|
11.1
|
|
2d
|
22.2
|
15
|
|
1/2"-13
|
12.7
|
1d
|
12.7
|
5.2
|
15.1-15.7
|
13.2
|
|
1.954
|
1.5d
|
19.1
|
8.3
|
|
2d
|
25.4
|
11.4
|
|
1/2"-20
|
12.7
|
1d
|
12.7
|
7.9
|
15-15.6
|
13.0
|
|
1.27
|
1.5d
|
19.1
|
12.8
|
|
2d
|
25.4
|
17.3
|
|
9/16"-18
|
14.288
|
1d
|
14.3
|
7.9
|
16.91-17.55
|
14.6
|
|
1.411
|
1.5d
|
21.5
|
12
|
|
2d
|
28.6
|
16
|
|
5/8"-11
|
15.875
|
1d
|
15.9
|
5.7
|
18.8-19.4
|
16.5
|
|
2.309
|
1.5d
|
23.8
|
9
|
|
2d
|
31.8
|
12.3
|
|
5/8"-18
|
15.875
|
1d
|
15.9
|
9.4
|
18.6-19.3
|
16.2
|
|
1.411
|
1.5d
|
23.8
|
14.5
|
|
2d
|
31.8
|
19.7
|
|
3/4"-10
|
19.05
|
1d
|
19.1
|
6.3
|
22.3-23.0
|
19.7
|
|
2.54
|
1.5d
|
28.6
|
9.9
|
|
2d
|
38.1
|
13.5
|
|
3/4"-16
|
19.05
|
1d
|
19.1
|
10.1
|
22.2-22.8
|
19.4
|
|
1.588
|
1.5d
|
28.6
|
15.6
|
|
2d
|
31.8
|
21
|
|
7/8"-14
|
22.225
|
1d
|
22.2
|
10.3
|
25.9-26.7
|
22.6
|
|
1.814
|
1.5d
|
33.3
|
15.9
|
|
2d
|
44.5
|
21.6
|
|
1"-8
|
25.4
|
1d
|
25.4
|
6.8
|
29.6-30.4
|
26.1
|
|
3.175
|
1.5d
|
38.1
|
10.6
|
|
2d
|
50.8
|
15.4
|
|
1"-12
|
25.4
|
2.117
|
1d
|
25.4
|
10
|
29.6-30.4
|
30.0
|
|
1.5d
|
38.1
|
15.6
|
|
1"-14
|
25.4
|
1d
|
25.4
|
11.8
|
29.6-30.4
|
25.9
|
|
1.814
|
1.5d
|
38.1
|
18.1
|
|
2d
|
50.8
|
24.5
|
相关资料：公制螺纹护套
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