公稱尺寸和
螺紋系大徑極限最小
最大中徑極限最小
最大每英吋牙數列代號
小徑max
螺胚直徑最小
最大8-32
(0.164-32)
0.15710.16310.13990.14280.12483.99034.14273.55353.62713.1699
3.583.614.074.104.724.755.455.486.946.988.408.449.839.87
10-24
(0.190-24)
0.18180.18900.15860.16190.13794.61774.80064.02844.11233.5027
12-24
(0.216-24)
0.20780.21500.18450.18790.16395.27815.46104.68634.77274.1631
1/4-20
(0.250-20)
0.24080.24890.21270.21640.18766.11636.32215.40265.49664.7650
5/16-18
(0.3175-18)
0.30260.31130.27120.27520.24317.68607.90706.88856.99016.1747
3/8-16
(0.375-16)
0.36430.37370.32870.33310.29709.25329.49208.34908.46077.5438
unc7/16-14
(0.4375-14)
0.42580.43610.38500.38970.348510.815311.07699.77909.89848.8519
1/2-13
(0.50-13)
11.34 11.38
12.385012.661911.264911.391910.2641
12.80 12.84
13.957314.246912.740612.872711.6510
14.27 14.32
15.527015.834414.196114.335813.0023
17.28 17.33
18.676619.004317.203417.353315.8877
20.27 20.32
21.823722.176720.182820.342918.7147
23.22 23.27
24.968225.349223.114023.286721.4528
0.48760.49850.
44350.44850.40410.
54950.56090.50160.
50680.45870.61130.
62340.55890.56440.
51190.73530.74820.
67730.68320.62550.
85920.87310.79460.
80090.73680.98300.
99800.91000.91680.
8446
9/16-12
(0.5625-12)
5/8-11
(0.625-11)
3/4-10
(0.750-10)
7/8-9
(0.875-9)
1"-8
(1.000-8)
1.螺胚直徑指滾絲前的尺寸，數值為依經驗公式計算而得，在實踐中需驗證。2.
標記示例：10-24unc-2a(或0.190-24unc-2a)、3/8-16unc-2a(或0.
375-16unc-2a)（注：表中上行斜體數值單位為英吋，下行為公釐）
1公稱尺寸和
美制外螺紋（2a）常用規格極限尺寸表（細牙）
螺紋系大徑極限最小
最大中徑極限最小
最大每英吋牙數列代號
小徑max
螺胚直徑最小
最大8-36
(0.164-36)
0.15770.16320.14240.14520.12914.00564.14533.61703.68813.2791
3.653.674.244.274.824.855.695.717.177.208.758.78
10-32
(0.190-32)
0.18310.18910.16580.16880.15084.65074.80314.21134.28753.8303
12-28
(0.216-28)
0.20850.21500.18860.19180.17125.29595.46104.79044.87174.3485
1/4-28
(0.250-28)
0.24250.24900.22250.22580.20526.15956.32465.65155.73535.2121
5/16-24
(0.3175-24)
0.30420.31140.28060.28430.26037.72677.90967.12727.22126.6116
3/8-24
(0.375-24)
0.36670.37390.34300.34680.32289.31429.49718.71228.80878.1991
unf7/16-20
(0.4375-20)
10.19 10.23
10.873711.079510.147310.25409.5225
11.78 11.82
12.461212.667011.732311.841511.1100
13.27 13.31
14.031014.251913.220713.335012.5197
14.85 14.89
15.618515.839414.803114.922514.1072
17.91 17.95
18.773119.011917.853717.980717.0637
20.93 20.97
21.922722.184420.868621.005819.9593
23.90 23.95
25.064725.354323.830323.980122.7584
0.42810.43620.
39950.40370.37490.
49060.49870.46190.
46620.43740.55240.
56110.52050.52500.
49290.61490.62360.
58280.58750.55540.
73910.74850.70290.
70790.67180.86310.
87340.82160.82700.
78580.98680.99820.
93820.94410.8960
1/2-20
(0.50-20)
9/16-18
(0.5625-18)
5/8-18
(0.625-18)
3/4-16
(0.750-16)
7/8-14
(0.875-14)
1"-12
(1.000-12)
1.螺胚直徑指滾絲前的尺寸，數值為依經驗公式計算而得，在實踐中需驗證。2.
標記示例：10-32unf-2a(或0.190-32unf-2a)、3/8-24unf-2a(或0.
375-24unf-2a)
2公稱尺寸和
美制內螺紋（2b）常用規格極限尺寸表（粗牙）
螺紋系小徑極限最小
最大中徑極限最小
最大每英吋牙數列代號
大徑min
底孔直徑最小
最大8-32
(0.164-32)
0.13000.13900.14370.14750.16403.30203.53063.65003.74654.1656
3.403.503.753.904.404.555.055.206.456.607.858.009.209.40
10-24
(0.190-24)
0.14500.15600.16290.16720.19003.68303.96244.13774.24694.8260
12-24
(0.216-24)
0.17100.18100.18890.19330.21604.34344.59744.79814.90985.4864
1/4-20
(0.250-20)
0.19600.20700.21750.22240.25004.97845.25785.52455.64906.3500
5/16-18
(0.3175-18)
0.25200.26500.27640.28170.31256.40086.73107.02067.15527.9375
3/8-16
(0.375-16)
0.30700.32100.33440.34010.37507.79788.15348.49388.63859.5250
unc7/16-14
(0.4375-14)
0.36000.37600.39110.39720.43759.14409.55049.933910.088911.1125
1/2-13
(0.50-13)
10.65 10.90
10.591811.023611.430011.595112.7000
12.05 12.30
11.988812.446012.913413.086114.2875
13.45 13.70
13.385813.868414.376414.559315.8750
16.40 16.70
16.306816.840217.399017.594619.0500
19.30 19.60
19.177019.761220.391120.599422.2250
22.10 22.40
21.971022.606023.337523.561025.4000
0.41700.43400.
45000.45650.50000.
47200.49000.50840.
51520.56250.52700.
54600.56600.57320.
62500.64200.66300.
68500.69270.75000.
75500.77800.80280.
81100.87500.86500.
89000.91880.92761.
0000
9/16-12
(0.5625-12)
5/8-11
(0.625-11)
3/4-10
(0.750-10)
7/8-9
(0.875-9)
1"-8
(1.000-8)
1.底孔直徑指攻絲前鑽孔直徑，鑄鐵、黃銅等較軟料取小值，鋼、青銅等較硬料取大值。2.
標記示例：10-24unc-2b(或0.190-24unc-2b)、3/8-16unc-2b(或0.
375-16unc-2b)
3公稱尺寸和
美制內螺紋（2b）常用規格極限尺寸表（細牙）
螺紋系小徑極限最小
最大中徑極限最小
最大每英吋牙數列代號
大徑min
底孔直徑最小
最大8-36
(0.164-36)
0.13400.14200.14600.14960.16403.40363.60683.70843.79984.1656
3.453.674.004.274.554.855.405.716.857.208.458.789.8510.23
10-32
(0.190-32)
0.15600.16400.16970.17360.19003.96244.16564.31044.40944.8260
12-28
(0.216-28)
0.17700.18600.19280.19700.21604.49584.72444.89715.00385.4864
1/4-28
(0.250-28)
0.21100.22000.22680.23110.25005.35945.58805.76075.86996.3500
5/16-24
(0.3175-24)
0.26700.27700.28540.29020.31256.78187.03587.24927.37117.9375
3/8-24
(0.375-24)
0.33000.34000.34790.35280.37508.38208.63608.83678.96119.5250
unf7/16-20
(0.4375-20)
0.38300.39500.40500.41040.43759.728210.033010.287010.424211.1125
1/2-20
(0.50-20)
11.40 11.82
11.328411.607811.874512.016712.7000
12.85 13.31
12.750813.081013.370613.520414.2875
14.45 14.89
14.351014.681214.958115.110515.8750
17.40 17.95
17.322817.678418.018818.183919.0500
20.35 20.97
20.269220.675621.046421.224222.2250
23.90 23.95
23.114023.571224.025924.218925.4000
0.44600.45700.
46750.47310.50000.
50200.51500.52640.
53230.56250.56500.
57800.58890.59490.
62500.68200.69600.
70940.71590.75000.
79800.81400.82860.
83560.87500.91000.
92800.94590.95351.
0000
9/16-18
(0.5625-18)
5/8-18
(0.625-18)
3/4-16
(0.750-16)
7/8-14
(0.875-14)
1"-12
(1.000-12)
1.底孔直徑指攻絲前鑽孔直徑，鑄鐵、黃銅等較軟料取小值，鋼、青銅等較硬料取大值。2.
標記示例：10-32unf-2b(或0.190-32unf-2b)、3/8-24unf-2b(或0.
375-24unf-2b)4
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