螺纹底孔直径
一、螺纹底孔直径计算式
螺纹底孔直径可参照表1、表2的公式计算，也可查表3至表11。
表1 加工米制普通螺纹底孔钻头直径D的计算公式 1
D = d – t
式中 d：螺纹的公称直径 t：螺距
适用范围
（1）螺距t<1；
（2）工件材料塑性较大；（3）孔扩张量适中。 （1）螺距t<1；
（2）工件材料塑性较小；（3）孔扩张量较小。
2
D = d – (1.04～1.08)t
表2 加工英制螺纹底孔钻头直径的计算公式
(mm)
螺纹公称直径 (英寸)
铸铁与青铜
钢与黄铜
D = 25.4·(d - 1/n) + 0.1D = 25.4·(d - 1/n) + 0.2
3/16 \"～5/8 \" D = 25.4·(d - 1/n)3/4 \"～1 1/2 \" D = 25.4·(d - 1/n)注：n—每英寸牙数
·2·
二、螺纹底孔直径表
表3 米制粗牙螺纹攻丝前用的钻头直径(mm)
螺 纹
小 直 径 级 别
公称直径 螺距1 1.2 1.6 2 2.5 3 4 5 6 8 10 12 14 16 18 20 22 24
0.25 0.25 0.35 0.4 0.45 0.5 0.7 0.8 1 1.25 1.5 1.75 2 2 2.5 2.5 2.5 3
5H max 0.7850.9851.3011.6572.1122.5713.3824.2945.0076.8598.61210.37112.13514.13515.64917.64919.64921.152
6H max
7H max
5H、6H、7H
min 0.729 0.929 1.221 1.561 2.013 2.459 3.242 4.134 4.917 6.647 8.376 10.106 11.835 13.835 15.294 17.294 19.294 20.754
钻头直径0.750.951.251.602.052.503.304.205.006.808.5010.212.014.015.517.519.521.0
1.3211.6792.1382.5993.4224.3345.1536.9128.67610.44112.21014.21015.74417.74419.74421.252
2.6393.4664.3845.2176.9828.75110.53112.31014.31015.85417.85419.85421.382
·3·
表4 米制细牙螺纹攻丝前用的钻头直径(mm)
螺 纹
小 直 径 级 别
公称直径 螺距 2.5 3 4 5 6 8 10 8 10 12 14 16 18 20 22 24 10 12 14 12 14 15 16 18 20 22
5H max 2.201
0.35
2.701 3.571
0.5
4.571 5.338
0.75 7.338
9.338 7.107 9.107 11.10713.10715.1071
17.10719.10721.10723.1078.859
1.25 10.859
12.85910.61212.61213.612
1.5 14.612
16.61218.61220.612
6H max 2.221 2.721 3.599 4.599 5.378 7.378 9.378 7.217 9.217 11.21713.21715.21717.21719.21721.21723.2178.912 10.91212.91210.67612.67613.67614.67616.67618.67620.676
7H max 3.639 4.639 5.424 7.424 9.424 7.217 9.217 11.21713.21715.21717.21719.21721.21723.2178.982 10.98212.98210.75112.75113.75114.75116.75118.75120.751
5H、6H、7H
min 2.121 2.621 3.459 4.459 5.188 7.188 9.188 6.917 8.917 10.917 12.917 14.917 16.917 18.917 20.917 22.917 8.647 10.647 12.647 10.376 12.376 13.376 14.376 16.376 18.376 20.376
钻头直径2.152.653.504.505.707.209.207.009.0011.013.015.017.019.021.023.08.8010.812.810.512.513.514.516.518.520.5
·4·
螺 纹
小 直 径 级 别
公称直径 螺距 24 25 18 20 22 24 25
5H max 22.61223.61216.13518.13520.13522.13523.135
6H max 22.67623.67616.21018.21020.21022.21023.210
7H max 22.75123.75116.31018.31020.31022.31023.310
5H、6H、7H
min 22.376 23.376 15.835 17.835 19.835 21.835 22.835
钻头直径22.523.516.018.020.022.023.0
1.5
2
表5 英国标准粗牙惠氏螺纹 Ｂ、Ｓ、Ｗ攻丝前用的钻头直径(mm)
公称直径 （英寸） 3/16 1/4 5/16 3/8 1/2 5/8 3/4 7/8 1 1 1/8 1 1/4 1 1/2 1 3/4 2
每英寸牙数
24 20 18 16 12 11 10 9 8 7 7 6 5 4 1/2
钻 头 直 径
铸铁、青铜、黄铜
3.8 5.1 6.6 8.0 10.6 13.6 16.6 19.6 22.3 25.0 28.2 34.0 39.5 45.3
钢、可锻铸铁
3.9 5.2 6.7 8.1 10.7 13.8 16.8 19.7 22.5 25.2 28.4 34.2 39.7 45.6
·5·
表6 英寸制统一粗牙螺纹UNC攻丝前用的钻头直径(mm)
螺 纹
公称直径 每英寸（英寸） 牙 数No.1 No.2 No.3 No.4 No.5 No.6 No.8 No.10 No.12 1/4 5/16 3/8 7/16 1/2 9/16 5/8 3/4 7/8 1 1 1/8 1 1/4 1 3/8 1 1/2 1 3/4 2
64 56 48 40 40 32 32 24 24 20 18 16 14 13 12 11 10 9 8 7 7 6 6 5 4 1/2
小 直 径 级 别
螺 距0.397 0.454 0.529 0.635 0.635 0.794 0.794 1.058 1.058 1.270 1.411 1.588 1.814 1.954 2.117 2.309 2.540 2.822 3.175 3.629 3.629 4.233 4.233 5.080 5.644
2B max 1.5821.8722.1462.3852.6972.8963.5313.9624.5975.2686.7848.1649.55011.01312.45613.86816.83319.74822.59825.34928.52431.12034.29539.81445.598
3B max 1.5821.8722.1462.3852.6972.8963.5283.9504.5905.2506.6808.0829.44110.88112.30113.69316.62419.52022.34425.08228.25830.85134.02639.56045.367
2B、3Bmin 1.4251.6941.9412.1562.4872.6423.3023.6834.3434.9766.4117.8059.14910.58411.99613.37616.29919.16921.96324.64827.82330.34333.51938.95144.689
钻头 直径 1.55 1.85 2.10 2.35 2.65 2.85 3.50 3.90 4.60 5.10 6.60 8.00 9.40 10.80 12.20 13.50 16.50 19.50 22.25 25.00 28.00 30.75 34.00 39.50 45.00
·6·
表7 英寸制统一细牙螺纹UNF攻丝前用的钻头直径(mm)
螺 纹
公称直径 每英寸（英寸） 牙 数No.0 No.1 No.2 No.3 No.4 No.5 No.6 No.8 No.10 No.12 1/4 5/16 3/8 7/16 1/2 9/16 5/8 3/4 7/8 1 1 1/8 1 1/4 1 3/8 1 1/2
80 72 64 56 48 44 40 36 32 28 28 24 24 20 20 18 18 16 14 12 12 12 12 12
小 直 径 级 别
螺 距0.318 0.353 0.397 0.454 0.529 0.577 0.635 0.706 0.794 0.907 0.907 1.058 1.058 1.270 1.270 1.411 1.411 1.588 1.814 2.117 2.117 2.117 2.117 2.117
2B max 1.3061.6131.9132.1972.4592.7413.0233.6074.1664.7245.5807.0388.62610.03011.61813.08414.67117.68920.66323.56926.74429.91933.09436.269
3B max 1.3061.6131.9132.1972.4592.7413.0123.5974.1684.7175.5636.9958.5659.94711.52412.96914.55417.54620.49323.36326.53829.71332.88836.063
2B、3Bmin 1.1811.4731.7552.0242.2712.5502.8193.4043.9624.4965.3676.7928.3799.73811.32612.76114.34817.33020.26223.10926.28429.45932.63435.809
钻头 直径 1.25 1.55 1.90 2.15 2.40 2.70 2.95 3.50 4.10 4.70 5.50 6.90 8.50 9.90 11.50 12.90 14.50 17.50 20.40 23.25 26.50 29.50 32.75 36.00
·7·
表8 GB7307-87、ISO228/1-1982非螺纹密封的管螺纹
攻丝前用的钻头直径(mm)
螺 纹
公称直径 （英寸） 1/8 1/4 3/8 1/2 5/8 3/4 7/8 1 1 1/4 1 1/2 1 3/4 2
每英寸 牙 数 28 19 19 14 14 14 14 11 11 11 11 11
螺 距 0.907 1.337 1.337 1.814 1.814 1.814 1.814 2.309 2.309 2.309 2.309 2.309
小 直 径 max 8.848 11.890 16.395 19.172 21.128 24.658 28.418 30.931 39.592 45.485 51.428 75.296
min 8.566 11.445 14.950 18.631 20.587 24.117 27.877 30.291 38.952 44.845 50.788 56.556
钻头 直径 8.80 11.80 15.25 19.00 21.00 24.50 28.25 30.75 39.50 45.00 51.00 57.00
·8·
表9 GB7306-87、ISO7/1-1982用螺纹密封的管螺纹
攻丝前用的钻头直径(mm)
螺 纹
公称直径 （英寸） 1/8 1/4 3/8 1/2 3/4 1 1 1/4 1 1/2 2
每英寸 牙 数 28 19 19 14 14 11 11 11 11
螺 距 0.907 1.337 1.337 1.814 1.814 2.309 2.309 2.309 2.309
小 直 径 max 8.637 11.549 15.054 18.773 24.259 30.471 39.132 45.025 56.836
min 8.495 11.341 14.846 18.489 23.975 30.111 38.772 44.665 56.476
钻头 直径 8.60 11.50 15.00 18.50 24.00 30.25 39.00 45.00 56.50
·9·
表10 美标(NPT、NPSC)管螺纹底孔推荐的麻花钻直径(英寸) 公称直径
1 1/16 1/8 1/4 3/8 1/2 3/4 1 1 1/4 1 1/2 2 2 1/2
21/64 27/64 9/16 11/16 57/64 1 1/2
锥 螺 纹
使用铰刀
2
*0.240 *0.328 *0.4227/16 *0.5629/16 *0.68845/64 *0.89129/32
不用铰刀
3
*0.2461/4 *0.33211/32 *0.4387/16 *0.56237/64 *0.70323/32 *0.90659/64
直管螺纹
4 *0.250*0.344*0.438*0.578*0.719*0.922
*1.1251 9/64 *1.1411 5/32 *1.156
1.500 1.750
1 15/321.469 1 31/641.484 1 1/2 1 23/321.719 1 47/641.734 1 3/4
2 3/16 2.188 2 13/642.203 2 7/32 2.219 2 19/322.594 2 5/8
2.625 2 21/322.656
注：*为美国标准麻花钻尺寸
·10·
表11 美标(NPTF、NPSI)干密封管螺纹底孔推荐的
麻花钻直径(英寸) 公称直径
1 1/16 1/8 1/4 3/8 1/2 3/4 1 1 1/4 1 1/2 2 2 1/2 3
21/64 27/64 9/16 11/16 57/64 1 1/8
锥 螺 纹
使用铰刀
2
*0.234 *0.328 *0.4227/16 *0.56227/64 *0.68845/64 *0.89159/64
不用铰刀
3
*0.2461/4
直管螺纹
4 *0.250
*0.339*11/32 *0.344*0.436 *0.57827/64 *0.70323/32
*0.444*0.578*0.719
*0.922*59/64 *0.922
*1.1251 5/32 *1.1561 5/32 *1.156
1.500
1 15/321.469 1 1/2
1 45/641.703 1 47/641.734 2 3/16 2.188 2 7/32 2.219 2 19/322.594 2 41/642.641 3 7/32 3.219 3 17/643.266
注：*为美国标准麻花钻尺寸
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