普通螺纹钻底孔用钻头直径尺寸 计算公式：P>1mm时，D=d-P； P<1mm时，D=d-(1～1.1)P 式中：P—螺距（mm） D—攻螺纹前钻头直径（mm） d—螺纹公称直径（mm）螺 距螺 距公称直径钻头直径公称直径PPdDd粗0.250.75粗21细0.20.81.514细粗0.41.61.252细0.251.751粗0.52.5粗2316细0.352.651.5细粗0.73.314细0.53.5粗2.5粗0.84.22518细细0.54.51.5粗1516细0.755.2粗2.5粗1.256.72208细171.5细0.757.21粗1.58.5粗2.51.258.721022细细1910.50.759.21粗1.7510.2粗31.510.521224细细1.2510.71.51111螺 距螺 距公称直径钻头直径公称直径粗323.9粗4.5224.9427细421.525.53细1262粗3.526.31.5326.9粗4.530227.94细451.528.53细1292粗3.529.31.5329.9粗533细230.94481.531.53细粗431.82332.91.536细233.9粗51.534.5452粗434.83细335.9239细236.91.5钻头直径D11.912.512.71313.914.51515.415.916.51717.417.918.51919.419.920.52120.921.922.523钻头直径37.337.838.939.940.540.340.841.942.943.542.743.844.945.946.546.747.848.949.950.539
细1.537.5英制锥管螺纹和英制锥螺纹攻丝前钻底孔的钻头直径
英制锥管螺纹英制锥螺纹公称直每钻头直公称直每钻头直径25.4mm径径25.4mm径（\"）内牙数（mm）（\"）内牙数（mm） 1/8288.4 1/8278.6 1/41911.2 1/41811.1 3/8 3/81914.71814.5 1/2 3/414141111111118.323.629.738.344.155.8 1/2 3/41414111/2111/2111/2111/217.923.229.237.943.95611 1/41 1/2211 1/41 1/22
