螺纹规格牙源距螺纹底孔直径M2标准0.401.60细牙0.251.75M2.5标准0.452.10细牙0.352.20M2.6标准0.452.20细牙0.352.25M3标准0.502.60细牙0.352.70M3.5标准0.603.00细牙0.353.20M4标准0.703.40细牙0.503.60M5标准0.804.20细牙0.504.60M6标准1.005.10细牙0.755.30M8标准1.256.80细牙11.007.10细牙20.757.30M10标准1.508.60细牙11.258.90细牙21.009.10细牙30.759.30M12标准1.7510.40细牙11.5010.60细牙21.2510.90细牙31.0011.10M14标准2.0012.20细牙11.5012.60细牙21.0013.10M16标准2.0014.20细牙11.5014.60细牙21.0015.10M18标准2.5015.70细牙12.0016.20细牙21.5016.60细牙31.0017.10螺丝的外径就是螺丝的公称尺寸，螺丝的内径＝螺丝的公称尺寸－螺距