攻丝前钻孔直径

钻头直径就是标准底孔，最小直径和最大直径误差范围

螺纹尺寸钻头直径下孔径最小直径最大直径

3 × 0.5 2.5 2.59 (75%) 2.459 2.599

4 × 0.7 3.3 3.39 (80%) 3.242 3.422

5 × 0.8 4.2 4.31 (80%) 4.134 4.334

6 × 1.0 5 5.13 (80%) 4.91

7 5.153

8 × 1.25 6.8 6.85 (85%) 6.647 6.912

10 × 1.5 8.5 8.62 (85%) 8.376 8.676

12 × 1.75 10.3 10.40 (85%) 10.106 10.441

14 × 2.0 12 12.2 (85%) 11.835 12.210

16 × 2.0 14 14.2 (85%) 13.835 14.210

18 × 2.5 15.5 15.7 (85%) 15.294 15.744

20 × 2.5 17.5 17.7 (85%) 17.294 17.744

22 × 2.5 19.5 19.2 (85%) 19.294 19.744

24 × 3.0 21 21.2（85%）20.752 21.252