英制螺纹底孔对照表如下：
| 英制螺纹 | 公制螺纹底孔直径（mm） |
| --- | --- |
| 1/8" UNC | 2.70 |
| 5/32" UNC | 3.30 |
| 3/16" UNC | 4.76 |
| 1/4" UNC | 6.35 |
| 5/16" UNC | 7.94 |
| 3/8" UNC | 9.53 |
| 7/16" UNC | 11.11 |
| 1/2" UNC | 12.70 |
| 5/8" UNC | 15.88 |
| 3/4" UNC | 19.05 |
| 7/8" UNC | 22.23 |
| 1" UNC | 25.40 |
| 英制螺纹 | 公制螺纹底孔直径（mm） |
| --- | --- |
| 1/8" NPT | 2.70 |
| 5/32" NPT | 3.30 |
| 3/16" NPT | 4.76 |
| 1/4" NPT | 6.35 |
| 5/16" NPT | 7.94 |
| 3/8" NPT | 9.53 |
| 7/16" NPT | 11.11 |
| 1/2" NPT | 12.70 |
| 5/8" NPT | 15.88 |
| 3/4" NPT | 19.05 |
| 7/8" NPT | 22.23 |
| 1" NPT | 25.40 |
这些数据可以帮助你在进行英制螺纹加工时，选择合适的公制螺纹底孔直径。