Self Tapping Thread Gauge Conversion Table.
Self Tapping Screws have a unique thread gauge classification. While they do use the same numbering system as imperial threads, the sizes within this series are not the same as the sizes for imperial UNF and UNC Threads.
For information on converting self-tapping thread sizes into metric measurements, please consult the table below.
| Self Tapping Thread Gauge Diameter | Thread Diameter (mm) | Threads per Inch (TPI) | Thread Pitch (mm) |
|---|---|---|---|
| No. 2 | 2.20 | 32 | 0.79 |
| No. 4 | 2.90 | 24 | 1.06 |
| No. 6 | 3.50 | 20 | 1.27 |
| No. 7 | 3.90 | 19 | 1.34 |
| No. 8 | 4.20 | 18 | 1.41 |
| No. 10 | 4.80 | 16 | 1.59 |
| No. 12 | 5.50 | 14 | 1.81 |
| No. 14 | 6.30 | 14 | 1.81 |
| No. 18 | 8.00 | 12 | 2.12 |
Due to the wide number of variations available under the broad classification of self-tapping screws, certain variants may have a coarser or finer pitch than the examples given here - the information above should be used as a guide only.