Clock screw thread.
This thread was developed by engineer and university professor Thury from
Geneva before 1900.
The flank angle is 47.5°
| Thread No. | Major Diameter | Pitch | Tapping Drill Size |
| mm | mm | mm | |
| 0 | 6.000 | 1.000 | 4.800 |
| 1 | 5.290 | 0.900 | 4.220 |
| 2 | 4.660 | 0.810 | 3.728 |
| 3 | 4.110 | 0.729 | 3.224 |
| 4 | 3.620 | 0.656 | 2.808 |
| 5 | 3.190 | 0.590 | 2.492 |
| 6 | 2.810 | 0.530 | 2.164 |
| 7 | 2.480 | 0.480 | 1.924 |
| 8 | 2.180 | 0.430 | 1.684 |
| 9 | 1.920 | 0.390 | 1.432 |
| 10 | 1.640 | 0.349 | 1.280 |
| 11 | 1.490 | 0.310 | 1.128 |
| 12 | 1.320 | 0.280 | 0.964 |
| 13 | 1.160 | 0.250 | 0.900 |
| 14 | 1.102 | 0.230 | 0.724 |
| 15 | 0.901 | 0.210 | 0.648 |
| 16 | 0.794 | 0.190 | 0.562 |
| 17 | 0.699 | 0.170 | 0.496 |
| 18 | 0.616 | 0.150 | 0.440 |
| 19 | 0.543 | 0.140 | 0.372 |
| 20 | 0.479 | 0.120 | 0.336 |
| 21 | 0.426 | 0.110 | 0.288 |
| 22 | 0.372 | 0.099 | 0.252 |
| 23 | 0.328 | 0.089 | 0.223 |
| 24 | 0.289 | 0.080 | 0.194 |
| 25 | 0.254 | 0.072 | 0.164 |