Choosing the Right Rod for External Threads
Creating an external thread requires selecting the correct nominal diameter of the rod. A rod that is too thin will not allow full thread depth, while a rod that is too thick can make threading difficult and may damage the tool.
Recommended Rod Diameters for Metric Threads
| Thread | Pitch [mm] | Rod Diameter [mm] | Tolerance |
|---|---|---|---|
| M1 | 0.25 | 0.98 | -0.02 |
| M1.2 | 0.25 | 1.18 | -0.02 |
| M1.6 | 0.35 | 1.57 | -0.03 |
| M2 | 0.4 | 1.97 | -0.03 |
| M2.5 | 0.45 | 2.47 | -0.03 |
| M3 | 0.5 | 2.97 | -0.03 |
| M4 | 0.7 | 3.96 | -0.04 |
| M5 | 0.8 | 4.96 | -0.04 |
| M6 | 1.0 | 5.95 | -0.05 |
| M8 | 1.25 | 7.94 | -0.06 |
| M10 | 1.5 | 9.93 | -0.07 |
| M12 | 1.75 | 11.92 | -0.08 |
| M14 | 2.0 | 13.91 | -0.09 |
| M16 | 2.0 | 15.91 | -0.09 |
| M18 | 2.5 | 17.89 | -0.11 |
| M20 | 2.5 | 19.89 | -0.11 |
| M22 | 2.5 | 21.89 | -0.11 |
| M24 | 3.0 | 23.88 | -0.12 |
Preparing the Rod Before Threading
- Check the rod diameter with a caliper before starting
- Create a chamfer at the rod end to help the tool enter
- Remove burrs and sharp edges
- Use appropriate cutting fluid for threading
- For threads larger than M10, consider cutting in multiple passes
Methods for Making External Threads
- Manual threading: Suitable for small production and repairs. Use a set of dies (roughing and finishing).
- Lathe threading: Suitable for precise, long threads. Allows control over all thread parameters.
- Thread rolling: Chipless method for mass production. Produces stronger threads than cutting.