The grain argument
In a cut thread the grain is severed at every root, so the root is effectively a series of stress concentrations. In a rolled thread the grain follows the thread profile, uninterrupted, which raises the torque needed to strip the thread and improves fatigue life at the root.
The diameter argument
Rolling displaces material outward, so the blank diameter is smaller than the finished major diameter. That is why a rolled thread has a slightly larger minor diameter and a better surface finish — and why the blank has to be sized correctly, not just the die.
When cutting is right
Very large diameters, threads that run into a shoulder with no run-out, and repairs all call for cutting. Rolling needs somewhere for the material to flow.
What to specify
Specify the thread standard and class, and say whether the thread is rolled. A supplier who rolls by default is usually a supplier who understands the fatigue case.
Rolled vs cut
| Property | Rolled | Cut |
|---|---|---|
| Grain at root | Continuous | Severed |
| Stripping torque | Higher | Lower |
| Fatigue life | Better | Worse |
| Surface finish | Better | Tool-marked |
If a joint strips before it should, check whether the thread was cut. It is one of the most common causes and one of the cheapest to fix.