Thread Rolling vs Thread Cutting: The Strength Difference You Can Measure
Two screws with identical geometry can differ 20–50% in fatigue life depending on how their threads were made. The difference is cold work.
What rolling does
Thread rolling presses hardened dies against the blank, displacing material into the thread form. Nothing is removed: grains flow along the flank contours, the surface work-hardens, and compressive residual stress develops in the root — precisely where fatigue cracks start. Cut threads, by contrast, sever grains and leave tensile stress and tool marks at the root.
The measurable consequences
- Fatigue strength: rolled threads routinely beat cut ones by wide margins in repeated-load tests.
- Surface finish: rolling leaves smooth flanks — better friction consistency, better torque control.
- Material economy: no chips, faster cycle, cheaper per piece at volume.
When cutting still wins
Very small batches, oversized diameters beyond rolling-machine capacity, and some hard or exotic materials cut more practically than they roll. Blind-hole internal threads below certain sizes are cut because rolling taps cannot handle them. Topprecision rolls threads as standard on its production screws — including its 7-series aluminum bolt line, where the root's compressive layer is a key fatigue asset — and cuts only where volume or geometry demands.
