Why are rolled threads stronger?

Rolling does not cut the metal's grain; it bends it around the thread and work-hardens the surface, so rolled threads resist fatigue better.

What blank diameter is used for thread rolling?

Close to the thread's pitch diameter, not its major diameter, because the metal flows outward as it is rolled.

Can hardened parts be thread rolled?

Only up to about 35–40 HRC. Harder parts need thread grinding.

Thread rolling machine: types, capacity, uses

A thread rolling machine forms a thread by squeezing a round blank between hardened dies that carry the thread shape. No chips are made: the metal flows into the thread, which leaves it stronger and smoother than a cut thread. Two-die cylindrical machines roll studs, bolts and long threads; flat-die machines roll fasteners at very high speed.

Quick facts

Main types: Two-die cylindrical, three-die, flat die, planetary
Capacity: Rated by force (tonnes) and the largest diameter
Typical range: About M3–M64 on general machines
Speed: Seconds per part; flat-die machines much faster
Blank: Turned to about the pitch diameter
Materials: Steels up to about 35–40 HRC, stainless, brass

Main parts

Two or three die spindles (or two flat dies)
Hydraulic or mechanical infeed
Work rest that supports the blank
Feeding system for automatic loading
Coolant and lubrication

Two-die or flat-die?

	Two-die cylindrical	Flat die
Best for	Studs, long threads, varied sizes	Bolts and screws in huge volumes
Setup	Quick change	Longer
Thread length	Long (through-feed)	Short

Good to know

The blank diameter must be right, or threads come out too full or too thin
Rolled threads resist fatigue better than cut threads
Through-feed rolling makes threaded rod of any length

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Questions

Why are rolled threads stronger?: Rolling does not cut the metal's grain; it bends it around the thread and work-hardens the surface, so rolled threads resist fatigue better.
What blank diameter is used for thread rolling?: Close to the thread's pitch diameter, not its major diameter, because the metal flows outward as it is rolled.
Can hardened parts be thread rolled?: Only up to about 35–40 HRC. Harder parts need thread grinding.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 23 October 2026.