M3 to M75 Thread Ranges — Complete Guide to Thread Rolling Machine Selection

Thread size is the single most important factor in selecting a thread rolling machine. Get it right and your machine runs efficiently for decades. Get it wrong and you either cannot produce the parts you need, or you are operating an oversized, costly machine on small work that could have been handled by a simpler setup. This guide walks through the full metric thread range from M2 to M75 and maps each size to the appropriate machine type.

Why Thread Size Matters in Machine Selection

Thread rolling is a cold-forming process — the die rolls must displace metal to form the thread. Larger threads require more force and a more robust die roll arrangement. A machine designed for M8 simply cannot develop the hydraulic force needed to cold-form M36 — and a machine designed for M75 would be wasteful and imprecise on M6 work. The three machine types in Hardev Hydraulics' range each have an optimum size envelope.

Thread tolerances also scale with size. ISO metric thread standards define separate tolerance classes (6H for nuts / internal, 6g for bolts / external) for each pitch. Larger pitch threads at larger diameters require more precisely controlled forming force — which is why larger machines use hydraulic closed-loop pressure feedback rather than simple mechanical stops.

M2–M8 Range: Flat Die Thread Rolling Machine

The Flat Die machine is the definitive solution for the small-fastener size range. Two hardened flat dies — one stationary (fixed die) and one reciprocating (moving die) — move in opposite linear directions. Blanks are fed between the dies, and as the moving die passes across the blank's length, the thread form is impressed in a single linear stroke.

Key size parameters in this range:

• M2 × 0.4 pitch — machine screws, electronic hardware, precision instruments
• M3 × 0.5 pitch — small fasteners, optical equipment, fine mechanism screws
• M4 × 0.7 pitch — general machine screws, PCB standoffs
• M5 × 0.8 pitch — appliance hardware, bicycle components
• M6 × 1.0 pitch — the most common small fastener globally; automotive, consumer products
• M8 × 1.25 pitch — upper limit for flat die; structural small bolts, machinery

Typical applications: Screw manufacturing plants, hardware export units, electronic sub-assembly suppliers, bicycle and cycle-rickshaw component manufacturers (a major Ludhiana industry).

Production speed: 150–320 pieces per minute with auto-feed — far faster than any cylindrical die alternative at this size class.

M3–M45 Range: Two Roll Thread Rolling Machine

The Two Roll cylindrical die machine handles the broad mid-range of metric threads that covers the majority of India's fastener output. Two cylindrical die rolls are mounted on parallel spindles. The workpiece blank is held between them and the rolls infeed radially under hydraulic pressure — the thread form being rolled simultaneously across the full blank length in each cycle.

Key size parameters in this range:

• M3–M6 — overlap with flat die; Two Roll preferred when thread length exceeds die plate length
• M8 × 1.25 — general-purpose hardware; bolts, set screws
• M10 × 1.5 — beginning of the heavy fastener range; automotive, structural
• M12 × 1.75 — most common structural bolt size in Indian construction
• M16 × 2.0 — structural bolts, foundation anchor bolts
• M20 × 2.5 — heavy structural connections, machinery mounting bolts
• M24 × 3.0 — large structural bolts, civil engineering
• M30 × 3.5 — heavy machinery, pressure vessel studs
• M36 × 4.0 — scaffolding tie rods, anchor systems (also covered by Three Roll)
• M42 × 4.5 — mining bolts, heavy industry
• M45 × 4.5 — upper limit for Two Roll; large flange studs

Typical applications: Fastener manufacturers in Ludhiana, Jalandhar, Rajkot; auto-component bolt plants; stud bolt manufacturers for oil and gas; tractor and farm equipment hardware.

Production speed: 20–65 pieces per minute depending on size and material. Hydraulic force: 36 metric tons. Spindle speed: 20–120 RPM.

M10–M75 Range: Three Roll Thread Rolling Machine

The Three Roll (planetary) machine wraps three die rolls at 120° around the workpiece, providing perfectly balanced radial force from three points simultaneously. This balanced force arrangement eliminates the bending moment that a two-point contact system imposes on large-diameter, long workpieces — making it the correct choice for M46+ and strongly preferred for long parts above M30.

Key size parameters in this range:

• M10–M45 — overlap with Two Roll; Three Roll preferred for long studs and bars where straightness is critical
• M36 × 4.0 — scaffolding tie rods, jack prop inner tubes
• M42–M52 — jack prop and acrow prop outer tube threading; heavy anchor bolts
• M56 × 5.5 — large industrial anchor bolts, mining rock bolts
• M64 × 6.0 — heavy civil engineering, dam and bridge anchors
• M72–M75 × 6.0 — upper limit of Three Roll; special heavy industry and infrastructure applications

Typical applications: Scaffolding and prop manufacturers, anchor bolt producers for infrastructure, mining rock bolt manufacturers, rebar threading for post-tensioned concrete, prestressed concrete component suppliers.

Production speed: 15–45 pieces per minute. Hydraulic force: 22 metric tons (balanced across three rolls = effective forming force of 66 metric tons total). Handles ISO, DIN, BSP, UNC/UNF thread forms.

The Overlap Zone: M10–M45

Both the Two Roll and Three Roll machines can produce threads in the M10–M45 range. Which machine to use in this overlap zone depends on:

• Workpiece length: For bolts shorter than 150 mm, Two Roll is more economical. For long bars, rods and studs above 200 mm, Three Roll's balanced force gives better straightness retention.
• Concentricity requirement: If thread concentricity to a ground journal (as in precision studs) is critical, Three Roll is preferred.
• Volume: Two Roll is faster in this range (20–65 pcs/min vs 15–45 pcs/min for Three Roll), so for pure speed, Two Roll wins at M10–M45.
• Material hardness: Harder materials (alloy steels) at larger diameters benefit from Three Roll's balanced force — less tendency to deflect the blank during rolling.

Tolerance Standards: ISO 6H/6g

All Hardev Hydraulics thread rolling machines produce threads to ISO metric tolerance class 6g (external thread / bolt) as standard — the most widely specified commercial tolerance for general-purpose threaded fasteners. Tighter tolerances (4g, 4h for precision applications) are achievable by careful die profile preparation and hydraulic pressure calibration.

Thread rolling inherently produces more consistent tolerance compliance than cutting, because the die roll profile wears gradually and uniformly — unlike a cutting tool that can chip or deflect suddenly. Our PLC-controlled machines compensate for die wear by monitoring forming force and adjusting roll gap automatically.

Non-Metric Thread Forms

Beyond ISO metric, Hardev Hydraulics' machines can produce UNC and UNF unified threads (common in defence and export fasteners), BSP/BSPP pipe threads, and trapezoidal (TR) and ACME forms for lead screws and jacks — depending on the die set supplied. Contact us with your specific thread form requirement for confirmation.