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Ring roller flat bar or round bar

Updated: 21 October 2026

You have mild steel on the bench, and the hand-crank ring roller either twists the bar or lets the rolls slip. A ring roller flat bar or round bar decision is which face sits in the curve. Flat on its thin edge, and small round bar inside the stated millimetres, are the pocket-crank jobs. Flat on its wide face, and round bar past those millimetres, need a different machine. Shelf prices are from amazon.co.uk on 20 October 2026 unless a UK trade page is named. Peter F. used those listings and public maker pages, not a lab test. A qualifying purchase can earn a commission at no extra cost to you. The kept listings are on the [ring roller comparison](/hub/painting-supplies/ring-roller).

You have mild steel on the bench, and the hand-crank ring roller either twists the bar or lets the rolls slip. A ring roller flat bar or round bar decision is which face sits in the curve.

Our top picks

KAKA INDUSTRIAL KAKA Industrial PR-3

Best overall

KAKA INDUSTRIAL KAKA Industrial PR-3
7.3/10about £185.63
View offer
Enborpe Enborpe KF-2437

Best value

Enborpe Enborpe KF-2437
0.0/10about £139.99
View offer
GYKOZY GYKOZY ring roller

Alternative

GYKOZY GYKOZY ring roller
0.0/10about £197.91
View offer
On this page
  1. 1.Two sections, and two ways to roll flat
  2. 2.What the rolls are doing
  3. 3.What the kept listings actually name
  4. 4.When to change machine

Two sections, and two ways to roll flat

The easy way puts the thin edge in the curve, like a belt around a pulley. The hard way puts the wide face in that plane, like a washer seen edge-on. AngleRoller uses that picture. The hard way needs grooves and a frame that does not let the rolls spring apart. Tool Reserve showed the Baileigh R-M5 at £576.65 as 25 × 7 mm the easy way and 20 × 6 mm the hard way. A crank of about 6 kg with one flat size and no hard-way line is an easy-way tool. Extra passes do not turn the wide face into the thin edge.

What the rolls are doing

Knurled rolls drive round bar by biting the surface, and those teeth mark aluminium. Flat bar wants a flatter face and a guide. The Metal Man RR-5G, an Australian page, prints a groove for 5 mm rod and flat at 25 × 3 mm. That is a pattern, not a UK price. Side guides are absent from the pocket listings here. Stakesys fits them on the STA143, with mild flat to 50.8 × 7 mm at £269 and £224.17. PR-3 reviews from the United States or Canada mention twist on some 1 in flat and knurl on aluminium.
KAKA INDUSTRIAL KAKA Industrial PR-3

Testsieger

KAKA INDUSTRIAL KAKA Industrial PR-3
7.3/10about £185.63
View offer

What the kept listings actually name

The KAKA Industrial PR-3 was about £185.63, at 6.21 kg, with the only star line, 4.4 from 133. It states 6.5 mm round, 25 × 4 mm flat, and rings from 3 in. That flat figure is the easy way, with no hard-way line and no side guides. Enborpe at about £139.99 names rebar and sheet, an unchecked title. GYKOZY at about £197.91 and CHENGLONG at about £237.72 print inch figures without separate flat, round, and minimum-diameter lines. For 12 mm rebar or hard-way flat, change class in the ring roller buying guide.

When to change machine

Another pass only repeats the same rolls. W. Neal Services lists the RR40 with separate lines for flat, round, square, and tube: 50 mm minimum for flat and 63 mm for round, at £150 subject to VAT. The STA143, with side guides and mild flat to 50.8 × 7 mm, is the step when the bar is wider than a pocket easy-way line. Box, channel, unknown stainless, and structural rings belong with a fabricator. Passes sit on how to use a ring roller.

Common questions

What is the easy way and the hard way?
The easy way bends flat bar on its thin edge, like a belt around a pulley. The hard way bends the wide face, like a washer seen edge-on. AngleRoller uses that picture, and the hard way needs grooves plus a stiffer frame because the bend runs across the full width. A pocket crank with one flat size and no hard-way line is an easy-way tool.
Can one set of rolls do both flat and round?
A narrow set can drive small round bar in a groove and light flat bar the easy way. The Metal Man RR-5G separates a 5 mm rod groove from 25 × 3 mm flat. Knurl still marks aluminium and can twist flat bar if nothing holds the edge. The PR-3 states 6.5 mm round and 25 × 4 mm flat, without side guides. Past those sizes you need another machine.
Why does flat bar twist?
Flat bar twists when the rolls drive it and the wide face can rotate out of the bend. Knurl, cut for round bar, makes that worse. PR-3 reviews from the United States or Canada describe twist on some 1 in flat. The Stakesys STA143 uses side guides so the bar does not wander and coil.
Will knurled rolls mark aluminium rod?
Yes. Teeth that grip steel rod print into aluminium, and PR-3 owners in the United States or Canada report that mark. Bright aluminium that must stay clean wants a smoother roll, even when the diameter is inside the steel figure. Mild steel hides the pattern. A flatter roll spares the surface and drives round bar less well.
What minimum diameter changes between flat and round?
The smallest ring changes with the section. The W. Neal Services RR40 page gives 50 mm for flat and 63 mm for round, with square and tube on their own lines. The flat figure will not plan a round ring. The PR-3 states rings from 3 in. That is a pocket-crank figure, not the RR40 table.
Is 12 mm rebar the same job as 6 mm round bar?
No. Smooth 6 mm mild rod sits beside the PR-3 line of 6.5 mm round. Ribbed 12 mm rebar is thicker and a different section. The Enborpe KF-2437, about £139.99, names rebar in the title, and that title is not a checked capacity table. Plan 12 mm on a machine whose published round-bar line includes it.
When do I need a different machine rather than more passes?
You need another machine when the section is outside a published mild-steel line. Hard-way flat, round bar past the stated millimetres, box, channel, and structural rail stay wrong on the same crank. A manual with separate minimums, or the STA143 with guides at £269 or £224.17, is the step for heavier bar. Structural rings belong with a fabricator.

Related pages

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Ring roller buying guide: match the mild-steel bar

How to use a ring roller: passes, lead and the nip

Sources

Public UK sources used for this comparison. Listing prices, stars and review counts are the amazon.co.uk figures saved for this set on 20 October 2026. Trade prices below are not amazon.co.uk prices.

  1. HSE EIS7, Safe use of 3-roll bending machines (retrieved 20 October 2026)
  2. HSE, PUWER overview (retrieved 20 October 2026)
  3. GOV.UK, Product safety advice for businesses (retrieved 20 October 2026)
  4. GOV.UK, Supply of Machinery (Safety) Regulations 2008 (retrieved 20 October 2026)
  5. GOV.UK, UKCA and CE marking by sector (retrieved 20 October 2026)
  6. W. Neal Services, WNS heavy duty manual ring roller (retrieved 20 October 2026)
  7. DIMAKIN, Ring roller RM-602 (retrieved 20 October 2026)
  8. Consumer Rights Act 2015 (retrieved 20 October 2026)