---
title: "What Is a Bright Bar? Types, Tolerances, Sizes and Uses"
source: "https://www.laxconsteels.com/bright-bars-everything-you-need-to-know/"
description: "How cold drawing, peeling and grinding set bright bar tolerances, surface finish and straightness, with sizes from 5 to 115 mm and common uses."
---
# Bright Bars: Tolerances, Finishes and Supply Conditions

Published 28 June 2024 Updated 8 September 2026 10 min read

A [bright bar](https://www.laxconsteels.com/products/bright-bars/) is a hot rolled steel bar that has been cold finished at room temperature to a defined surface condition and dimensional tolerance. Bright bar is not a grade of steel: the chemical composition is that of the ordered grade and is identical to the same grade supplied as black bar. The commercial specification of a bright bar therefore rests on its tolerance class and finishing route rather than on its chemistry, and two bright bars of the same grade and diameter can differ substantially in cost according to which tolerance class was held and which route produced it. The classes themselves are tabulated in the [tolerance class reference](https://www.laxconsteels.com/stainless-steel-bar-tolerance-classes/), and the choice against hot rolled bar is set out in [bright bar vs black bar](https://www.laxconsteels.com/bright-bar-vs-black-bar/).

## Cold finishing

Hot rolling forms a bar above its recrystallisation temperature. The process leaves a black scaled surface, an open dimensional tolerance and a decarburised skin. Cold finishing, carried out at room temperature, addresses all three. Laxcon operates 15 bar processing and finishing lines running five cold finishing routes.

| Route | What happens | What it is good at |
| --- | --- | --- |
| Cold drawing | The bar is pulled through a die that reduces the section | Cheapest route to a bright surface and a close tolerance. Raises tensile strength and lowers ductility through work hardening |
| Peeling, then polishing | A rotating head cuts the outer skin away, then the surface is polished | Removes the decarburised layer and any rolling defect with it. The route normally used at larger diameters |
| Rough peeling | Peeled and left | A clean, defect-free surface where the customer will machine anyway |
| Smooth turning | Turned on a machine rather than drawn | Sizes and lengths that do not suit a draw bench |
| Centreless grinding | Ground between a control wheel and a grinding wheel | The closest tolerances and the best surface. The most expensive route |

Cold drawing work hardens the bar. A drawn bar has higher tensile strength and lower ductility than the same grade in the annealed condition, and the difference is not visible. Where the mechanical properties are required to be those of the annealed grade, the bar is annealed after drawing. The delivery condition stated on the test certificate records which condition applies.

## Tolerance classes

The tolerance classes published for Laxcon bright bar are h7, h8, h9, h10, h11, k12, k13 and ASTM A484. In each ISO designation, the number is the ISO 286 tolerance grade and sets the width of the tolerance band; the letter sets the position of that band relative to the nominal size.

For an h class the upper deviation is zero: the bar is never larger than nominal and can only be undersize. For a k class at grade 12 and above the lower deviation is zero: the bar is never smaller than nominal and can only be oversize. The distinction is functional. An h bar of a given nominal size fits into a bore that a k bar of the same nominal size does not.

### The classes in millimetres

The following table gives the total tolerance band in microns, taken from ISO 286, across the supplied diameter range.

| Diameter | h7 | h8 | h9 | h10 | h11 | k12 | k13 |
| --- | --- | --- | --- | --- | --- | --- | --- |
| over 3 to 6 mm | 12 | 18 | 30 | 48 | 75 | 120 | 180 |
| over 6 to 10 mm | 15 | 22 | 36 | 58 | 90 | 150 | 220 |
| over 10 to 18 mm | 18 | 27 | 43 | 70 | 110 | 180 | 270 |
| over 18 to 30 mm | 21 | 33 | 52 | 84 | 130 | 210 | 330 |
| over 30 to 50 mm | 25 | 39 | 62 | 100 | 160 | 250 | 390 |
| over 50 to 80 mm | 30 | 46 | 74 | 120 | 190 | 300 | 460 |
| over 80 to 120 mm | 35 | 54 | 87 | 140 | 220 | 350 | 540 |

A worked example illustrates the bands. A 40 mm bar at h9 measures between 40.000 and 39.938 mm. The same bar at h11 measures between 40.000 and 39.840 mm, a band two and a half times as wide. At k12 the bar measures between 40.000 and 40.250 mm. A k12 bar therefore cannot be fitted as delivered into a 40 H7 bore.

The tolerance class also determines the finishing route, and with it the cost: h7 and h8 are produced on a grinding line, h9 and h10 on a drawing or peeling line, and h11 and the k classes are held by a straightened and lightly finished bar.

## Surface finish and straightness

The published surface finish is Ra 0.2 micron maximum, equivalent to 8.7 RMS. Published straightness is up to 0.5 mm per metre. Grit polishing is available at K240 or K320 or to a stated requirement.

Surface roughness governs fatigue life, because fatigue cracks initiate at surface features, and it affects corrosion resistance, because a rougher surface retains more contaminant and passivates less evenly. Straightness governs whether a bar can be fed through a machine: a bar bowed beyond the tolerance of a bar feeder whips during rotation.

Where straightness better than 0.5 mm per metre is required, the applicable product is a [precision shaft quality bar](https://www.laxconsteels.com/products/precision-shaft-quality-psq-bars/), published at 0.015 inch total indicator reading per 10 feet. The difference between the two products is set out in [a separate article on PSQ bars](https://www.laxconsteels.com/everything-about-psq-bars-types-uses-and-selecting-the-right-manufacturer/).

## Size range and profiles

| Product | Size range | Length | Tolerances |
| --- | --- | --- | --- |
| [Round bright bars](https://www.laxconsteels.com/products/bright-bars/) | 5 mm to 115 mm | up to 6.5 m | h7 to h11, k12, k13, ASTM A484 |
| [Square bright bars](https://www.laxconsteels.com/products/square-bright-bars/) | 12.70 mm to 55 mm | up to 6 m | h11, k12, k13, ASTM A484 |
| [Hexagonal bright bars](https://www.laxconsteels.com/products/hexagonal-bright-bars/) | 15 mm to 52 mm across flats | up to 6 m | h11, k12, k13, ASTM A484 |
| [Cold drawn flat bars](https://www.laxconsteels.com/products/cold-drawn-flat-bars/) | 20 mm to 80 mm width | 2 m to 6 m | h11, ASTM A484 |

Only the round bar is offered below h11. Squares, hexagons and flats are drawn products, and a drawn profile does not hold a ground tolerance; the published class for these profiles is accordingly h11 and coarser.

Square and hexagon sizes are listed twice on their product pages, once for drawn stock and once for black or HRAP stock, and the two lists differ. The drawn list is the finished size after the die; the black or HRAP list is the hot rolled starting stock, which runs to larger sizes because it has not been reduced. A part is ordered from the drawn list when it is used at the delivered size and from the black list when it will be machined down. Weight per metre for all four profiles is given on the [weight charts](https://www.laxconsteels.com/weight-charts/). The weight of a square is the side squared multiplied by 0.0079, and a hexagon weighs 86.6 percent of the square of the same size across flats, its area being the square's multiplied by root three over two.

## Ends, heat treatment and testing

- **Ends.** Chamfered at 30, 45 or 60 degrees, or plain without burrs or sharp edges. A chamfer is relevant where the bar enters a bar feeder or a collet.
- **Heat treatment.** Soft annealing, solution annealing, oil and water quenching, tempering and ageing. Heat treatment sets the mechanical properties, which belong to the delivery condition rather than to the grade.
- **Eddy current testing.** Available to the customer's requirement. There is no default; the test appears on the certificate only when it was on the order.
- **Grade confirmation.** Handheld spectrometers provide positive material identification on the piece rather than on a cut sample.
- **Declarations.** Freedom from radioactive elements, mercury and lead contamination, supported by screening of incoming scrap with a Rad Eye meter before it reaches the furnace.
- **Standards.** EN, DIN, JIS, ASTM, BS, ASME, GOST and AISI, including NACE MR0175 and MR0103 where sour service applies.

## Specifying a bright bar order

Five items make a bright bar order unambiguous.

1. **Grade and standard.** A grade named to one standard rather than as an equivalent. AISI 304 and DIN 1.4301 do not share a chromium window, as set out in [a separate guide to grade 304](https://www.laxconsteels.com/304-stainless-steel-quality-guide-why-its-industry-standard/).
2. **Diameter and tolerance class.** The class itself, not the word bright. The tolerance class has the largest single effect on price.
3. **Finishing route or surface requirement.** Ground, drawn, peeled and polished, or a stated Ra figure.
4. **Delivery condition.** As drawn, or annealed after drawing. The two conditions have different mechanical properties.
5. **Testing.** Eddy current, ultrasonic, intergranular corrosion or impact testing. A test not stated on the order does not appear on the certificate.

## Frequently asked questions

### What is the difference between a bright bar and a black bar?

Black bar is hot rolled and leaves the mill with a scaled surface at an open tolerance. Bright bar has been cold finished at room temperature, giving a clean surface and a close tolerance. The two are the same steel, produced by different processes at different prices.

### Which tolerance class should be specified?

The appropriate tolerance is the coarsest class the part accepts. A bar entering an assembly with no further machining must match the fit, which typically requires h7 or h8. A bar that will be machined can be ordered at h11 or a k class, since machining removes the difference and the finer class carries an unnecessary cost.

### What does k12 mean, and why is it larger than nominal?

The k prefix places the tolerance band on the plus side of nominal, so the bar is at or above the stated size. It is used where the bar must clean up to a finished size in later machining, and it is unsuitable where the bar has to fit a bore as delivered.

### Is bright bar stronger than black bar?

In the as drawn condition, bright bar is stronger than black bar, because cold work raises tensile and yield strength while reducing ductility. Annealed after drawing, it is not. The delivery condition on the certificate identifies which condition applies, and the mechanical figures on the certificate belong to that condition.

### What sizes do you supply?

Laxcon supplies round bright bar from 5 mm to 115 mm in lengths up to 6.5 metres. Squares from 12.70 mm to 55 mm, hexagons from 15 mm to 52 mm across flats, and cold drawn flats from 20 mm to 80 mm wide are supplied in lengths up to 6 metres. Above 115 mm the applicable product is [proof machined bar](https://www.laxconsteels.com/products/forged-proof-machined-bars/), supplied from 120 mm to 550 mm.

### Can bright bars be supplied in 316 and duplex?

Bright bars are supplied in 316 and in duplex grades. The finishing lines are grade agnostic; the grade changes the machinability and therefore the cost. Duplex and the higher-alloy austenitic grades work harden more strongly and are processed at lower speeds.

## Sources

Size ranges, tolerance classes, surface finish, straightness, grit polish, end finishes, heat treatments, testing and declarations are the published supply conditions on the [bright bars](https://www.laxconsteels.com/products/bright-bars/), [square bright bars](https://www.laxconsteels.com/products/square-bright-bars/), [hexagonal bright bars](https://www.laxconsteels.com/products/hexagonal-bright-bars/) and [cold drawn flat bars](https://www.laxconsteels.com/products/cold-drawn-flat-bars/) pages. Finishing line equipment is on the [technology page](https://www.laxconsteels.com/technology/). Weight per metre and the section coefficients are on the [weight charts](https://www.laxconsteels.com/weight-charts/). Composition windows are in the [grade reference](https://www.laxconsteels.com/grades/). The tolerance grade values in microns are the ISO 286 standard values, which are published reference data rather than Laxcon measurements.