Stainless Steel Surface Finishes Explained
Mill finishes (No.1, 2D, 2B, BA) and polished finishes (No.3, No.4, hairline, No.8 mirror) compared per ASTM A480 and EN 10088-2 — with typical Ra ranges and how to choose the right one for your job.
Mill finishes vs polished finishes
A stainless steel finish is two things at once: how the surface looks, and how rough it is. The surface is created in two stages. Mill finishes come straight off the rolling line — hot rolling, annealing, pickling and (for cold-rolled sheet) a final skin-pass through bright rolls. Polished finishes are added afterwards by grinding, brushing and buffing with progressively finer abrasives. The number you choose drives appearance, hygiene, weldability, cost and lead time, so it belongs in your RFQ alongside grade and dimensions.
Standard finishes, Ra and typical use
Typical Ra ranges below reflect commonly published mill data for cold-rolled sheet and strip. Ra is not a fixed pass/fail figure in ASTM A480 for every finish — actual roughness varies with grade, gauge and producer, so always confirm against the mill test certificate.
| Finish (ASTM / EN) | How it is produced | Appearance | Typical Ra (µm) | Typical use |
|---|---|---|---|---|
| No.1 / 1D | Hot rolled, annealed, pickled / descaled | Dull, matte grey, non-reflective | 2.5–6.3 | Heavy plate, structural, heat exchangers, parts to be coated |
| 2D | Cold rolled, annealed, pickled | Uniform matte, low reflectivity | 0.4–1.0 | Deep-draw parts, painted/coated parts, industrial equipment |
| 2B | Cold rolled, annealed, pickled, skin-passed | Smooth, slightly reflective (light grey sheen) | 0.1–0.5 | The default general-purpose finish — fabrication, tube, food/process equipment |
| BA / 2R | Cold rolled then bright annealed in protective atmosphere | Bright, smooth, reflective (not a true mirror) | 0.05–0.1 | Appliances, decorative trim, hygienic and instrument parts |
| No.3 / 2G | Ground with coarse abrasive belts (~100–120 grit) | Coarse unidirectional grain, dull | up to ~1.0 | Heavy-duty equipment, surfaces to be further polished |
| No.4 / 2J | Brushed / polished with finer belts (~150–180 grit) | Fine satin unidirectional grain, low gloss | 0.2–1.0 | Architectural panels, sinks, food & sanitary equipment (cleanability baseline) |
| Hairline (HL) | Long, continuous fine grain lines (~150–320 grit) | Very fine, even hairline texture | 0.5–1.0 | Elevators, facades, decorative architecture |
| No.8 / 2P (8K) | Polished with successive fine grits then buffed | Mirror, non-directional, highest image clarity | ≤0.05 | Mirrors, signage, ornamental and reflective panels |
The four finishes buyers compare most
These are the names that come up in almost every enquiry. Here is the short version of how they differ.
Choosing a finish by application
Match the finish to what the part has to do, then to budget. As a rule, decorative work pulls toward brushed and mirror, hygiene pulls toward a low, controlled Ra, and structural work is happy with 2B or a plain brush.
| Application | Recommended finish | Why |
|---|---|---|
| Decorative / handrail / facade | No.4 brushed, hairline, or No.8 mirror | Consistent grain or high reflectivity; hides handling marks (brushed) or maximises shine (mirror) |
| Sanitary / food / pharma contact | Fine polish, low controlled Ra (No.4 or finer; electropolish where specified) | Smooth, crevice-free surface that cleans easily; No.4 is the common cleanability baseline |
| Structural / mechanical / general fabrication | 2B (or No.4 brushed where appearance matters) | Best value, welds and forms well, adequate corrosion resistance |
| To be painted, coated or further worked | No.1, 2D or pickled | Matte, keyed surface for adhesion; no point paying for a bright finish |
| Marine / chloride exposure | Smoother is better (BA, fine polish) on a 316/316L base | Lower Ra retains fewer deposits that drive pitting; grade matters more than finish here |
Finish and grade work together: a low-Ra surface helps corrosion resistance, but in aggressive chloride service the alloy does the heavy lifting — see our stainless steel grades guide and 316 industrial pipe for chloride and marine service.
Finishes we supply
As a manufacturer-direct mill in Foshan since 2006, ZAIHUI delivers the finishes most buyers ask for across 201, 304, 304L, 321, 316 and 316L, on welded or seamless product.
FAQ
What is a 2B finish?
2B is the most common cold-rolled mill finish: the steel is cold rolled, annealed, pickled and then given a light final pass (skin-pass) through polished rolls. The result is a smooth, slightly reflective light-grey surface with a typical Ra of about 0.1–0.5 µm. It is the general-purpose default for fabrication, tube and food/process equipment because it offers good appearance, weldability and value.
What is the difference between BA and 2B?
Both are cold-rolled mill finishes, but BA (bright annealed, EN 2R) is annealed in a protective atmosphere instead of being pickled, so it stays brighter and smoother — typically Ra 0.05–0.1 µm versus 0.1–0.5 µm for 2B. BA reflects clearly (though it is not a true mirror) and cleans more easily, while 2B is the lower-cost, slightly duller general-purpose choice.
Brushed (No.4) or mirror (No.8) — which should I choose?
Choose No.4 brushed when you want a uniform satin grain that hides fingerprints and handling marks — sinks, appliances, architectural panels and most food/sanitary work. Choose No.8 mirror when reflectivity and image clarity are the point, such as decorative panels, signage and ornamental trim. Mirror is the most expensive to produce and the easiest to scratch, so it usually ships with a protective film.
What does Ra mean and what is a good value?
Ra is the arithmetic average surface roughness in micrometres (µm); a lower number means a smoother, brighter, easier-to-clean surface. As a guide, mill 2B is roughly 0.1–0.5 µm, BA around 0.05–0.1 µm, No.4 brushed about 0.2–1.0 µm, and No.8 mirror ≤0.05 µm. There is no single "good" value — sanitary work needs a low controlled Ra, while structural parts are fine at 2B. Specify the Ra you actually need and confirm it on the mill test certificate.
Products and references
Need a specific finish?
Send your grade, gauge and finish (2B, BA, brushed or mirror) or a target Ra — we will confirm what ZAIHUI can supply, with protective film on request.