Stainless steel finish codes explained

At a glance

Codes from trade summaries of EN 10088-2; US names per IMOA. Check against BS EN 10088-2:2024 before quoting.

How to read the codes

Our journal articles on metal finishes and PVD steel finishes describe how these surfaces look and feel. This sheet adds what they leave out: the code system, the roughness figures and the wording that stops two people reading “brushed” differently.

• The first digit says how the sheet was rolled: 1 for hot rolled, 2 for cold rolled.
• The letter says what was done to the surface. B, D and R are mill finishes: the steel arrives that way. G, J, K and P are mechanical finishes (grinding, brushing, polishing) added afterwards. M is a pattern rolled in at the mill.
• US names (ASTM A480) such as BA, No.4 and No.8 are used by many suppliers and in many specifications. They line up with the EN codes as in the table above, but they are not identical systems, so quote both when it matters.
• Not every finish has a code. Hairline, fine non-directional and bead-blasted finishes sit outside the EN table, so they can only be fixed by description and an approved sample.
• Coarse finishes. 2G (US No.3) is a coarse ground finish and is left out of the table above. IMOA warns that rough finishes, coarse non-directional and ground patterns among them, are unsuited to corrosive or high-dirt areas unless cleaned regularly.

The standard was revised in September 2024 (BS EN 10088-2:2024). The trade sources we used describe earlier editions, so confirm the codes you quote against the current text.

Why “brushed” and “satin” are not specifications

The British Stainless Steel Association, drawing on the Euro Inox finishes guide, advises against using terms such as “brushed”, “satin polished” or “dull polished” on their own. It asks for finishes defined in EN 10088-2 on drawings, orders and quality documents, and for roughness (Ra, in micrometres) wherever possible, or a proprietary finish tied to a controlled roughness or an agreed reference sample. It says the same of the words grinding, polishing, brushing and buffing: they are not enough to define a finish.

Roughness is not a fixed property of a named finish. The International Molybdenum Association (IMOA) notes that the typical roughness of a finish varies from supplier to supplier and around the world, and advises asking the finisher for the typical Ra when samples are requested, then writing it into the specification. The chart below shows why: two trade-body tables give ranges that overlap and differ.

Grain direction and matching

Directional finishes (2J, 2K, hairline and most patterns) have a direction, and it must be on the drawing. Two adjacent panels with the grain turned through 90 degrees read as two different finishes, even from the same sheet.

• Vertical grain is the recommended orientation in IMOA's exterior guidance: it lets water and contaminants drain away, where horizontal grain tends to hold them. The same logic helps cleaning in interiors.
• Welds should be finished so their roughness is no greater than the surrounding finish (IMOA), and the finish should run through the weld line.
• Mill finishes do not always match. ASSDA notes that 2B roughness is largely set by the total cold-rolling reduction, so it differs between thicknesses, and that No.4 finishes from different suppliers are unlikely to match. Take sheets for one visible run from the same supplier and, where possible, the same batch.

Which finish where

These are studio suggestions for where to start sampling, not rules. The right finish depends on the lighting, the hand contact and the client's tolerance for visible wear, so always judge a physical sample.

Checking a sample before approval

• View it under the project's own lighting, at the real viewing distance, with the grain running the way it will be installed.
• Ask for the measured Ra of the sample, and record it next to the approval.
• Test it with real fingerprints and the cleaner the client will actually use.
• Keep one signed reference sample with the specification and one with the workshop; both are the benchmark if there is a dispute.
• If the finish will be PVD coated, approve the base finish first.

Stainless steel sheet, grade [1.4301 (304)], [2.0] mm. Finish [2J] to EN 10088-2 (edition [to be confirmed]), equivalent to US No.4. Typical Ra [0.2 to 0.6] micrometres across the grain on approved reference sample [ref. __]. Grain [vertical], identical on all panels and running through weld lines. Panels for one visible run from the same supplier and, where possible, the same batch. To match the approved sample under project lighting at [1] m.

Stainless steel sheet, grade [1.4401 (316)], [2.0] mm. Finish [2P] to EN 10088-2 (edition [to be confirmed]), equivalent to US No.8, polished then buffed. Polishing compounds to be stated by the fabricator and free of contaminants such as iron oxide. Welds dressed and polished to match, no rougher than the surrounding finish. Approved sample [ref. __]; no visible polishing lines or distortion at [1] m.

Stainless steel sheet, grade [1.4301 (304)], [1.5] mm. Finish [fine glass-bead blasted / pattern name and reference], non-directional matt [or pattern direction __]. Not defined by an EN 10088-2 code: defined by approved reference sample [ref. __] and its measured Ra [__] micrometres. Bead size and process to be stated by the fabricator.

Standards and sources

• BS EN 10088-2:2024: BSI, published 30 September 2024. Text not read; codes taken from summaries of earlier editions.
• British Stainless Steel Association: Surface finish: codes G, J, K, P; blasting; avoid specifying by brushed or satin.
• Euro Inox, Guide to Stainless Steel Finishes (BSSA-hosted): use Ra and EN 10088-2.
• IMOA: Which stainless steel should be specified for exterior applications?: Ra 0.5 or less; vertical grain.
• IMOA Stainless Solutions (August 2017): mechanically applied finishes: ASTM to EN cross-reference; Ra.
• ASSDA: Mill forms: 1D, 2D, 2B, BA; why Ra varies.
• Make Bespoke Studio journal: Metal finishes: how the finish families look and feel.

Questions we are asked

What is the difference between 2B and BA?

2B is the common smooth mill finish: cold rolled, annealed, pickled and skin passed, moderately reflective. BA, the EN code 2R, is bright annealed in a controlled atmosphere and is brighter and near mirror, though slightly milky and not a true polished mirror.

What is a No.4 finish in EN terms?

The closest EN code is 2J, brushed or dull polished; the finer 2K satin polish matches the US No.240. Because the word “brushed” does not fix the result, add a roughness figure, a grain direction and an approved sample.

Is a mirror finish the same as BA?

No. BA is a mill finish with no polishing lines. A mirror finish (EN 2P, US No.8) is made by polishing and buffing, and fine polishing lines can still be seen close up.

What roughness counts as smooth?

IMOA treats Ra 0.5 micrometres or less as smooth, in the context of exterior corrosion resistance. The same named finish can have a different Ra from different suppliers, so ask for the typical Ra with your samples.

Does bead-blasting have an EN code?

No. Bead and shot blasting fall outside the EN 10088-2 finish codes, so describe the finish, state a measured roughness and agree a reference sample.