Stainless “2B”, “BA” and “No.4” describe surface finishes, not grades. Pick by what the surface must do: stay clean, look bright, or hide fingerprints and scratches. If you care about cleanability, include a target Ra (roughness average) on the PO.
Quick definitions
- 2B: Cold‑rolled, annealed and pickled, then skin‑passed. Smooth, matte gray. Good base for polishing or painting.
- BA: Bright annealed in a controlled atmosphere. Shiny, reflective, tighter Ra than 2B. Shows scratches more readily.
- No.4 (satin/brushed): Mechanical polish with a visible grain (typically 150–240 grit). Hides handling marks better than BA.
Typical Ra ranges (guide)
| Finish | Typical Ra (μm) | Look | Common uses |
|---|---|---|---|
| 2B | ~0.3–0.6 | Matte, uniform | General fab, backs, substrates |
| BA | ~0.1–0.3 | Bright, reflective | Decor, appliances, liners |
| No.4 (180–240 grit) | ~0.6–1.2 | Satin with grain | Panels, guards, hand‑touch areas |
| 320‑grit satin | ~0.4–0.8 | Fine satin | Cleanable surfaces, handrails |
| Electropolished | ~0.2–0.5 (or better) | Bright, leveled | Food, pharma, high cleanliness |
Ranges vary by mill and thickness; always confirm your target with a sample or datasheet.
Choosing for your job
- Hygiene/cleanability: BA or fine satin (320) with an Ra target; electropolish for sanitary internals.
- Durable appearance: No.4 hides small scratches; protect with PE film during fab.
- Cost and flexibility: 2B for non‑visible faces or when you’ll polish later.
Fabrication tips
- Match the grain direction across adjacent panels for No.4.
- Use stainless‑only abrasives; avoid carbon‑steel contamination.
- Blend welds before final polish; passivate after welding to avoid tea stain.
Spec lines you can copy
- Backs and liners: 304 2B, Ra ~0.4–0.6 μm; film on one side.
- Visible panels: 304 No.4, 180–240 grit, Ra ≤1.0 μm; grain vertical; PE film; edges deburred.
- High‑cleanability: 316L BA, Ra ≤0.3 μm (OD); ID electropolished Ra ≤0.5 μm if fluid contact.
Tell us where the surface is used and how it’s cleaned. We’ll recommend the finish and Ra target, and send a small sample if needed.