A container of stainless brackets clears customs, reaches the buyer, and bounces straight back: wrong thickness, wrong finish, wrong grade. The parts weren't defective — they were mislabeled. Knowing how to label metal product specifications is what separates a supplier who gets reorders from one who eats return freight on perfectly good steel. And most of the labeling mistakes that lose export orders come from five beliefs that sound reasonable and are quietly wrong.
Metal is unforgiving on specs because "close enough" doesn't exist: a buyer's laser cutter, their weld procedure, their corrosion requirement all key off exact figures. Here are the five myths, and what to print instead.
Myth 1: "16 gauge is 16 gauge"
Gauge feels like a fixed size. It isn't. Gauge is a legacy numbering system, and the same gauge number means a different thickness depending on the metal — because steel, stainless, and aluminum use different gauge scales.
| 16 gauge in… | Actual thickness |
|---|---|
| Mild / carbon steel (MSG) | 1.518 mm |
| Stainless steel | 1.587 mm |
| Aluminum (Brown & Sharpe) | ~1.29 mm |
A buyer who orders "16 gauge" and receives a different metal's 16 gauge gets a thickness they didn't expect — and in sheet metal, tenths of a millimeter change the weld, the bend radius, and the price. The truth: gauge is not a unit. Always print the thickness in millimeters (and inches), with gauge as a secondary reference at most. "1.5 mm (16 ga, mild steel)" is unambiguous; "16 ga" alone is a guess the buyer has to make. This is a specific case of the broader nominal vs actual dimensions trap — the number everyone says out loud isn't the number the buyer can machine to.
Myth 2: "'Stainless steel' is a specification"
"Stainless steel" tells a buyer almost nothing. 304 and 316 look identical and behave completely differently: 316 has molybdenum and resists chloride corrosion (marine, coastal, chemical), 304 doesn't. A buyer sourcing parts for a seaside installation who receives 304 labeled only "stainless" has a corrosion failure coming, and they'll trace it back to your label.
Grade is the spec, and grade names differ by region — so print the grade and its standard:
| Common name | EN (Europe) | JIS (Japan) | Standard |
|---|---|---|---|
| 304 stainless | 1.4301 | SUS304 | ASTM A240 / EN 10088 |
| 316 stainless | 1.4401 | SUS316 | ASTM A240 / EN 10088 |
| A36 structural steel | S235JR (near-equiv) | SS400 (near-equiv) | ASTM A36 / EN 10025 |
The truth: a grade without its standard is half a spec. "304" means one thing under ASTM and its buyers should be able to cross-reference it to 1.4301 or SUS304; printing the standard number lets a buyer in any market confirm they're getting the alloy they need. Cross-region equivalents are "near," not exact — so name the standard you actually manufactured to.
Myth 3: "Surface finish is cosmetic, not a spec"
Suppliers treat finish as a looks question. For stainless, finish is a performance and price spec. The common cold-rolled finishes — 2B, BA, and No. 4 — are defined in ASTM A480 and they are not interchangeable:
- 2B — smooth, moderately reflective mill finish; the global default, best corrosion resistance for the price.
- BA (bright annealed) — brighter, more reflective mill finish; used where appearance matters.
- No. 4 — mechanically polished (brushed) finish; duller, and its corrosion resistance is actually lower than 2B or BA on the same grade because the abrasion exposes sulphide inclusions.
A buyer who ordered 2B and received No. 4 got a different corrosion profile and a different cost, even in the same grade. The truth: print the finish designation as part of the spec, not as an afterthought. "304, 2B finish" is a spec; "304, polished" is an invitation to a dispute over what "polished" meant.
Myth 4: "Nominal size is enough"
A buyer's fabrication process runs on tolerances, not nominal numbers. A plate labeled "3 mm thick" that arrives at 2.7 mm may be within one tolerance standard and out of another — and if you never stated which, the buyer decides after the fact, in their favor. General dimensional tolerances for metal parts are commonly specified with ISO 2768 (or GB/T 1804), which defines tolerance classes (f/m/c/v — fine to very coarse) so both sides know the allowable deviation before production, not after inspection.
The truth: state the tolerance or the tolerance class alongside the dimension. "Thickness 3.0 mm ± 0.2" or "linear dimensions per ISO 2768-m" turns a dispute into a checkable fact. This is exactly what a QC inspector verifies at pre-shipment inspection dimension checks — and an unstated tolerance is what turns a passing sample into a rejected shipment.
Myth 5: "One dimension tells the buyer the size"
Metal products are almost never described by a single number. A tube isn't "50 mm" — it's outer diameter × wall thickness × length, and the wall thickness is what decides whether it fits a fitting and how much load it carries. A sheet is thickness × width × length. An angle or channel is a full profile.
| Product | What "the size" actually is |
|---|---|
| Round tube / pipe | OD × wall thickness × length (OD ≠ ID) |
| Sheet / plate | thickness × width × length |
| Angle bar | leg × leg × thickness × length |
| Bar stock | diameter (round) or A/F (hex) × length |
The truth: give every dimension a buyer needs to fit and load the part, and label which is which. "Ø50 mm" leaves the buyer guessing whether that's outer or inner diameter — and for a tube, that guess determines whether their fitting slides on. Load-bearing metal parts carry the same labeling burden as any weight capacity in product images: the figure the buyer relies on has to be stated, sourced to a standard, and unambiguous.
What to Put on a Metal Spec Sheet
Pull the five fixes into one checklist the buyer can verify:
- Thickness in mm (and inches), gauge only as a secondary note with the metal named
- Grade + standard number (e.g., 304 / 1.4301 / SUS304, ASTM A240)
- Surface finish designation (2B, BA, No. 4) for stainless and coated products
- Tolerance or tolerance class on every critical dimension (e.g., ISO 2768-m)
- All dimensions the part needs — OD × wall × length for tube, thickness × W × L for sheet
- Both metric and imperial so buyers in any market read it without converting
- Figures marked on the product image itself, not buried in a separate datasheet
FAQ
How do I label metal thickness so buyers don't order the wrong size?
Print the thickness in millimeters (and inches), and treat gauge as a secondary note only. Gauge numbers map to different thicknesses for steel, stainless, and aluminum — 16 gauge is 1.518 mm in mild steel but 1.587 mm in stainless — so "16 ga" alone forces the buyer to guess. Marking "1.5 mm (16 ga)" directly on the product image, where the buyer looks first, removes the ambiguity that drives wrong-size orders and the returns that follow.
What information belongs on a steel or stainless spec sheet?
At minimum: thickness in mm, the grade with its standard number (304 / 1.4301 / ASTM A240), the surface finish for stainless (2B, BA, No. 4), a tolerance or tolerance class on critical dimensions, and every dimension the part needs to fit and carry load. Show metric and imperial together. Labeling those figures on the product image — rather than a separate PDF — is what lets a buyer confirm the spec at a glance; a dimension annotation tool that snaps the measured values onto the photo keeps them accurate and legible across markets.
Why do returns happen on metal products that aren't actually defective?
Because the parts don't match the label, not because they're faulty. Wrong thickness (gauge confusion), wrong grade (304 vs 316), wrong finish (2B vs No. 4), or an unstated tolerance all produce a shipment the buyer rejects even though the metal is sound. These are labeling failures, and they're expensive — you can put a number on the return freight and reorder cost with the return cost calculator.
Are steel grade names the same worldwide?
No. The same alloy carries different names by region: 304 stainless is 1.4301 in EN and SUS304 in JIS; A36 structural steel is close to S235JR in EN and SS400 in JIS. The equivalents are near, not exact, so always print the grade with the standard you manufactured to (ASTM, EN, or JIS) so a buyer in any market can confirm what they're getting.
Does surface finish affect more than appearance?
Yes. On stainless, finish changes corrosion resistance and cost. A No. 4 brushed finish actually has lower corrosion resistance than a 2B or BA mill finish on the same grade, because polishing exposes sulphide inclusions. Specifying the finish (2B, BA, No. 4) is a performance decision, not a cosmetic one, and it belongs in the spec.
Sources & References
- Sheet Metal Gauge Chart — gauge-to-mm conversions by metal — shows why the same gauge differs across steel, stainless, and aluminum
- ASSDA — 2B, 2D and BA cold-rolled finishes (ASTM A480) — definitions and properties of mill finishes
- ASSDA — No. 4: the workhorse finish — polished finish and its lower corrosion resistance
- ISO 2768-1:1989 — General tolerances for linear and angular dimensions — tolerance classes for parts without individual tolerance indications