SS304 is a chromium-nickel stainless steel alloy, roughly 18% chromium and 8-10% nickel, used in most kitchen sinks because the chromium forms a passive oxide layer that stops rust. It's the same family of steel used in food processing equipment and surgical tools. This guide covers what the grade means, how it stacks up against SS201, what gauge measures, and the gauges RUMO uses across its own range.

What does the "304" in SS304 mean?

304 is a grade number set by an international steel classification system, and it identifies the alloy's composition rather than its thickness or finish. A 304-grade sheet contains iron as the base metal, roughly 18% chromium, 8-10% nickel, and small amounts of manganese and carbon. Chromium is the ingredient that matters most: it reacts with oxygen to form an invisible protective layer on the surface, and that layer re-forms on its own if the surface gets scratched. Nickel adds ductility, so the sheet presses into a sink bowl without cracking at the corners.

How does SS304 compare with SS201 and SS316?

SS304 sits in the middle of the three grades sold for sinks: SS201 is cheaper and less corrosion-resistant, SS304 is the standard choice for kitchens, and SS316 (marine grade) costs more and is rarely necessary indoors.

SS201 replaces roughly half the nickel with manganese to cut cost, and that trade-off shows up within a year or two as dulling or light staining, especially in hard water areas. SS316 adds molybdenum on top of the standard 304 recipe, which is why it holds up against salt air, but a domestic kitchen doesn't need that extra resistance. RUMO builds every sink in the range from SS304, not the cheaper 201 grade.

What is steel gauge and why does it matter?

Gauge is a number that describes the thickness of the steel sheet, and counterintuitively, a lower gauge number means a thicker, heavier sheet. An 18-gauge sink is thicker than a 22-gauge one, even though 18 is the smaller number. Thicker gauge steel resists denting under a dropped pan, flexes less when you lean on the drainer, and dampens the "tinny" ringing sound that thin sinks make when water hits the bowl. RUMO measures gauge in millimetres rather than the US gauge scale: 0.8mm, 1.0mm and 1.2mm cover the range, and the millimetre figure maps directly to sheet thickness with no conversion needed.

What gauge does RUMO use across its range?

RUMO's SS304 sinks run from 0.8mm to 1.2mm depending on the model, with the thicker gauge concentrated in the undermount range. The 5045 and 6045 undermount sinks use 1.2mm steel, the heaviest in the catalogue, chosen because undermount bowls carry their own weight without a worktop lip to help support them. The 6046 and 8044 undermount sinks use 1.0mm. On the inset side, models including Aurora, Prime Silver, Prime Black Charcoal, Artic, 8650, Essence Coruna, and 10050A use 0.8mm steel with reinforced R10 corners to compensate, and the darker finishes in the range add a nano coating on top of the steel for extra scratch resistance. Gauge isn't yet confirmed for five inset models pending supplier documentation, and RUMO won't publish a figure until it has one.

Does SS304 rust or stain?

No, SS304 doesn't rust under normal kitchen use, because the chromium oxide layer that forms on the surface is self-repairing and blocks the moisture that causes corrosion in plain steel. What looks like rust on a stainless sink is almost always a surface deposit rather than the steel itself corroding: limescale from hard water, or flash rust transferred from a rusty pan or scouring pad left sitting on the surface. Wiping the sink dry after use, and following the right cleaning routine, prevents both.

Is SS304 food-safe?

Yes, SS304 is food-safe, because it's non-porous, doesn't react with acidic foods, and is the same grade used in commercial kitchen worktops and food-processing lines. It won't leach into water or absorb odours from raw meat or fish the way a porous material can.

Shop silver stainless steel sinks built from 0.8-1.2mm SS304 steel across the RUMO range.