When you scroll through shiny floor drain photos online, they all look identical—until the first brown spot appears.
Behind every mirror finish hides a three-digit code: 201, 304 or 316.
Know the numbers, or pay for rust.
What the codes really mean
201: 17 % Cr, 4.5 % Ni, 6 % Mn – “budget blend” with manganese replacing expensive nickel.
304: 18 % Cr, 8 % Ni – the global workhorse.
316: 16 % Cr, 10 % Ni, 2 % Mo – marine-grade thanks to molybdenum.
Rust in real life
Independent salt-spray data (ASTM B117, public archive) show first red rust at:
201: 24 h
304: 168 h
316: 720 h
The magnetic trick
201 is strongly magnetic because of its Mn-rich structure.
Carry a pocket magnet on site; if the top plate clings like a fridge sticker, you know the supplier sneaked in 201 even when you paid for 304.
When is 201 “okay”?
Indoor, low-humidity, zero-chloride, rent-to-sell projects where the warranty ends at hand-over. For every wet room that sees deodorant, sweat or beach sand, insist on 304 minimum.
Where Each Steel Makes Sense
201: Budget hotel in desert climates, light-duty residential drains that will be replaced every 5–7 years.
304: 90 % of the world’s taps, drains and kitchen sinks. Safe up to 200 ppm chlorides (most city tap water sits below 50 ppm).
316: Indoor pools, beach-front condos, cruise ships, any place where chloride > 500 ppm or cleaning chemicals contain bleach.
So, are you ready to pick your stainless steel without looking back?
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