"Stainless steel" on a spec sheet tells you almost nothing. The grade — 304, 316 or 2205 duplex — determines whether your glass railing hardware still looks new after five winters beside a pool, or shows rust streaks after one. Here's the difference in plain language, with the numbers that matter.
304: the indoor grade
304 is the world's most common stainless steel — kitchen sinks, appliances, interior fittings. It contains chromium and nickel but essentially no molybdenum, the element that resists chloride attack. Indoors it's excellent. Outdoors near chlorine (pools) or salt (coastal air, de-icing salt), 304 typically develops "tea staining" and pitting within a few seasons. Fine for a mezzanine railing; a compromise anywhere wet or salty.
316: the usual "marine grade"
316 adds roughly 2–3% molybdenum, which meaningfully improves resistance to chlorides. It's the default recommendation for outdoor and coastal hardware, and it's a genuine step up from 304. Its PREN (Pitting Resistance Equivalent Number — the standard index of chloride resistance) sits around ~25, versus roughly 19 for 304.
2205 duplex: the specification grade
2205 is a duplex stainless — a mixed austenitic-ferritic structure with about 22% chromium, 3% molybdenum and added nitrogen. It's the alloy specified for offshore oil platforms, desalination plants and waterfront architecture. Two numbers tell the story:
- PREN above 35 — clearly higher than 316 (~25), meaning far better resistance to pitting from chlorine and salt.
- Yield strength of roughly 620+ MPa — about three times 304 (~210 MPa) and roughly double 316, so the same part is dramatically stronger.
What our lab testing showed
We had our 2205 duplex spigots independently tested (RELLAB Testing Services, report WX220418-013):
- Composition verified within the strict UNS S32205 / EN 1.4462 window — Cr 22.7%, Ni 5.2%, Mo 3.18%.
- 200 hours of neutral salt spray (ISO 9227:2017, 5% NaCl at 35°C): no significant surface change. Standard 304 typically shows visible corrosion well before the 200-hour mark in this test.
- Mechanical: 623 MPa yield, 825 MPa tensile, load-tested to 750 N/m on a 12 mm panel with deflection well inside allowable limits.
Which grade should you buy?
- Dry, indoor railing — 304 is acceptable; 316 buys margin.
- Outdoor deck or balcony (rain, Canadian winters, de-icing salt nearby) — 316 minimum; 2205 for zero-maintenance longevity.
- Pool fence, hot tub surround, coastal property — this is chloride territory: 2205 duplex is the grade actually specified for these environments.
One caveat: any stainless, including 2205, benefits from an occasional fresh-water rinse where salt or chlorine accumulates — corrosion resistance is not corrosion immunity.
See the tested hardware in our glass railing spigots collection, or start from your project in the pool fence and deck & balcony collections. Full test data is on the spigot product page.
