The 30-Second Answer
Indoors, fresh water, food-safe
General fittings, brackets, shafts, kitchen and food-contact parts, architectural hardware. The default stainless — cheaper, everywhere, and fully adequate away from salt.
Salt, chemicals, medical
Marine and coastal hardware, pool equipment, chemical dosing, pharma and surgical parts. The 2% molybdenum stops pitting where 304 slowly gets eaten.
And one option the supplier blogs rarely mention: if your part is a turned component with no chloride exposure at all, free-machining 303 cuts several times faster than either — which directly lowers the part price. We flag this on quotes when the drawing says 304 but the application doesn't need it.
The Real Difference: 2% Molybdenum
Both are austenitic 18-8 family steels — roughly 18% chromium, 8–10% nickel, non-magnetic, not hardenable by heat treatment. 316 adds a minimum of 2% molybdenum, and that single addition is nearly the whole story: molybdenum defends the passive chromium-oxide layer against chloride attack, which is what causes the pitting and crevice corrosion that kills 304 in marine service. In a dry workshop, the two parts are indistinguishable for decades. Bolted to a boat, the 304 part shows tea-staining and pits in months.
| Property | 304 | 316 |
|---|---|---|
| Chromium / Nickel | ~18% / ~8% | ~16–18% / ~10–14% |
| Molybdenum | — | 2.0–3.0% |
| Tensile strength (annealed) | ~515 MPa | ~515 MPa |
| Yield strength | ~205 MPa | ~205 MPa |
| Chloride / pitting resistance | Fair | Very good |
| Bar stock cost | baseline | ~30–40% higher |
| EU designation | 1.4301 (A2) | 1.4401/1.4404 (A4) |
Mechanically they are near-twins — nobody should pick between 304 and 316 for strength. The decision is corrosion environment and budget, nothing else. (European drawings often say A2 for 304-class and A4 for 316-class fasteners — same decision, different labels.)
What It Does to Your Part Price
Here's the part the metal-supplier blogs get wrong by omission: the 30–40% premium applies to the raw bar, but on most machined parts the material is only a fraction of the price — machining time dominates. On a typical turned fitting or small bracket, switching 304 → 316 raises the finished part price by roughly 10–20%, not 40%. So if there's any real chance of chloride exposure, the insurance is cheaper than it looks. The reverse is also true: over-speccing 316 for an indoor bracket buys you nothing you'll ever see.
Machinability-wise both grades are gummy and work-hardening — 316 slightly more so, meaning a bit slower cutting and shorter tool life. An experienced shop handles both without drama; see our 304 machining and 316 machining pages for speeds, tolerances and finishing detail per grade.
Decision Guide by Application
- Marine hardware, deck fittings, coastal fixings → 316, no debate. See our marine parts work.
- Food processing → 304 for most contact surfaces; 316 where cleaning chemicals or brines are aggressive.
- Chemical, pharma, medical → 316 (316L if welded, to avoid sensitization at the weld).
- Indoor machine parts, brackets, shafts, general fittings → 304 — or 303 if it's a turned part and volume matters.
- Pool & spa equipment → 316; chlorinated water is exactly the attack molybdenum resists.
- High-volume turned fittings, no chlorides → 303 — cheaper per part than either, because it machines so much faster.
Not sure which grade your old part is? Send it to us. As part of reverse engineering we identify the material of worn or unmarked parts and quote a like-for-like replacement — with the grade decision explained, not just asserted.
What We See in Real Orders
Two patterns repeat. First: drawings that say 304 by default when the part is a turned fitting living indoors — we quote 304 as asked, and note the 303 alternative with its lower price so the buyer can decide. Second: marine customers burned once by 304 "stainless that rusted" — the fix is 316 plus, where the part is welded, the low-carbon 316L variant. Material certificates to EN 10204 3.1 ship with either grade on request, which matters if your QA needs traceability. If your comparison is actually stainless vs aluminum — a bracket that could be 6061 or even high-strength 7075 instead of steel — that trade-off (weight vs corrosion vs cost) is covered in our aluminum vs stainless guide.
304 vs 316 — FAQ
Molybdenum: 316 has ≥2%, 304 has none. That's what makes 316 resist salt water, pool chemicals and brines that pit 304. Strength is essentially identical.
Bar stock ~30–40% more — but on a finished machined part usually only 10–20% more, because machining time dominates the price of small parts.
Both are gummy and work-hardening; 316 is a little tougher on tools. For turned parts with no chloride exposure, 303 machines several times faster and is often the cheapest correct answer.
Yes — 304 is the standard food-grade stainless. Step up to 316 where cleaning regimes use aggressive chlorinated chemicals or the media is salty or acidic.
Yes — EN 10204 3.1 certs for the stock used plus dimensional reports, listed as line items on the quote when you ask for them in the RFQ.
Quote It in Both Grades
Send your drawing or sample — we'll quote 304 and 316 side by side (and flag 303 if it fits), so you decide with real numbers.