304 vs. 316 Stainless Steel Screws
The difference is 2–3% molybdenum — and it decides whether your screws survive salt. 304 (18-8) handles inland weather for decades; within a few miles of the coast, around pools, or in chemical washdown, 316 is the minimum.
| Feature | 304 Stainless Screws | 316 Stainless Screws |
|---|---|---|
| Composition | 18% chromium, 8% nickel | 16% chromium, 10% nickel, 2–3% molybdenum |
| Also called | 18-8, A2 | Marine grade, A4 |
| Salt / chloride resistance | Stains and pits with prolonged salt exposure | Molybdenum blocks chloride pitting |
| Strength | Slightly higher tensile — irrelevant in wood, lumber fails first | Nearly identical in practice |
| Magnetism | Mostly non-magnetic | Non-magnetic |
| Cost | Baseline stainless | Roughly 30–60% more than 304 |
| Best for | Inland decks, trim, general exterior | Coastal, docks, pools, food and chemical areas |
Verdict
FAQ
Is 304 stainless OK for a deck?
Yes — inland. A 304 deck screw outlasts the deck boards away from salt. Go 316 only if you are coastal, poolside, or the deck sees de-icing salts every winter.
How close to the ocean before I need 316?
The common rule is within about 3 miles of salt water, closer if there is direct spray. Salt air pits 304 over years; 316 shrugs it off for decades.
What does 18-8 mean on stainless screws?
18% chromium and 8% nickel — the composition of grade 304. If a box says 18-8 and nothing else, it is 304, not 316.
Can I mix 304 and 316 screws in one project?
Mechanically yes — both are austenitic stainless so galvanic risk between them is negligible. Match grades anyway so everything weathers to the same finish.