Galvanized vs Stainless Fasteners: Corrosion, Strength, Cost
Hot-dip galvanized vs stainless steel fasteners — corrosion mechanisms, treated-lumber and coastal rules, strength grades, galling, and cost.
Updated August 20, 2026
Galvanized and stainless fasteners fight corrosion with opposite strategies. A hot-dip galvanized bolt is ordinary steel wearing a sacrificial zinc suit: the zinc corrodes first, by design, and protects the steel even where the coating gets scratched — until the zinc is spent. A 300-series stainless fastener is corrosion-resistant through and through: chromium in the alloy forms a self-healing oxide film, so there is no coating to consume, cut through, or wear out.
Modern preservative-treated lumber is what turned this from a price question into a specification question. Copper-based treatments (ACQ, copper azole) are markedly more corrosive to steel and zinc than the old CCA formula, and connector-industry guidance now draws the line explicitly: hot-dip galvanizing to ASTM A153 is the minimum for ordinary treated-wood contact in dry service, while high retention levels, ground contact, and anything within reach of salt air step up to Type 304/305/316 stainless.
The stainless premium buys chemistry, not strength — common 300-series fastener grades sit near mild-steel strength, well below hardened structural bolts — and it introduces its own quirks: thread galling, and a galvanic penalty when stainless and galvanized parts are mixed in the same wet joint. The rows below sort those trade-offs by exposure.
Side by Side
| Spec | Hot-dip galvanized | Stainless steel (300 series) |
|---|---|---|
| Corrosion protection mechanism | Sacrificial zinc layer, metallurgically bonded by the hot-dip bath — protects scratches galvanically until the zinc is consumed | Passive chromium-oxide film through the full cross-section — self-healing, nothing to wear away |
| Governing standards | ASTM A153 / F2329 (hot-dip zinc coating on hardware and fasteners) | ASTM F593 (bolts/screws/studs) and F594 (nuts), Alloy Groups 1–2 covering 304/305/316 |
| Preservative-treated lumber contactPer Simpson Strong-Tie published corrosion guidance; treatment chemical and retention level, not just "treated wood," drive the requirement. | The published minimum for today’s copper-based treatments at standard retentions in dry service — thin electroplated zinc is not acceptable | Recommended by connector-maker guidance for high chemical-retention levels and treated wood in ground contact |
| Coastal / salt exposure | Zinc is consumed quickly in salt spray — a finite-life choice near the ocean | The standard recommendation on and near coastlines, with Type 316 preferred in the splash zone for its molybdenum-enhanced chloride resistance |
| Strength grade availability | Full structural range — A307 through high-strength structural bolts are routinely hot-dip galvanized (the hardest grades excepted for hydrogen-embrittlement reasons) | Common F593 conditions land near mild-steel strength; high-strength stainless exists but is specialty-priced — do not assume Grade 5/8 equivalence |
| Galling & seizing behavior | Rare — zinc acts as a modest lubricant, though the thick coating needs oversized (tapped-oversize) nuts | Notorious — stainless-on-stainless threads cold-weld under speed and pressure; anti-seize or lubricant is standard practice |
| Appearance & staining | Dull gray, weathers to matte; can leave gray runoff streaks and reacts with tannin-rich woods | Bright and stays bright; the default where fastener heads show — and the only choice that avoids black tannin staining on cedar and redwood |
| Relative cost drivers | The economical exterior baseline — modest premium over plain steel | Several times the galvanized price, scaling with alloy (316 over 304) and diameter |
Which One for the Job
Ground-contact pressure-treated deck framing
Stainless steel (300 series)
Ground-contact lumber carries the high preservative retentions for which connector-industry guidance explicitly recommends stainless: the wood stays wet, the copper-based chemistry keeps attacking zinc, and a consumed coating cannot be reapplied inside a joint. Hot-dip galvanized remains defensible only for the dry-service, standard-retention parts of the structure.
Oceanfront railing and deck hardware
Stainless steel (Type 316)
Salt spray is the environment zinc dies fastest in and the one 316’s molybdenum addition exists for. Published coastal guidance from both the galvanizing and connector industries converges here: within salt-air reach, specify stainless, and within the splash zone specifically 316 — the corrosion allowance of galvanizing is measured in years, the maintenance access often in decades.
Indoor structural bolting
Hot-dip galvanized (or plain steel)
Dry interior service barely taxes zinc at all, and structural strength grades are cheap and standard in galvanized while stainless equivalents are specialty items well below hardened-bolt strength. Paying the stainless multiple indoors buys shine, not service life.
Cedar or redwood siding and trim
Stainless steel (300 series)
Tannin-rich woods react with zinc and iron to leave permanent black streaks bleeding from every fastener head — a cosmetic failure no coating thickness prevents once weathering opens it. Stainless is the published siding-industry answer for these species, and on a visible facade the premium per fastener is trivial against the cost of staining the cladding.
Frequently Asked Questions
Can galvanized and stainless hardware be mixed in one connection?
Not in wet service. Stainless is strongly cathodic to zinc, so in a damp joint the pairing turns the galvanized part into a sacrificial anode and strips its coating at an accelerated rate — a stainless bolt through a galvanized hanger consumes the hanger’s protection. Keep each connection all one metal class, matching fastener to connector, which is exactly how connector catalogs specify it.
Why do stainless nuts sometimes lock solid while being tightened?
Thread galling: stainless’s protective oxide scrapes off under thread pressure, bare metal cold-welds, and the nut seizes mid-thread — often ruining both parts. It is a stainless-on-stainless phenomenon, worst with power drivers and long thread engagement. The standard countermeasures are anti-seize compound, slow hand tightening, and pairing different stainless alloys or conditions.
Is a galvanized bolt weaker than the same bolt uncoated?
The steel keeps its grade — hot-dip galvanizing per A153/F2329 does not derate the base fastener, and structural bolts are routinely supplied galvanized (only the hardest grades are excluded, for hydrogen-embrittlement risk during processing). The real mechanical consequence is dimensional: the thick zinc requires nuts tapped oversize, so galvanized bolts and nuts must be bought as matched sets.
Do electroplated zinc screws count as galvanized for outdoor use?
No — and the distinction fails fences and decks every year. Electroplating deposits a bright zinc film a small fraction of the hot-dip thickness, adequate indoors and quickly consumed outside, especially against modern treated lumber. When exterior guidance says "galvanized," it means hot-dip galvanized to ASTM A153/F2329, which is dull gray, visibly rough, and marked as such on the carton.
Try the Calculators
Sources
- ASTM A153/A153M and F2329 — zinc coating (hot-dip) on iron and steel hardware and fasteners
- ASTM F593/F594 — stainless steel bolts, screws, studs, and nuts (300-series alloy groups and strength conditions)
- Simpson Strong-Tie published corrosion guidance — fastener/connector selection for preservative-treated wood by chemical and retention, and coastal stainless recommendations
- American Galvanizers Association published data — sacrificial zinc protection mechanism and galvanized-fastener practice (oversize-tapped nuts, embrittlement precautions)