WTFastenersZinc vs Hot-Dip Galvanized vs Dacromet: Which Coating for Outdoor Fasteners?
Two identical bolts can have service lives that differ by a factor of ten — the difference is the coating. Here is how zinc, hot-dip galvanizing and Dacromet compare, and how to pick the right one.
Zinc plating: the everyday indoor finish
Zinc plating (electro-zinc) is the default finish on catalog fasteners for good reason: it is economical, gives a clean bright appearance, takes paint well, and protects indoor and sheltered steel adequately. The zinc layer is thin — measured in microns — so it suits dry interiors, covered structures and assemblies that stay out of standing water. It is the right answer when the fastener lives indoors; it is the wrong answer on a seaside roof.
Hot-dip galvanizing: the heavy outdoor armor
Hot-dip galvanizing is the heavy-duty outdoor answer. The fastener is dipped in molten zinc, building a thick, metallurgically bonded coating — an order of magnitude thicker than electro-zinc — that protects even scratched areas through the zinc's sacrificial behavior. That is why structural bolts, anchors and outdoor steelwork are routinely specified hot-dip galvanized: bridges, transmission towers, solar mounting, fencing and coastal structures. The trade-off is dimensional: the thick coating adds measurable thickness, so hot-dip galvanized nuts are tapped oversize to fit — order bolt and nut as a matched set, which the catalog does.
Dacromet: thin film, serious corrosion resistance
Dacromet is a different technology: a thin inorganic coating of zinc and aluminum flakes in a chromate binder, baked onto the fastener. Despite being only a few microns thick, it delivers corrosion resistance that rivals or exceeds hot-dip galvanizing in salt-spray testing, with no dimensional change — threads stay as-made, which matters for precision assemblies. Because there is no acid pickling and no molten zinc bath, it also avoids the hydrogen embrittlement risk that plagues high-strength electroplated fasteners. It is the choice when you need outdoor-grade protection on tight-tolerance or high-strength parts.
Galvanized (G.I.), Ruspert and black oxide in brief
The remaining catalog finishes fill the gaps. Galvanized (G.I.) — lighter zinc coatings — sits between electro-zinc and hot-dip for sheltered-outdoor use. Ruspert is a baked ceramic-metallic coating system popular in roofing and cladding screws for its combination of corrosion resistance and consistent torque behavior. Black oxide is a thin conversion coating that gives a clean black appearance with minimal dimensional change, but it offers only mild corrosion protection on its own and is usually oiled or waxed — best for indoor, oil-friendly assemblies rather than weather exposure.
Matching the coating to the exposure
The selection rule is simple: match the coating to the worst exposure the fastener will see over its life, not the average. Indoor and dry: zinc plating. Outdoor structural and anchors: hot-dip galvanizing. Outdoor with tight tolerances or high strength: Dacromet. Roofing and cladding screws: Ruspert or galvanized finishes with EPDM sealing washers. When the environment is coastal, agricultural or industrial, step one grade heavier than the minimum — the coating is the cheapest line on the order and the most expensive thing to replace in the field.
Every finish above is a catalog option at WTFasteners (Hebei W.T Fasteners Co., Ltd.), a source factory in Yongnian, Handan, China. State the exposure conditions with the inquiry — WhatsApp +86 138 0310 6448 or postmaster@wtfastener.com — and the coating is confirmed factory-direct against the application. Browse the finishes across the self-drilling screws and anchors ranges.
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