When a screw is exposed to moisture and oxygen, it may undergo oxidation, thus corroding. How exactly does zinc protect screws from corrosion? Well, zinc can still corrode, but it corrodes at a significantly slower rate than other metals and alloys.

Are zinc plated screws OK for outdoor use?

We do not recommend electro-galvanized screws (also called clear-zinc coated) for exterior applications. They will corrode quickly in contact with the elements. Mechanically galvanized screws are generally suitable for decks and other outdoor projects made of pressure-treated lumber.

Do zinc plated screws resist rust?

Typically, there are a couple of choices in plated woodscrews: brass or zinc, with zinc being the most common. Either one of these plated screws provides adequate rust protection -- if they're used on indoor project. ... On top of this is a thin coat of a clear, rust-resistant material, almost like a see-through raincoat.