Black-Oxide Steel—Typically chosen for their appearance, these nuts have a dark, matte coating to create a finished look. They offer minimal corrosion resistance, so they're best for dry environments.

Hot-Dipped Galvanized Steel—Combines the strength of steel with the rust resistance of stainless steel. These nuts are an economical alternative to 18-8 stainless steel in wet and outdoor environments, but they won't hold up to salt water and chemicals. The galvanized finish is thicker than other types of coatings, so the threads may be more likely to stick during installation. Use with other hot-dipped galvanized fasteners.

Steel—Best for dry environments since moisture will cause these nuts to rust.

Zinc-Flake-Coated Steel—The most durable zinc coating, zinc flake is a multilayer finish that resists wear for long-term rust protection. Similar to zinc yellow-chromate, it won't hold up to harsh chemicals like stainless steel can.