Protective coatings for industrial fasteners
A quick comparison of the most common protective coatings used for industrial fasteners, based on corrosion resistance, application and technical characteristics.nt.
How to choose the right coating
The selection of a protective coating is not based only on corrosion resistance.
Friction behavior, assembly requirements and compliance with specifications are often equally critical.
Typical selection logic:
Indoor / low exposure → Zinc plating
Automotive / controlled tightening → Zinc flake + topcoat
Outdoor / structural → Hot dip galvanizing
Aesthetic / low protection → Black oxide
| Surface Treatment | White Rust (hrs) | Red Rust (hrs) | Friction Control | Hydrogen Embrittlement | Application Limits | Notes |
|---|---|---|---|---|---|---|
| Zinc Plating (Clear) | 24–72 | 120–240 | No | Risk (≥10.9) | No | Requires dehydrogenation for high strength fasteners. |
| Zinc Plating (Yellow) | 72–120 | 200–400 | No | Risk (≥10.9) | No | Improved corrosion resistance compared to clear zinc. Dehydrogenation required for high strength fasteners. |
| Zinc-Nickel | 120–240 | 500–1000+ | Optional | Low | No | High corrosion resistance, commonly used for automotive applications. |
| GEOMET® 321 (Basecoat) | — | 600–800 | No | No | No | Standard zinc flake coating. No hydrogen embrittlement risk. |
| GEOMET® 321 + Topcoat | — | 720–1000+ | Yes | No | No | Controlled friction system. Typical friction range: 0.06–0.18 depending on topcoat. |
| GEOMET® 500 | >240 without white rust | 720–1000+ | Yes | No | No | Integrated lubricant. Typical friction coefficient: 0.15 ± 0.03. |
| GEOMET® + Topcoat (PLUS®, GEOKOTE®) | — | 1000–1500+ | Yes | No | No | High-performance zinc flake systems with improved friction control and corrosion resistance. |
| GEOBLACK® | — | Up to 1000 | Yes | No | No | Black zinc flake system combining corrosion protection with aesthetic appearance. |
| Hot Dip Galvanized | — | 500–1500+ | No | No | Yes | Not recommended for small diameters or fine threads due to coating thickness and thread fit issues. |
| Phosphated (Oiled) | — | 24–96 | No | No | No | Temporary protection, typically used as a base or for indoor applications. |
| Black Oxide (Oiled) | — | 24–72 | No | No | No | Minimal corrosion resistance, mainly chosen for appearance or light indoor use. |
Salt spray test values are indicative and may vary depending on coating thickness, process parameters and part geometry.
Friction values may vary depending on lubrication systems and assembly conditions.
Electroplated zinc coatings may introduce hydrogen into the material. For high strength fasteners (≥ 10.9), a controlled dehydrogenation process after plating is required to reduce the risk of brittle failure.