Bolt surface treatments are essential for maximizing durability, preventing corrosion, and ensuring performance in harsh environments. For military, aerospace, and industrial applications, selecting the right coating or finish can mean the difference between mission success and unexpected failure.
1. Common Coatings & Their Benefits
- Zinc Plating & Hot-Dip Galvanizing
Provides cathodic protection via sacrificial corrosion. Zinc plating is lighter but less durable than hot-dip galvanizing. Great for general outdoor conditions. - Zinc-Nickel Plating
Offers superior salt-spray resistance and is often cadmium-free, making it safer for aerospace or defense use. This eco-friendly alternative resists hydrogen embrittlement and meets ISO 10683 guidelines. - Zinc Flake Coatings
Non-electrolytic coating that avoids hydrogen embrittlement. Provides corrosion protection from 240 to over 1,500 hours salt spray per ISO and EN specs. Ideal for high-strength fasteners. - Cadmium Plating
Features sacrificial protection and high lubricity. Historically used in aerospace, especially for legacy systems. Though highly effective, its toxicity limits modern use.
2. Specialty Treatments & Conversion Coatings
- Electroless Nickel Plating
Uniform, wear-resistant, and corrosion-protective, this is ideal for precision fasteners, sensors, or vacuum environments. - Electro Nickel Plating
Provides decorative shine, corrosion resistance, and conductivity. Excellent for high-load or exposed hardware. - Black Oxide Coating
Conversion coating for steel and stainless components. Adds minimal thickness while offering basic corrosion resistance; often combined with oil or wax impregnation. - Chromate Conversion Coating (Alodine)
Passivates aluminum and zinc surfaces, improves paint and adhesive adhesion, and maintains conductivity. Typical in aerospace and electronic systems. - Chrome Plating (Hard Chrome)
Delivers extreme surface hardness and excellent corrosion resistance. Used in high-wear or high-pressure fasteners—but costly and regulated for toxicity.
Bolt Coating Comparison Table
| Finish Type | Key Advantages | Military & Industrial Applications |
|---|---|---|
| Zinc or Hot-Dip Galvanizing | Economic cathodic protection | General structural bolts, outdoor gear |
| Zinc‑Nickel Plating | High corrosion resistance; cadmium-free | Ground vehicles, avionics systems |
| Zinc Flake Coating | Hydrogen embrittlement-free; 1 000+ hrs salt spray | High-strength grade 10.9/12.9 bolts |
| Electroless Nickel | Uniform wear resistance & corrosion protection | Precision fasteners, vacuum environments |
| Black Oxide | Minimal dimensional impact; low corrosion if oiled | Interior hardware, mil‑spec connectors |
| Chromate Conversion (Alodine) | Passivation; adhesion for paint/adhesives | Aluminum alloy parts, electronics mounts |
| Hard Chrome Plating | Exceptional hardness; wear and abrasion resistance | High-wear military couplings, hydraulic components |
3. Why Finish Selection Matters
- Performance Under Stress
Corrosion-resistant coatings prevent joint failure under salt, chemicals, and temperature cycles. - Material Compatibility
Avoid hydrogen embrittlement by using non-electrolytic coatings like zinc flake for high-strength or heat-treated steels. - Traceability & Compliance
Military applications require documented finishes that meet MIL-SPEC or ISO standards to support procurement audits and lifecycle traceability. - Dimensional Precision
Finishes like zinc flake and black oxide maintain tight tolerances—critical in threaded and precision assemblies
Partner with Metric Bolt for Certified Coated Fasteners
At Metric Bolt, we deliver fasteners pre-treated with certified finishes—zinc-nickel, zinc flake, cadmium, electroless nickel, black oxide, and chromate conversion. All are compliant with MIL-SPEC / DFAR requirements and backed by traceable documentation, salt-fog testing data, and material certificates.
Need mission-grade coated fasteners with detailed certification?
Contact Metric Bolt for expert consultation, procurement support, or finish selection guidance.
