## Common ground
All options are types of lock washers made from different metallic materials.
## Options at a glance
**7318.21 – Iron or steel**
- **Defining trait:** Made from ferrous metal, offering high strength and common use in general mechanical fastening.
- **Typical examples:** Flat spring washers for bolts in automotive or construction.
- **Best fit when:** High load-bearing capacity and cost-effectiveness are priorities.
**7415.21 – Copper**
- **Defining trait:** Conductive, corrosion-resistant, used where electrical continuity is needed.
- **Typical examples:** Washers in electrical connectors or grounding systems.
- **Best fit when:** Electrical conductivity or resistance to oxidation is essential.
**7508.90 – Nickel**
- **Defining trait:** High corrosion and heat resistance; often used in harsh environments.
- **Typical examples:** Aerospace components, chemical equipment.
- **Best fit when:** Exposure to extreme temperatures or corrosive chemicals.
**7616.10 – Aluminium**
- **Defining trait:** Lightweight and corrosion-resistant, but lower strength than steel.
- **Typical examples:** Aircraft parts, consumer electronics.
- **Best fit when:** Weight reduction is critical and loads are moderate.
**7907.00 – Zinc**
- **Defining trait:** Often used as a coating (e.g., galvanized), but also in pure form for sacrificial protection.
- **Typical examples:** Corrosion-resistant washers in outdoor applications.
- **Best fit when:** Protection against rust via sacrificial layer or low-cost corrosion resistance.
**8101.99 – Tungsten**
- **Defining trait:** Extremely high melting point and hardness; used in extreme conditions.
- **Typical examples:** High-temperature industrial fasteners, aerospace.
- **Best fit when:** Exceptional heat or wear resistance is required.
**8102.99 – Molybdenum**
- **Defining trait:** High strength at elevated temperatures; resists creep and oxidation.
- **Typical examples:** Turbine engines, high-temp valves.
- **Best fit when:** Operating in very high-temperature environments.
**8104.90 – Magnesium**
- **Defining trait:** Lightest metal used; prone to corrosion unless protected.
- **Typical examples:** Lightweight structural parts in aerospace.
- **Best fit when:** Weight savings are critical and environment is controlled.
**8108.90 – Titanium**
- **Defining trait:** Excellent strength-to-weight ratio and high corrosion resistance.
- **Typical examples:** Medical implants, aircraft components.
- **Best fit when:** Need for durability, light weight, and resistance to corrosion in demanding settings.
## Key differences
| Material | Strength | Weight | Corrosion Resistance | Heat Resistance | Common Use Case |
|----------------|----------|--------|------------------------|------------------|----------------------------|
| Iron/Steel | High | Medium | Low (unless coated) | Medium | General fastening |
| Copper | Medium | Medium | Medium | Low | Electrical connections |
| Nickel | High | Medium | Very high | High | Harsh environments |
| Aluminium | Medium | Low | High (natural oxide) | Medium | Lightweight applications |
| Zinc | Low | Medium | Moderate (sacrificial) | Low | Outdoor, low-cost protection|
| Tungsten | Very high| Medium | Medium | Very high | Extreme heat |
| Molybdenum | High | Medium | Medium | Very high | High-temp industrial |
| Magnesium | Low | Very low| Low (unless coated) | Low | Lightweight, controlled env|
| Titanium | High | Low | Very high | High | Aerospace, medical |
## How to choose
- Is the washer used in a high-temperature environment? → 8101.99 or 8102.99
- Does weight matter most? → 7616.10 or 8104.90
- Is electrical conductivity needed? → 7415.21
- Is corrosion resistance critical? → 7508.90, 7616.10, or 8108.90
- Is it for general-purpose fastening? → 7318.21
## Overlaps & pitfalls
Some materials (e.g., aluminium, titanium) can be used in similar applications (lightweight, corrosion-resistant), but differ in strength and cost. Tungsten and molybdenum both suit high-temp use but differ in density and availability. No option is clearly superior—choose based on the **main function** of the washer: load, environment, weight, or conductivity