## Common ground
All options are fasteners used to secure mechanical joints, specifically cotter pins or cotters made from different metals.
## Options at a glance
**7318.24 – Iron/Steel**
- **Defining trait:** Highest strength and durability; most commonly used for heavy-duty applications.
- **Typical examples:** Shaft couplings, valve assemblies, industrial machinery.
- **Best fit when:** High load-bearing or high-stress environments are expected.
**7415.33 – Copper**
- **Defining trait:** Corrosion resistance and electrical conductivity; non-magnetic.
- **Typical examples:** Electrical connectors, marine hardware, low-friction joints.
- **Best fit when:** Corrosive environments or where magnetism must be avoided.
**7508.90 – Nickel**
- **Defining trait:** Excellent heat and corrosion resistance; used in extreme conditions.
- **Typical examples:** Aerospace components, high-temp engines, chemical equipment.
- **Best fit when:** High temperature or aggressive chemical exposure.
**7616.10 – Aluminium**
- **Defining trait:** Lightweight with moderate strength; resists corrosion.
- **Typical examples:** Aircraft parts, automotive trim, consumer electronics.
- **Best fit when:** Weight reduction is critical and loads are light to moderate.
**7907.00 – Zinc**
- **Defining trait:** Low cost and good machinability; prone to corrosion unless coated.
- **Typical examples:** Low-cost fasteners, temporary assemblies, toys.
- **Best fit when:** Budget constraints and short-term use.
**8101.99 – Tungsten**
- **Defining trait:** Exceptional hardness and high melting point; very dense.
- **Typical examples:** High-wear applications, cutting tools (rare for cotter pins).
- **Best fit when:** Extreme wear resistance needed (uncommon for standard cotter pins).
**8102.99 – Molybdenum**
- **Defining trait:** High-temperature stability and strength; used in extreme environments.
- **Typical examples:** Rocket engines, furnace components.
- **Best fit when:** Very high temperatures (>1000°C) are involved.
**8104.90 – Magnesium**
- **Defining trait:** Lightest metal; highly flammable and prone to corrosion.
- **Typical examples:** Aerospace models, experimental devices.
- **Best fit when:** Weight savings outweigh safety risks (rare).
**8108.90 – Titanium**
- **Defining trait:** High strength-to-weight ratio and excellent corrosion resistance.
- **Typical examples:** Aircraft, medical implants, marine hardware.
- **Best fit when:** Need for lightweight, strong, and durable fasteners.
## Key differences
| Metal | Strength | Weight | Corrosion Resistance | Temperature Use |
|-------------|----------|---------|------------------------|------------------|
| Iron/Steel | Very High| Medium | Low (unless coated) | Moderate |
| Copper | Low | Medium | High | Low-Moderate |
| Nickel | High | Medium | Very High | Very High |
| Aluminium | Medium | Low | High | Moderate |
| Zinc | Low | Medium | Low | Low |
| Tungsten | Extreme | Very High| Medium | Extremely High |
| Molybdenum | High | Medium | High | Extremely High |
| Magnesium | Low | Very Low| Low | Low |
| Titanium | High | Low | Very High | Moderate-High |
## How to choose
- Is strength the top priority? → 7318.24 (Steel)
- Is weight critical? → 7616.10 (Aluminium) or 8108.90 (Titanium)
- Is corrosion a concern? → 7415.33 (Copper), 7508.90 (Nickel), or 8108.90 (Titanium)
- Is temperature extreme? → 7508.90 (Nickel) or 8102.99 (Molybdenum)
## Overlaps & pitfalls
- Some metals (e.g., titanium, nickel) suit both high strength and corrosion resistance.
- Tungsten and molybdenum are rarely used for standard cotter pins—may indicate specialized or non-standard use.
- If the product is not intended for extreme conditions, avoid exotic metals unless required.
- **No priority rule given**—choose based on the product’s MAIN function: strength, weight, corrosion resistance, or temperature