## Common ground
All options are pipe connectors, used to join sections of piping in fluid or gas systems.
## Options at a glance
**3917.40 – Plastic material**
- **Defining trait:** Made from synthetic polymer (e.g., PVC, PP), lightweight and corrosion-resistant.
- **Typical examples:** PVC elbow joints, polypropylene compression fittings.
- **Best fit when:** Used in water supply, drainage, or chemical handling where rust resistance and low cost matter.
**4016.99 – Rubber**
- **Defining trait:** Flexible, elastic material used for seals or flexible couplings.
- **Typical examples:** Rubber hose connectors, expansion joints.
- **Best fit when:** Need vibration damping, flexibility, or sealing in dynamic systems.
**7307 – Iron or steel**
- **Defining trait:** Durable, high-strength metal; often threaded or flanged.
- **Typical examples:** Steel pipe unions, cast iron fittings for heavy-duty pipelines.
- **Best fit when:** High pressure, high temperature, or industrial infrastructure use.
**7412.20 – Copper**
- **Defining trait:** Conductive, corrosion-resistant metal; commonly used in plumbing.
- **Typical examples:** Copper compression fittings, soldered joints in HVAC systems.
- **Best fit when:** Residential plumbing, heating systems, or applications needing thermal conductivity.
**7609.00 – Aluminium**
- **Defining trait:** Lightweight, corrosion-resistant metal; often used where weight is critical.
- **Typical examples:** Aluminum tubing connectors, aerospace or marine fittings.
- **Best fit when:** Applications requiring light weight and resistance to oxidation (e.g., outdoor or mobile systems).
## Key differences
| Feature | Plastic | Rubber | Iron/Steel | Copper | Aluminium |
|------------------|---------------|--------------|---------------|---------------|---------------|
| Weight | Light | Light | Heavy | Medium | Very light |
| Corrosion resistance | High | Moderate | Low (rusts) | High | Very high |
| Pressure tolerance | Medium | Low–Medium | Very high | Medium–High | Medium |
| Thermal conductivity | Low | Very low | High | Very high | High |
## How to choose
- Is the connector made of plastic? → 3917.40
- Does it rely on flexibility or sealing (e.g., rubber hose coupling)? → 4016.99
- Is it used in high-pressure industrial systems or heavy-duty pipelines? → 7307
- Is it for plumbing, HVAC, or where heat transfer matters? → 7412.20
- Is weight a key concern (e.g., mobile or aerospace use)? → 7609.00
## Overlaps & pitfalls
A connector may combine materials (e.g., copper body with rubber seal), fitting both 7412.20 and 4016.99. In such cases, prioritize the **main structural material**. If unclear, use the dominant function: sealing → rubber; heat transfer → copper; strength → steel/iron