## Common ground
All options are types of washers and seals categorized by their primary material.
## Options at a glance
**3926.90 – Plastic**
- **Defining trait:** Made from synthetic polymer materials like polyethylene or PTFE.
- **Typical examples:** Nitrile rubber gaskets, plastic O-rings, PVC washers.
- **Best fit when:** Used in low-to-medium temperature environments, corrosion resistance needed, or for non-metallic applications.
**4006.90,4016.93 – Rubber**
- **Defining trait:** Made from natural or synthetic elastomers (e.g., EPDM, neoprene).
- **Typical examples:** Car engine seals, rubber gaskets, hose washers.
- **Best fit when:** Flexibility, shock absorption, and sealing under pressure are critical.
**4205.00 – Leather/Composition leather**
- **Defining trait:** Made from animal hide or synthetic leather-like materials.
- **Typical examples:** Leather washers in vintage machinery, composition leather seals.
- **Best fit when:** Traditional or decorative use; low-pressure sealing in older equipment.
**4823.90 – Paper/Paperboard**
- **Defining trait:** Made from compressed or treated paper materials.
- **Typical examples:** Kraft paper washers, cardboard gaskets.
- **Best fit when:** Low-cost, disposable, or low-load applications (e.g., packaging).
**6814.10 – Mica**
- **Defining trait:** Made from naturally occurring mineral mica, known for heat and electrical insulation.
- **Typical examples:** High-temperature electrical insulating washers, thermal seals.
- **Best fit when:** Electrical or thermal insulation in high-temp environments.
**7318.21,7318.22 – Iron/Steel**
- **Defining trait:** Made from ferrous metals; often hardened or plated.
- **Typical examples:** Steel washers in heavy machinery, bolted joints under load.
- **Best fit when:** High strength, durability, and resistance to wear are required.
**7415.21 – Copper**
- **Defining trait:** Made from pure copper; excellent thermal/electrical conductivity.
- **Typical examples:** Copper gaskets in plumbing, electrical connectors.
- **Best fit when:** Conductivity or corrosion resistance in wet environments is key.
**8108.90 – Titanium**
- **Defining trait:** Made from lightweight, high-strength, corrosion-resistant metal.
- **Typical examples:** Aerospace seals, marine hardware washers.
- **Best fit when:** Extreme durability, light weight, and resistance to harsh environments (e.g., saltwater).
## Key differences
| Material | Flexibility | Corrosion Resistance | Thermal Conductivity | Strength | Typical Use Case |
|--------------|-------------|------------------------|------------------------|----------|----------------------------|
| Plastic | High | Medium | Low | Low | General-purpose, low temp |
| Rubber | Very High | Medium (varies) | Low | Medium | Dynamic sealing |
| Leather | Medium | Low | Low | Low | Vintage or decorative |
| Paperboard | Low | Very Low | Low | Very Low | Disposable, low load |
| Mica | Low | High | Low | Medium | Electrical/thermal insulation |
| Iron/Steel | Low | Low (unless coated) | Medium | High | Heavy-duty mechanical |
| Copper | Medium | Medium (oxidizes) | Very High | Medium | Plumbing, electrical |
| Titanium | Medium | Very High | Medium | Very High| Aerospace, marine |
## How to choose
- Is the product used in high heat or electrical applications? → 6814.10 (Mica)
- Does it need to conduct electricity or heat? → 7415.21 (Copper)
- Is it for heavy machinery or high load? → 7318.21,7318.22 (Iron/Steel)
- Is it in a corrosive environment (e.g., seawater)? → 8108.90 (Titanium)
- Is it flexible and used under pressure? → 4006.90,4016.93 (Rubber)
## Overlaps & pitfalls
- A copper washer may also be used in high-temp settings—could fit both 7415.21 and 6814.10, but priority should go to **main function**: conductivity vs. insulation.
- Plastic washers can mimic rubber in flexibility—choose based on material type (plastic vs. elastomer).
- Leather and paperboard are easily confused; leather is durable and flexible, paperboard is thin and disposable.
- No option clearly defines "composite" materials—use the **primary material** as the deciding factor