Technical Guide · 4 min read
Bearing Seal Types Explained: Open, 2Z, 2RS, 2RZ
Open, 2Z, 2RS, 2RZ — what each seal type means, when to use it, and how it affects speed and temperature limits.
Why Seals Matter
The seal or shield on a bearing serves two purposes: keeping contaminants out and keeping lubricant in. The type of seal directly affects the bearing's maximum speed, operating temperature, friction, and service life.
Choosing the wrong seal type is one of the most common causes of premature bearing failure. An open bearing in a dusty environment will fail quickly from contamination. A contact-sealed bearing in a high-speed application will overheat from friction.
Open Bearings (No Suffix)
An open bearing has no seals or shields. It offers the lowest friction and highest speed capability, but provides no protection against contamination.
Use when:
The bearing is in a sealed housing that provides external protection
Maximum speed is needed (the bearing itself is the least restrictive element)
You're using an external lubrication system (oil bath, mist, or jet)
Avoid when:
Dust, moisture, or particles are present
The bearing must retain its own grease
Metal Shields (2Z / ZZ)
Metal shields are thin steel plates attached to the outer ring with a small gap to the inner ring. They're "non-contact" — the shield doesn't touch the rotating inner ring.
Characteristics:
Lower friction than rubber seals
Higher speed capability (90–95% of open bearing speed)
Moderate contamination protection (blocks large particles, not fine dust)
Temperature range: −30°C to +110°C (standard)
Use when:
Moderate contamination is expected
Speed is important
The environment is relatively dry
Rubber Contact Seals (2RS / DDU / LLU)
Rubber seals (typically nitrile or FKM/Viton) press against the inner ring, creating a contact seal. This provides the best contamination protection but adds friction.
Characteristics:
Highest contamination protection (dust, moisture, splash water)
Lower speed capability (70–80% of open bearing speed)
More friction and heat generation than shields
Standard nitrile: −30°C to +110°C; Viton: −20°C to +200°C
Use when:
Dust, moisture, or washdown conditions exist
The bearing must retain grease for its entire service life
Relubrication is not possible or practical
Non-Contact Seals (2RZ)
Non-contact rubber seals combine the sealing benefit of rubber with the low friction of shields. The rubber lip has a small gap to the inner ring instead of making contact.
Characteristics:
Better contamination protection than metal shields
Lower friction than contact seals
Speed capability: 85–90% of open bearing speed
Good compromise for moderate environments
Use when:
You need better sealing than shields but can't accept the friction of contact seals
Medium-speed applications with some contamination risk
Selection Summary
| Seal Type | Speed | Protection | Friction | Best For |
|---|---|---|---|---|
| Open | Highest | None | Lowest | Sealed housings, oil lubrication |
| 2Z (Shield) | High | Moderate | Low | Dry, moderate environments |
| 2RZ (Non-contact) | Medium-High | Good | Medium | Balanced applications |
| 2RS (Contact seal) | Medium | Best | Higher | Dusty, wet, maintenance-free |