Bearing seals and shields play an important role in protecting the rolling elements, raceways and lubricant inside a bearing. When engineers and buyers select a bearing, they often focus first on dimensions, load capacity and speed. However, the sealing configuration can also influence contamination resistance, grease retention, friction, operating temperature and maintenance requirements.
Three common configurations are open bearings, ZZ shielded bearings and 2RS sealed bearings. Each design has advantages and trade-offs. An open bearing can provide very low rotational resistance and easy lubrication access, while a shielded or sealed bearing can provide progressively stronger protection against external contamination. The best choice depends on the application rather than on a simple rule that “more sealing is always better.”
1. Why Do Bearings Need Seals or Shields?
Inside a rolling bearing are the inner and outer raceways, rolling elements, cage and lubricant. These components must remain in suitable working condition if the bearing is to rotate smoothly and reliably.
In dusty, humid or contaminated environments, foreign particles can enter the bearing and mix with the lubricant. Hard particles may behave like abrasives and accelerate wear on the raceways and rolling elements. Moisture can also contribute to corrosion, while lubricant loss or degradation can increase friction and operating temperature.
A suitable sealing or shielding arrangement can therefore help reduce contamination, retain grease and reduce maintenance. At the same time, every additional sealing feature can influence friction and heat generation. For that reason, the sealing method should be matched to the actual operating environment, speed and maintenance strategy.
2. Open vs ZZ vs 2RS Bearings: Key Differences
| Bearing Type | Construction | Main Characteristics | Typical Applications |
| Open Bearing | No shields or integrated contact seals | Low friction; easy lubrication access; limited contamination protection | Clean environments; externally lubricated or regularly maintained machinery |
| ZZ / 2Z Bearing | Metal shields on both sides | Relatively low sealing friction; helps block larger particles and retain grease | Electric motors, automation equipment, fans and general machinery |
| 2RS Bearing | Elastomer/rubber seals on both sides | Stronger protection against dust, moisture and grease loss; typically higher seal friction | Dusty, humid, outdoor or low-maintenance applications |
Related product category: Deep Groove Ball Bearings
Note: bearing suffix conventions can vary by manufacturer. “ZZ” and “2Z” are commonly used for double metal shields, while “2RS” generally indicates seals on both sides. Always confirm the exact manufacturer specification when interchangeability matters.
3. When Should You Use Open Bearings?
Open bearings have no built-in shields or seals covering the rolling elements. Because there is no additional sealing contact, they can offer low rotational resistance and allow lubricant to be added, circulated or replaced easily.
They are commonly considered when the surrounding equipment already protects the bearing from contamination, or when the machine uses an external lubrication system. They can also be useful where low friction, heat dissipation or frequent inspection is more important than integrated contamination protection.
- The operating environment is clean.
- External lubrication is available.
- Regular inspection and maintenance are practical.
- The bearing is enclosed by a separate housing or machine structure.
- Low rotational resistance is a priority.
Open bearings are generally less suitable for exposed environments containing dust, moisture, washdown spray or other contaminants unless the machine provides separate sealing around the bearing position.
4. What Are ZZ Shielded Bearings?
ZZ bearings use metal shields on both sides. The shields are positioned close to the rotating ring and normally create little or no rubbing contact compared with a contact rubber seal. This helps keep rotational resistance relatively low while still providing a basic barrier against larger particles and helping retain grease.
For this reason, ZZ bearings are widely used where the environment is reasonably clean but the bearing still needs some protection. Typical examples include electric motors, fans, automation equipment, compact mechanisms and general industrial machinery.
- Relatively low sealing friction
- Good grease retention for many general applications
- Basic protection against larger dust particles
- Suitable for many moderate- to high-speed applications when the bearing design and lubricant are appropriate
For small motors and compact mechanisms, see also: Miniature Ball Bearings
A limitation of metal shields is that they do not normally provide the same protection against fine dust, moisture or liquid contamination as a well-designed rubber seal.
5. What Are 2RS Sealed Bearings?
2RS bearings use elastomer or rubber seals on both sides of the bearing. Depending on the specific design, the seal may contact or run very close to the bearing ring. This creates a stronger barrier against contamination and helps keep grease inside the bearing.
Compared with ZZ shielded bearings, 2RS bearings are often preferred in dusty, humid or exposed environments, especially where maintenance access is limited. They are commonly used in outdoor machinery, material-handling equipment, certain vehicle components, agricultural equipment and many other applications where contamination protection is important.
- Improved protection against dust and fine contaminants
- Better resistance to moisture ingress than a typical metal shield
- Improved grease retention
- Reduced need for frequent relubrication in many sealed-for-life designs
The trade-off is friction. Contact seals can increase running torque and heat compared with an open or shielded bearing. For high-speed applications, the effect of seal design on temperature and speed capability should therefore be evaluated rather than assumed.
The RMO Manufacturing Advantage: RMO bearings are manufactured from high-quality GCr15 bearing steel using martensitic oil quenching and low-temperature tempering, with hardness controlled at HRC 60–63 for wear resistance and rolling-contact durability. Each bearing passes through more than 100 manufacturing and inspection processes, covering material preparation, heat treatment, precision grinding, assembly and final inspection.
Our sealed bearings can use a precision-machined V-groove seal seat on the inner ring together with reinforced triple-lip NBR seals to improve protection against dust, moisture and grease leakage. For higher-temperature or chemically demanding applications, FKM seal options are also available.
According to operating requirements, RMO can select low-noise bearing greases and optimize grease fill quantity to balance sealing performance, running torque, noise and temperature rise. Selected grease options can cover operating ranges of approximately -20°C to 160°C, depending on the specific lubricant and bearing configuration.
6. ZZ vs 2RS Bearings: Which Should You Choose?
| Operating Condition | Typical Direction |
| Clean environment | Open or ZZ |
| General industrial dust | ZZ or 2RS depending on contamination level |
| Moisture or splash exposure | 2RS, subject to the exact seal design |
| Dusty or dirty environment | 2RS |
| Very low-friction requirement | Open or ZZ |
| Limited maintenance access | 2RS |
| External oil or grease circulation | Open |
| High-speed operation | Evaluate speed rating, lubricant, seal friction and temperature together |
The final choice should not be based on the suffix alone. Bearing size, speed, temperature, lubricant, contamination level and maintenance requirements should all be considered together.
7. Is a More Tightly Sealed Bearing Always Better?
No. Stronger sealing can improve contamination protection, but it can also increase friction. A bearing running at high speed inside a clean enclosed machine does not necessarily need the same sealing arrangement as a bearing mounted on outdoor equipment exposed to dust and moisture.
The goal is to use enough protection for the environment without introducing unnecessary friction, heat or cost. In practice, this often means balancing contamination risk against speed and torque requirements.
A useful rule of thumb: choose the sealing level that adequately protects the bearing without creating unnecessary resistance for the application.
8. Speed, Temperature, Lubrication and Material Also Matter
Seal selection is only one part of bearing selection. A 2RS bearing operating at moderate speed in a dusty environment may be a good solution, while the same sealing design may be unsuitable for an application with very high rotational speed or elevated temperature.
Lubricant type and fill quantity also affect torque and temperature. In addition, the bearing material and seal material must be compatible with the working environment. Where corrosion, chemicals or unusual temperatures are present, it may be necessary to evaluate stainless steel, ceramic, special grease or a different seal compound rather than relying only on a standard suffix.
The same principle applies to low-temperature or elevated-temperature service. Seal flexibility, grease viscosity and internal clearance can change with temperature, so the suffix by itself does not define the complete operating capability of the bearing.
For equipment exposed to frequent washdown, aggressive cleaning agents or chemical vapors, a standard 2RS configuration may still be insufficient. The complete bearing system should be reviewed, including ring material, seal compound, lubricant compatibility and surrounding housing protection. In these cases, the correct solution may involve stainless steel, a special elastomer, a different grease or an external seal in addition to the bearing’s own seals.
9. What Information Should Buyers Provide?
For an OEM or industrial bearing project, providing the following information can help determine whether an open, shielded or sealed configuration is more appropriate:
- Bearing model or dimensions
- Rotational speed
- Radial and axial load
- Operating temperature
- Dust or contamination level
- Moisture or splash exposure
- Lubrication method
- Required service life
- Installation environment
- Required quantity
For unusual operating conditions, a drawing, sample or equipment description can help confirm the most suitable bearing construction.
10. Open, ZZ or 2RS: Final Selection Guide
Choose Open bearings when low friction, external lubrication and a clean or separately sealed environment are priorities.
Choose ZZ bearings when relatively low friction is required together with basic dust protection and grease retention.
Choose 2RS bearings when stronger protection against dust, moisture and contamination is needed and slightly higher sealing friction is acceptable.
Browse related products: Ball Bearings
Frequently Asked Questions
What does ZZ mean on a bearing?
ZZ commonly indicates metal shields on both sides of the bearing. Some manufacturers use the designation 2Z for the same general configuration. Always confirm the supplier’s specification when replacing an existing bearing.
What does 2RS mean on a bearing?
2RS generally indicates seals on both sides of the bearing. The exact seal material and contact design can vary, so speed, temperature and environmental limits should be checked for the specific bearing.
Is 2RS waterproof?
A 2RS bearing normally provides stronger protection against moisture and contamination than an open or shielded bearing, but it should not automatically be treated as fully waterproof. Protection depends on seal design, fit, pressure, exposure and operating conditions.
Can I replace ZZ with 2RS?
Sometimes the dimensions are interchangeable, but friction, speed capability, temperature and lubrication requirements may change. The application should be checked before changing the sealing type.
Need Help Choosing Between Open, ZZ and 2RS Bearings?
Still Unsure Which Seal Fits Your Application? Let Our Engineers Review It.
Choosing the wrong seal can increase friction, allow contamination to enter, or shorten bearing service life.
Send RMO Bearings your operating conditions — including speed, temperature, contamination level, bearing size and required quantity — and our technical team will review the application and recommend a suitable sealing configuration.
Qualified OEM projects can also request sample testing before bulk production.