Open vs ZZ vs 2RS Deep Groove Ball Bearings Explained

The Direct Answer: Which Suffix Should You Choose?

When selecting a deep groove ball bearing, the suffix after the bearing number — Open, ZZ, or 2RS — defines the sealing arrangement and determines suitability for your application. Here is the short answer:

• Open bearings have no shields or seals. Choose them when external lubrication is supplied continuously and operating speeds are very high.
• ZZ (metal-shielded) bearings are grease-packed and shielded on both sides with thin steel plates. Choose them for moderate-speed, dry, or lightly contaminated environments where occasional re-lubrication is possible.
• 2RS (rubber-sealed) bearings are grease-packed and sealed on both sides with contact rubber seals. Choose them for wet, dusty, or heavily contaminated environments where sealed-for-life performance is required.

In practice, 2RS is the most widely specified variant across general engineering, automotive, and industrial applications because it provides the best contamination exclusion with acceptable speed capability. ZZ suits higher-speed dry machinery, and Open suits precision or high-speed applications where lubrication is externally managed.

What Deep Groove Ball Bearings Are and Why the Suffix Matters

Deep groove ball bearings (DGBBs) are the most commonly used bearing type in the world, accounting for roughly 80% of all ball bearing applications globally. They are designed to support radial loads and moderate axial loads in both directions, and are available across a wide bore range — typically from 3 mm (miniature series) to over 400 mm in large industrial sizes.

The core geometry — deep raceway grooves that closely conform to the balls — is identical across Open, ZZ, and 2RS variants of the same bearing number. What changes is the protection arrangement at the sides of the bearing. This distinction affects grease retention, contamination exclusion, friction torque, maximum speed, and maintenance interval. A misjudged suffix can cause premature failure within weeks; the correct choice can deliver the full rated L10 bearing life — often 20,000 to 100,000+ operating hours in properly applied conditions.

Suffix conventions vary slightly by manufacturer. The most common equivalencies are:

• ZZ (SKF, NSK, NTN) = 2Z (FAG/Schaeffler) = metal shields both sides
• 2RS (NSK, NTN) = 2RSH (SKF) = 2RSR (FAG) = rubber contact seals both sides
• Open = no suffix, or sometimes designated with a blank suffix in catalogue tables

Open Bearings: Maximum Speed, No Built-In Protection

An open deep groove ball bearing has no shields or seals on either side. The raceways and balls are fully exposed. This is not a fault — it is a deliberate design choice suited to specific operating conditions.

How Open Bearings Are Lubricated

Open bearings are either supplied dry (for the user to pack with grease or oil during assembly) or lubricated by an external oil circulation or mist lubrication system in the machine. In high-speed spindle applications, oil-air lubrication is injected directly into the bearing from outside — a method that requires the bearing to be open so oil can flow through and carry away heat.

Speed Advantage of Open Bearings

Because there is no contact friction from seals and no churning resistance from pre-packed grease, open bearings can operate at the highest speeds of the three variants. For a typical 6206 bearing (30 mm bore), the SKF reference speed for an open version is approximately 14,000 rpm, compared to 12,000 rpm for 2Z (ZZ) and 9,000 rpm for 2RSH (2RS).

Where Open Bearings Are Used

• CNC machine tool spindles and grinding wheel spindles where high-speed precision is critical.
• Gearbox internals bathed in oil — the bearing sits in an oil sump and lubrication is constant.
• Electric motors in clean environments where the motor's own grease nipples feed the bearing externally.
• Applications where the bearing requires periodic cleaning and re-packing as part of a planned maintenance schedule.

Limitations of Open Bearings

• Zero contamination protection — dust, water, and debris enter freely and directly abrade the raceways.
• Grease is not retained — in grease-lubricated applications, open bearings require more frequent re-greasing intervals.
• Not suitable for outdoor, wet, dusty, or food-processing environments without additional housing seals.

ZZ Bearings: Metal Shields for Moderate Protection at High Speed

ZZ bearings are fitted with two thin pressed-steel shields, one on each side of the bearing. These shields are fixed to the outer ring and have a small running clearance from the inner ring — they do not make contact. This non-contact arrangement is central to the ZZ bearing's behaviour.

How ZZ Shields Work

Because the steel shield does not touch the inner ring, there is zero additional friction torque from the shielding itself. The shield acts as a labyrinth: it creates a narrow gap (typically 0.1–0.3 mm) that restricts the ingress of large particles and retains grease by reducing centrifugal throw-out. However, this gap is not sealed — fine dust, water vapour, and liquid can still penetrate given sufficient pressure or prolonged exposure.

ZZ bearings are supplied pre-greased at the factory, typically filled to 25–35% of the free internal volume with a lithium-complex or polyurea grease. Because the grease is enclosed on both sides, re-lubrication from outside is not possible without disassembly — making grease selection at the point of manufacture critical.

Speed and Temperature Capability

The non-contact shield generates no frictional heat, so ZZ bearings run cooler than 2RS bearings at equivalent speeds. For the same 6206 bearing, a typical ZZ variant achieves a thermal speed rating approximately 15–25% higher than the 2RS equivalent. Operating temperature limits are generally governed by the grease specification rather than the shield material — standard grades run to approximately 120°C continuous, with high-temperature greases extending this to 150°C or beyond.

Typical ZZ Bearing Applications

• Electric motors in dry, clean indoor environments — one of the highest-volume applications globally.
• Fans, blowers, and ventilation equipment where airborne dust is present but moisture ingress is minimal.
• Household appliances: washing machine drums, vacuum cleaner motors, power tools.
• Automotive alternators and idler pulleys — higher-speed, dry-environment applications.
• Conveyor systems in dry warehouses and light manufacturing.

Limitations of ZZ Bearings

• The non-contact gap allows fine contamination (particles below ~0.2 mm) and moisture to enter over time — unsuitable for wash-down environments.
• The steel shield can corrode in humid or chemically aggressive environments, potentially introducing metallic debris into the raceway.
• Grease cannot be replenished without bearing removal — the pre-packed grease must be matched to the application's expected service life.

2RS Bearings: Rubber Contact Seals for Maximum Contamination Exclusion

2RS bearings are fitted with two rubber contact seals, one on each side. The seal lip — made from nitrile rubber (NBR) in standard variants, or HNBR, EPDM, or PTFE-lipped versions for demanding environments — makes a continuous rubbing contact with a groove in the inner ring. This contact creates a genuine barrier against contamination and lubricant loss.

Why 2RS Provides Superior Sealing

Unlike the ZZ shield's labyrinth gap, the 2RS seal lip physically closes the path between the bearing's interior and the outside environment. This means fine dust, water spray, process fluids, and abrasive particles cannot enter the bearing cavity under normal operating conditions. Independent testing has shown that 2RS bearings in contaminated environments achieve 3 to 10 times the service life of equivalent ZZ bearings — the exact multiple depending on contamination severity and speed.

The grease fill level in 2RS bearings is also typically higher — up to 30–40% of free internal volume — as the sealed environment minimises grease oxidation and moisture contamination, maintaining lubrication film integrity throughout the bearing's life.

The Speed Penalty of Contact Seals

The rubber lip in contact with the inner ring generates additional friction torque. At low to moderate speeds this is negligible, but at high rotational speeds the frictional heat generated can raise bearing temperature and accelerate grease degradation. The contact seal also imposes a lower limiting speed compared to ZZ or Open variants. For a 6206 2RS bearing, the reference speed is typically around 9,000 rpm versus 12,000 rpm for the ZZ equivalent and 14,000 rpm for Open.

Some manufacturers offer a low-friction variant — designated 2RSL (SKF) or 2RZ — in which the seal lip has been optimised to reduce contact force while retaining the sealing function. These variants partially close the gap between 2RS and ZZ speed capability while maintaining much better contamination exclusion than a shield.

Typical 2RS Bearing Applications

• Automotive wheel hub bearings and tensioner bearings — exposed to road splash, mud, and temperature cycling.
• Agricultural machinery: seed drills, ploughs, and harvester drives operating in fine soil and grit.
• Food and beverage processing equipment requiring wash-down resistance (EPDM or HNBR seal variants).
• Pumps, compressors, and HVAC equipment in outdoor or semi-outdoor installations.
• Conveyor systems in mining, quarrying, cement, and other heavy-dust environments.
• Medical devices, laboratory instruments, and clean-room equipment where sealed-for-life operation eliminates maintenance intervals.

Direct Comparison: Open vs ZZ vs 2RS at a Glance

Single-Side vs Double-Side Variants: Z, ZZ, RS, and 2RS

It is worth noting that single-sided variants also exist: a bearing designated Z has one metal shield, and a bearing designated RS (or RS1) has one rubber seal, leaving the opposite face open. These are used in specific arrangements where:

• One side of the bearing faces a clean, oil-lubricated environment (open side faces the oil) while the other side faces a dirty or external environment (shielded or sealed side faces outward).
• A grease nipple feeds lubricant in from one side, requiring the opposite side to be open or shielded (not sealed) to allow old grease to purge.
• Space or thermal constraints make a fully sealed bearing impractical.

In the majority of new designs, double-sided protection (ZZ or 2RS) is the standard specification, as it provides symmetric grease retention and contamination exclusion regardless of bearing orientation.

Seal Material Variants Within the 2RS Family

Not all 2RS bearings use the same rubber compound. The seal material must be matched to the operating temperature range and any chemical exposure the bearing may encounter. The main options are:

Using the wrong seal material is a common and costly mistake. Fitting a standard NBR-sealed bearing in a continuous 140°C application, for example, will cause the seal rubber to harden and crack within a few hundred hours — allowing lubricant loss and contamination entry that would not have occurred with an HNBR or FKM seal.

Effect on Bearing Noise and Vibration

Sealing arrangement also influences noise levels, which matters in electric motors, domestic appliances, medical devices, and office equipment where quiet operation is a design requirement.

• Open bearings generate the lowest intrinsic noise from the bearing itself, as there is no seal contact friction. However, in contaminated environments they generate more noise as raceway wear progresses.
• ZZ bearings produce a characteristic low-frequency "hiss" from the interaction of grease with the metal shield at high speeds — perceptible in some high-precision motor applications.
• 2RS bearings produce slightly higher baseline noise due to seal contact torque variation, but their superior contamination exclusion means noise levels remain stable over a longer service life compared to Open or ZZ bearings in dirty environments.

For low-noise precision applications — office printers, medical instruments, servo motors — specify bearings to a noise grade (ABEC 3 or ABEC 5 and above), and consult the manufacturer's vibration test data (typically expressed as Anderon levels or dB(A) values) in addition to the sealing specification.

Common Specification Mistakes and How to Avoid Them

The following errors account for a significant proportion of premature deep groove ball bearing failures in service:

1. Using ZZ in wet or wash-down environments. The non-contact gap allows water ingress, leading to grease washout and raceway corrosion. Always specify 2RS (with EPDM or HNBR seal) for any exposure to water, steam, or cleaning fluids.
2. Using 2RS above the speed limit. Running a 2RS bearing continuously above its reference speed generates excessive frictional heat at the seal lip, accelerating grease degradation and seal wear. If speed demands exceed the 2RS limit, consider a 2RZ or low-friction sealed variant, or re-evaluate housing sealing to allow a ZZ or Open bearing.
3. Mixing grease types when re-lubricating Open bearings. Incompatible grease base oils and thickener systems can cause the grease to liquefy, lose viscosity, and fail to maintain an adequate film. Always identify the existing grease type before adding new lubricant.
4. Assuming ZZ and 2RS are interchangeable on the same drawing. Some maintenance teams substitute ZZ for 2RS (or vice versa) because the bearing dimensions are identical. This is a significant error — the sealing performance difference can reduce service life by a factor of 3–10 in contaminated conditions.
5. Ignoring seal material compatibility at elevated temperatures. Standard NBR seals are not rated above 120°C. In applications such as oven conveyor drives, dryer bearings, or engine bay components, always specify HNBR, FKM, or a ZZ variant with a high-temperature grease fill.

Decision Guide: Choosing the Right Variant for Your Application

Use the following criteria to select the correct deep groove ball bearing variant:

Summary: The Right Choice in Each Scenario

The Open, ZZ, and 2RS suffixes represent three fundamentally different approaches to protecting a deep groove ball bearing. Open bearings maximise speed and allow external lubrication; they suit high-speed precision equipment with managed lubrication systems. ZZ bearings balance speed with basic grease retention and particle exclusion; they are the workhorse of clean, dry, moderate-speed machinery. 2RS bearings deliver the highest contamination exclusion and longest maintenance-free life; they are the specification of choice wherever moisture, dust, or aggressive environments are present.

When in doubt between ZZ and 2RS for a new design, the practical default is 2RS with a standard NBR seal — it covers the widest range of operating conditions, and the modest speed penalty is rarely a limiting factor in general industrial applications below 10,000 rpm. Reserve ZZ for applications where you can confirm dry, clean conditions and the speed advantage is genuinely needed.