ZZ vs 2RS Bearings. Shielded vs Sealed Explained

What Is a ZZ Shielded Bearing

ZZ indicates a deep groove ball bearing with two metal shields, one pressed into each side of the outer ring. The shields are stamped from SPCC steel sheet, typically 0.3 mm to 0.5 mm thick depending on bearing size. A 0.05 mm to 0.10 mm gap remains between the shield bore and the inner ring shoulder. This non-contact design means zero friction from the shield itself.

The gap lets the bearing run at its full speed rating. The trade-off: that same gap allows fine dust particles under 0.05 mm and humidity to enter over time. ZZ shields protect against coarse debris like metal chips, sand, and fiber, but offer limited defense against water spray, coolant mist, or submicron particles.

ZZ bearings ship with a measured grease fill: 25% to 35% of the free internal volume for standard applications. At high RPM, centrifugal force pushes grease outward, and the shields retain roughly 60% to 70% of the original fill over the bearing’s service life. For clean, dry environments with moderate contamination risk, ZZ is the standard choice across electric motors, power tools, office equipment, and home appliances.

What Is a 2RS Sealed Bearing

2RS stands for two rubber seals, one on each side. Unlike ZZ shields, the seal lip makes light contact with the inner ring groove. The seal body is NBR (nitrile butadiene rubber) bonded to a steel insert for structural rigidity. The contact pressure is controlled to 0.02N to 0.05N per seal, adding a small friction torque that reduces maximum speed by 15% to 20% compared to the ZZ version of the same bearing.

The contact lip creates an effective barrier. 2RS seals block particles down to 0.01 mm and prevent moisture ingress at relative humidity up to 95%. A 696 2RS bearing at 37,000 RPM still runs fast enough for most applications while keeping the factory grease fill intact at 85% to 90% retention over the bearing’s life. NBR seals operate from -40°C to 100°C. For higher temperatures, FKM (Viton) seals extend the range to 180°C, available through OEM customization.

What Is an RS Bearing (Single Rubber Seal)

RS designates a single rubber seal on one side. The opposite side remains open or uses a metal shield, depending on the manufacturer’s configuration. This hybrid approach serves two specific use cases. First: applications where one side faces a clean cavity while the other side needs contamination protection, common in motor end bells and gearbox input shafts. Second: assemblies where the bearing must be pressed onto a shaft from the open side after the sealed side is already positioned.

RS bearings are less common in standard catalogs than ZZ or 2RS variants. Most engineers default to 2RS for full sealing or ZZ for maximum speed. RS becomes relevant when the assembly process or the load path dictates asymmetric protection, a detail that appears in roughly 5% of bearing applications based on OEM project data from Yuanhe.

ZZ vs 2RS vs RS. Full Comparison

How to Choose Between ZZ and 2RS

Open Bearings. The Unshielded Baseline

For completeness, an open bearing carries no shields or seals. The balls and raceways are exposed. This configuration allows the highest possible speed because there is zero shield drag, but it demands an external sealing system built into the housing. Open bearings are used in oil-bath lubrication systems, precision spindles where every watt of friction counts, and gearboxes with pressurized oil supply. They require the user to supply their own grease or oil, making them unsuitable for sealed-for-life applications.

Open bearings are the starting point for custom lubrication strategies. If your application runs above 60,000 RPM or operates in a vacuum environment, an open bearing with specialty oil or dry lubricant may be the only viable option. For standard industrial applications, ZZ and 2RS cover over 90% of use cases without the added complexity of external sealing.

Frequently Asked Questions