Open vs Shielded vs Sealed: Which Bearing Closure to Choose

Three ways to close a bearing

Deep groove ball bearings come in three closure variants. The choice trades off protection against contamination against friction and speed capability:

Closure	Code example	Protection	Friction	Relubrication
Open	6204	None	Lowest	Required (external)
Metal shield	6204-ZZ	Moderate (dust)	Very low	Not possible
Rubber seal	6204-2RS	High (dust + moisture)	Higher	Not possible

Open bearings

An open bearing has no closure at all — you can see the balls and cage from the side.

Choose open when:

• The bearing runs inside a sealed, clean housing (gearbox, motor with its own seals)
• The housing provides oil bath or circulating lubrication
• Maximum speed and minimum friction matter

Open bearings achieve the highest limiting speeds because nothing touches the rotating ring. All speed ratings in manufacturer catalogs are based on open bearings unless stated otherwise.

Metal shields (Z / ZZ)

A thin steel shield is pressed into the outer ring, leaving a narrow gap to the inner ring — it does not touch it.

• Z = shield on one side, ZZ = both sides
• Filled with grease at the factory, lubricated for life
• Blocks larger dust particles, but not fine dust or moisture
• Almost no added friction: speed ratings close to open bearings

Choose ZZ when: the environment is reasonably clean and dry, you want maintenance-free operation, and speed still matters — electric motors are the classic application.

Rubber seals (RS / 2RS)

A rubber lip is molded into the outer ring and touches the inner ring, forming a real barrier.

• RS = seal on one side, 2RS = both sides
• Pre-greased and lubricated for life
• Keeps out dust, water splash and humidity
• Contact friction lowers the limiting speed — typically to around 60 % of the open bearing’s grease limit

Choose 2RS when: the bearing is exposed to dust, dirt or moisture and relubrication is impractical — agricultural machinery, conveyors, wheel hubs, outdoor equipment.

Rules of thumb

1. Clean and enclosed? Open is fastest and coolest-running.
2. Indoor, dry, maintenance-free? ZZ is the default choice.
3. Dirty, humid or outdoor? 2RS — accept the speed penalty.
4. One side only? Single Z or RS exists for housings that seal one side themselves, but double-sided versions are far more common.

Note on suffixes

Suffix codes are not fully standardized between brands. SKF writes 2RS1, NSK writes DDU, FAG writes 2RSR — all mean rubber contact seals on both sides. When in doubt, check the designation breakdown on each bearing’s detail page or the manufacturer catalog.

Ready to pick a bearing? The Bearing Selection guide includes sealing as one of its four questions.