Buy the same 6204 bearing from the same brand and you'll still face one choice: sealed (2RS) or shielded (ZZ)? The closure you pick decides how long the bearing survives contamination, how fast it can spin, and whether it can ever be re-lubricated. Here's the difference in plain terms.
The short answer, expanded
- Sealed bearings (2RS, 2RS1, DDU, EE) use rubber lips that touch the inner ring. Best protection against dust and moisture; slightly more friction and a lower speed limit.
- Shielded bearings (ZZ, 2Z, DD) use pressed-steel discs with a tiny gap — nothing rubs, so they run faster and cooler, but fine dust and water can find a way in.
- Open bearings have no closure at all — for gearboxes and housings where oil or grease is supplied externally.
How the suffix codes work
| Suffix | Meaning | Typical brands |
|---|---|---|
| 2RS / 2RS1 / 2RSR | Rubber contact seal, both sides | SKF, FAG, Timken |
| RS | Rubber seal, one side only | most brands |
| ZZ / 2Z | Metal shield, both sides | NSK, Koyo, SKF, FAG |
| Z | Metal shield, one side | most brands |
| DDU / VV | Contact / non-contact rubber seal | NSK |
| LLB / LLU | Non-contact / contact seal | NTN |
So a Timken 6203-2RS-C3 is sealed both sides with C3 internal clearance, while an NSK 6203ZZ is the same size with metal shields.
Choose sealed (2RS) for…
- Dusty, dirty or damp environments — conveyors, agricultural and construction equipment, outdoor machinery
- Washdown areas (pair with the right grease and consider stainless)
- "Fit and forget" positions where re-lubrication will never happen
Choose shielded (ZZ) for…
- High-speed applications — electric motors, spindles, fans — where a rubbing seal would build heat
- Clean-ish, dry environments
- Anywhere low torque matters (a contact seal adds measurable drag)
Three details people miss
- Sealed and shielded bearings come pre-greased for life. You can't (and shouldn't try to) re-lubricate them. If your maintenance plan includes re-greasing, spec open bearings or single-closure variants facing the contamination side.
- Electric motors usually want ZZ + C3. The extra internal clearance (C3) compensates for heat growth, and shields avoid seal drag at motor speeds.
- Non-contact seals split the difference. Suffixes like NSK's VV or NTN's LLB seal better than a shield without the friction of a full-contact lip — a good pick for higher-speed but dirty spots.
FAQ
Are sealed bearings better than shielded?
Neither is "better" — sealed wins on contamination protection, shielded wins on speed and low friction. Match the closure to the environment.
Can I replace a ZZ bearing with a 2RS?
Dimensionally yes — 6204ZZ and 6204-2RS interchange. Just confirm the application speed is within the sealed bearing's (lower) limit.
What does 2RS C3 mean?
Rubber seals both sides (2RS) plus greater-than-standard internal clearance (C3) — a common spec for motors and hot-running equipment.
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