Sealed vs shielded bearings: 2RS, ZZ and open explained

Look at any deep groove ball bearing listing and you will see the same size offered three ways: 6205, 6205-ZZ and 6205-2RS. The boundary dimensions are identical — 25 × 52 × 15 mm — but the closures are not, and choosing the wrong one is a common cause of early failure. This guide explains the difference and how to read the closure suffixes across manufacturers.

Three basic options

The single-sided versions (Z, RS) are used when the other side of the bearing is lubricated by the machine, or faces a separate seal. Double-sided closures (ZZ/2Z, 2RS) are normally greased for life at the factory.

Shields: low friction, limited protection

A shield does not touch the inner ring. The narrow gap keeps grease in and large particles out, but fine dust and water spray can pass. Because nothing rubs, shields add almost no friction and do not limit the bearing’s speed beyond the grease itself.

Typical use: electric motors and fans in clean indoor environments, gearbox and pump bearings protected by other seals, applications where speed and low torque matter.

Contact seals: better protection, more friction

A contact seal lip presses lightly on the inner ring. That gives much better protection against dust, dirt and splashing water, but the rubbing lip adds friction, generates heat and therefore lowers the practical speed limit. The seal material also sets a temperature limit — standard nitrile rubber is fine for most industrial duty, while very hot applications need other materials or a different solution.

Typical use: agricultural machinery, conveyors, outdoor equipment, washing machines, anything exposed to dirt or water.

Non-contact and low-friction seals

Between the two sits a family of non-contact seals: an elastomer seal whose lip runs very close to — but not on — the inner ring, often with a labyrinth profile. They protect better than a shield and run cooler than a contact seal. Manufacturers market these under their own names and suffixes (for example SKF 2RZ, NSK VV, NTN LLB). If your application has failed with shields but runs too hot with contact seals, this is the option to look at.

Choosing between them

Same closure, different letters

The confusing part is naming. Each manufacturer has its own suffix system, so the same closure appears under different strings. The table below shows typical conventions for a 6205 — always confirm with the manufacturer’s own designation system, because naming changes between product generations and sizes.

So “6205DDU”, “6205-2RSR” and “6205-2RS1” all describe a 25 × 52 × 15 mm deep groove ball bearing with contact seals on both sides. They are not automatically identical products — seal design, grease, cage and clearance can still differ — but they answer the same closure question.

Catalog tip: store the closure as a field

If you maintain a bearing catalog, do not rely on the suffix string alone for filtering. Normalize it into an explicit attribute such as closure_type (open / shield / contact seal / non-contact seal) and closure_sides (one / two), and keep the original suffix next to it. That lets customers filter “sealed 25 mm bearings” across brands without merging different products. Our normalization page shows the pattern.

Common mistakes

• Removing shields to “regrease” a 2Z bearing. It is rarely worthwhile; replace the bearing.
• Fitting 2RS where a ZZ ran at high speed. The extra seal friction can overheat the bearing.
• Assuming “RS” means both sides. RS is one side; 2RS is both.
• Mixing up closure and clearance. 6205-2RS-C3 has seals and C3 clearance; see C3 clearance explained.

Apply it

Look up any size on the bearing search — each size page lists its common closure variants. For less common suffixes, use the bearing number decoder or the suffix dictionary. Normalizing closures across a whole supplier catalog? Get in touch.