Shielded (ZZ) vs Sealed (2RS) Bearings

Both shields and seals keep dirt out and grease in — but they do it differently, and the choice affects friction, speed and how well the bearing is protected. In short: a shield is a metal disc that sits close to the inner ring without touching it, while a seal is a rubber lip that contacts the inner ring. Non-contact versus contact is the whole story.

Shields (Z / ZZ)

A shield is a thin metal plate fixed to the outer ring, with a small clearance to the inner ring. Because it does not touch, it adds almost no friction.

Low friction, no extra heat — suits higher speeds and temperatures.
Protection keeps out larger particles, but not fine dust or moisture.
Designations: Z (one shield), ZZ or 2Z (two shields).

Seals (RS / 2RS)

A seal is a rubber (or rubber-on-metal) lip that rubs against the inner ring, closing the gap completely.

Better protection against dust, moisture and contamination, and better at retaining grease.
More friction and heat from the rubbing contact, higher starting torque, and a lower maximum speed.
Designations: RS (one seal), 2RS (two seals); makers also use DDU, 2RS1 and others. Low-friction non-contact seals exist too (e.g. RZ / 2RZ).

Side by side

	Shielded (ZZ)	Sealed (2RS)
Contact	Non-contact	Contact (rubbing)
Friction / heat	Very low	Higher
Max speed	Higher	Lower
Protection	Coarse debris	Dust & moisture too
Best environment	Clean, dry, fast	Dirty, damp

Rule of thumb: choose shields for clean and fast, and seals for dirty or wet. No single design wins on every count, which is why both are stocked.

Are they greased for life?

Shielded and sealed bearings are normally filled with grease at the factory. Sealed (2RS) bearings are effectively "sealed for life" — the contact seals hold the grease in and contaminants out, and they are not designed to be re-greased. Shielded bearings retain grease well but offer less of a moisture barrier.

How to spot them on the designation

The shield or seal is shown as a suffix — for example 6205-2RS (two seals) or 6205-ZZ (two shields). See the suffix decoder and our guide to reading a bearing number.

Frequently asked questions

What does 2RS mean on a bearing?

It means the bearing has two contact rubber seals (one on each side), giving good protection against dust and moisture and retaining the grease.

What does ZZ mean on a bearing?

Two metal shields (one each side). Shields are non-contact, so they add little friction and suit higher speeds, but protect less than seals.

Which is better, shielded or sealed?

Neither is universally better. Shields are best for clean, dry, high-speed duty; seals are best where dust or moisture must be kept out, accepting a little more friction and a lower speed.

Can you re-grease a sealed bearing?

Generally no — sealed (2RS) bearings are filled at the factory and run sealed for life. If re-greasing is required, an open or shielded bearing with a separate sealing arrangement is used.

More on the all-rounder these usually come on: deep-groove ball bearings.

Article 7 Shielded Vs Sealed