Seal & shield suffixes across brands

Two bearings can share the same base number — say 6204 — and be completely different parts because of two letters on the end. The seal and shield suffix decides how the bearing keeps grease in and contamination out, and it is one of the few areas where every major manufacturer uses its own code. Getting it wrong is one of the easiest cross-reference mistakes to make.

The three basic configurations

• Open — no seal or shield. The lowest friction and highest speed, but no built-in protection or grease retention. Used where an external seal protects the bearing, or where it is oil-lubricated.
• Shielded — a thin metal plate (or plates) fixed to the outer ring, with a small gap to the inner ring. It keeps out larger particles and holds grease, with almost no added friction, so limiting speed is close to an open bearing. Common codes: Z / 2Z / ZZ.
• Sealed — a rubber (elastomer) seal. A contact seal lips against the inner ring: excellent sealing and grease retention, but it adds friction and lowers the top speed. A non-contact seal runs with a tiny gap: better than a shield, less drag than a contact seal. Common codes: RS / 2RS (contact), RZ / 2RZ (non-contact).

A single letter (Z, RS) usually means one side; a doubled code (ZZ, 2RS) means both sides. Sealed bearings are typically filled with grease and sealed for life.

Contact vs non-contact — the trade-off

A contact seal (2RS) touches the inner ring, so it seals well and keeps grease where it belongs — ideal for dirty, wet or wash-down environments. The price is friction: the seal drag raises the running torque and the temperature, and cuts the limiting speed, often to half or less of the open bearing. A non-contact seal or a shield gives you most of the protection with little of the drag. On a high-speed application, fitting a 2RS "for extra protection" can actually run the bearing hotter than an open one.

The cross-brand code map

This is where cross-referencing trips people up. "Double contact seal" reads differently at every maker:

So an SKF 6204-2RSH, an NSK 6204DDU, an NTN 6204LLU and a KOYO 6204-2RS are the equivalent part — a double-contact-sealed 6204 — even though the codes look unrelated. That equivalence is exactly what a good cross-reference has to spell out, because the numbers alone don't reveal it.

Does the seal change the dimensions?

For most series, no — the seal is recessed into the width of the ring, so an open 6204 and a sealed 6204-2RS share the same 20 × 47 × 14 mm envelope and are dimensionally interchangeable. A few thin or special series are exceptions, so on tight axial builds it is worth confirming. What always changes is the friction, the speed limit and the environment the bearing is suited to.

Choosing the right one

• Clean, high-speed, externally sealed → open or shielded (ZZ).
• General machinery, moderate dirt → shielded (ZZ) or non-contact (2RZ).
• Dirty, wet, wash-down, low-to-moderate speed → contact-sealed (2RS).

When you replace a sealed bearing, match the seal type first (contact vs non-contact vs shield) and only then translate the brand code. Same base number, wrong seal, is a different bearing.

General reference only; brand suffix systems have exceptions and change over time. Confirm the exact seal designation and its speed/temperature limits with the manufacturer's catalogue.