2Z or 2RSR — shields or contact seals
The same bearing with shields runs up to twice as fast as the sealed version. A contact seal, in return, holds out dust and moisture that a shield will not. Below is the difference in figures from the datasheets.
Short answer
High speed and a clean environment — shields (2Z). Dust, moisture, wash-down or outdoor work — contact seals (2RSR, on some designs 2HRS).
A shield does not touch the inner ring, so it adds no friction and no heat. A seal presses its lip against the ring — it protects better, but costs speed.
A shield buys speed. A seal buys a clean interior.
What sealing costs — in revolutions
We compared limiting speeds from the manufacturer's datasheets for the same sizes in both designs. The difference is not a one-off — it repeats across the whole series.
| Size | with 2Z shields | with 2RSR seals | difference |
|---|---|---|---|
| 6203 | 24,200 rpm | 16,100 rpm | +50% |
| 6204 | 20,075 rpm | 13,865 rpm | +45% |
| 6205 | 17,976 rpm | 11,308 rpm | +59% |
| 6206 | 14,433 rpm | 8,846 rpm | +63% |
| 6207 | 11,831 rpm | 6,320 rpm | +87% |
| 6208 | 10,533 rpm | 5,789 rpm | +82% |
The larger the bearing, the wider the gap — at 6208 a shield allows nearly twice the speed.
When a seal anyway
Limiting speed is a catalogue value, not what most machines run at. An electric motor at 1,450 rpm, a conveyor, a fan or a gearbox comes nowhere near any figure in the table — the lost speed then costs nothing, while protection from dust decides whether the bearing survives the season.
A shield stops chips and coarse dust, but neither water nor fine dust. In dusty work, pressure washing or outdoors, the contact seal is the choice — without hesitation.
What neither design replaces
A sealed bearing is greased at the works and not meant for relubrication — it runs as long as the grease lasts. In an arrangement meant to work for years under load, an open design with external or oil-bath lubrication is used. That is why our catalogue holds 25,746 open items and under 2,500 sealed ones in total.
The second limit is temperature. Standard seals work to roughly 100 °C; above that you reach for special designs or an open bearing with suitable grease.
A sealed design is convenience, not unlimited service life.
Source
Limiting speeds — the “Limiting speed” field from the manufacturer's datasheets in our database, averaged per size for 2Z and 2RSR/2HRS designs (measured 14 Sep 2026). Item counts — our catalogue: 1,237 shielded, 1,245 sealed, 25,746 open.