ZZ vs 2RS Bearings: Shields vs Seals, Which to Choose

Short answer: a ZZ bearing has a thin metal shield on each side that does not touch the inner ring, so it runs with low friction and suits higher speeds in clean, dry places. A 2RS bearing has a rubber seal on each side that rubs lightly on the inner ring, so it keeps dust and splashes out much better but has a little more drag and a lower speed limit. Choose ZZ for clean, fast, low-torque jobs and 2RS for dirt, moisture or outdoor use.

What does ZZ mean on a bearing?

ZZ is the common suffix for a bearing with a metal shield on both sides. One shield is written Z; two shields are ZZ. Some manufacturers use their own code for the same thing: SKF writes 2Z, NSK writes ZZ, and you will also see "2Z" on European catalogue pages. The shield is a pressed steel disc fixed in the outer ring. It leaves a very small gap to the inner ring, so it is a non-contact closure.

Because nothing rubs, a shielded bearing has almost the same low friction as an open bearing. The shield keeps larger particles out and holds the factory grease in, but it is not watertight, and fine dust or liquid can still get past the gap.

What does 2RS mean on a bearing?

2RS means a rubber seal on both sides (RS = rubber seal, 2 = two of them). The seal is usually nitrile rubber (NBR) bonded to a steel insert, and its lip touches the inner ring, so it is a contact seal. Brand codes differ again: SKF uses 2RS1, NSK uses DDU, and others write 2RS or -2RS. A single seal is written RS.

The rubbing lip is what gives 2RS bearings their better protection against dust, water splashes and dirt. It is also why they have slightly higher friction and a lower limiting speed than a shielded bearing of the same size.

ZZ vs 2RS bearings: side-by-side comparison

Exact speed and temperature limits depend on the size and the manufacturer, so always check the data sheet for the specific bearing if you are close to a limit.

Is 2RS better than ZZ?

Neither is better in general; they are built for different conditions. A 2RS bearing is better when contamination is the main risk, because a contaminated bearing wears out long before it reaches its rated fatigue life. A ZZ bearing is better when you need low torque or higher speed and the bearing works in a clean, dry place, because the shield adds almost no friction.

A useful rule of thumb: if you can see dust, grit, sawdust, water or road dirt near the bearing, pick 2RS. If the bearing sits inside a closed housing or a clean machine and you care about free spinning, pick ZZ.

Z vs 2RS bearing: what about one shield or one seal?

A bearing with a single shield (Z) or a single seal (RS) is closed on one side only. They are used where the open side faces a lubricated gearbox or another seal, so oil can reach the balls. For a bearing that works on its own, the two-sided versions ZZ and 2RS are the normal choice. The open side of a single-closure bearing gives no protection at all.

608 ZZ vs 2RS: an example

The 608 (8 x 22 x 7 mm) is the best-known example, because it sits in skateboard wheels, scooters, fidget spinners and many 3D printer spool holders. A 608ZZ spins very freely and suits a spool holder or a spinner indoors. A 608-2RS spins a little less freely by hand but copes far better with the dust and wet streets a skate wheel sees. Both have the same dimensions, so they are drop-in replacements for each other. You can compare all versions in our 608 bearings collection.

ZZ bearing greasing and lubrication

Both ZZ and 2RS bearings are filled with grease when they are made and are normally treated as lubricated for life: they are not designed to be relubricated. In practice, the life of a capped bearing is often limited by its grease rather than by the steel. Prising off a shield or seal to add grease usually bends it and lets dirt in, so in most cases replacing the bearing is the better fix once it gets rough or noisy.

If you need to relubricate regularly, an open bearing in a housing with its own seals is the better design.

What about open bearings?

An open bearing has no shield or seal at all. It has the lowest friction and can be lubricated with oil or grease from outside, which suits machines with a central lubrication system or bearings that run in an oil bath. On its own, an open bearing has no protection against dirt, so for most hobby, repair and 3D printer jobs a ZZ or 2RS bearing is easier to live with.

How to choose: a quick checklist

• Clean and dry, needs to spin freely or fast (printer idlers, fans, small spindles): ZZ.
• Dust, grit, splashes or outdoor use (wheels, RC cars, garden and workshop tools): 2RS.
• Very low torque matters most (instruments, light rotating parts): ZZ.
• Replacing an existing bearing: match the original closure unless you know the conditions have changed. The dimensions stay the same, so you can swap ZZ for 2RS or the other way round.
• Wet or corrosive conditions: consider a stainless steel bearing as well as the seal choice.

Sizes and where to find them

The closure is only one part of the code; the numbers give the size. A 623ZZ and a 623-2RS are both 3 x 10 x 4 mm, an MR105ZZ and an MR105-2RS are both 5 x 10 x 4 mm. Our guide to reading bearing codes explains the rest of the designation, and the bearing size chart lists the bore, outer diameter and width for every common size.

Browse by closure type:

• ZZ shielded bearings, for example the 623ZZ and MR105ZZ.
• 2RS sealed bearings, for example the 623-2RS, MR105-2RS and 6000-2RS.
• Stainless steel bearings in 440C, with ZZ shields.

Every product page lists the designation, the seal, the material and the exact dimensions in millimetres, so you can check the match before you order.

Related guides

• How to read bearing codes
• Bearing size chart in mm
• 3D printer bearings
• Stainless vs chrome steel bearings

Sources

• NSK, Ball bearings catalogue E1153a (shielded vs sealed features, seal temperature range)
• NSK, Bearing and linear reference guide (brand designation cross-reference)
• NSK, Rolling bearings for industrial machinery (bore number rule, seal codes)