How to Read Bearing Codes: 2RS, ZZ, C3 Explained

Parts of the code

Most bearing codes follow the same pattern. Example: a deep groove ball bearing for a 25 mm shaft, sealed on both sides, with larger clearance.

61 22 053 -2RS4 C35

16

Bearing type

6 is a deep groove ball bearing, 7 an angular contact ball bearing. Four-digit codes starting with 3 (3205) are double row angular contact bearings, and five-digit codes starting with 30 or 32 (30205) are tapered roller bearings.

22

Dimension series

Shows how heavy the bearing is for the same bore: 0 light, 2 medium, 3 heavy, 4 extra heavy.

305

Bore code

From 04 up, the code × 5 gives the bore: 05 × 5 = 25 mm. Smaller bores are in the table below.

4-2RS

Shield / seal

Rubber seals on both sides. Z and ZZ mean metal shields; RS and 2RS mean rubber seals.

5C3

Internal clearance

Larger than normal clearance. If no clearance is shown in the code, it is normal (CN).

Result: 6205-2RS — 25 × 52 × 15 mm deep groove ball bearing, sealed on both sides, with C3 clearance.

Bore code table

Code	00	01	02	03	04	05	06	08	10	20
Bore (mm)	10	12	15	17	20	25	30	40	50	100

Exceptions: below 10 mm the last digit is the bore itself: 608 → 8 mm. Codes with a slash give the bore directly: 62/22 → 22 mm. The same bore code is used by other common types: self-aligning ball (1205, 2205), spherical roller (22205), cylindrical roller (NU205), thrust ball (51105).

Dimension series: same shaft, different bearing

All the bearings below fit a 25 mm shaft; the outside diameter and width change with the series. That is why one series cannot replace another.

Series	Example	d × D × B	Characteristics
6000 series (light)	6005	25×47×12 mm	Narrow, thin section; high speed at moderate load. Common in electric motors and fans.
6200 series (standard)	6205	25×52×15 mm	The best-selling series on the market. Its balance of load and size suits the widest range of uses.
6300 series (heavy)	6305	25×62×17 mm	Thicker than the 6200 at the same bore and carries more load. Preferred in agricultural and construction machinery.
6400 series (extra heavy)	6405	25×80×21 mm	The heaviest section, for special applications with high radial load. Usually open type only.
16000 series (narrow)	16005	25×47×8 mm	Same outside diameter as the 6000, narrower width. Usually open type.
6900 / 61900 series (thin)	6905	25×42×9 mm	Thin section, slightly higher load than the 6800. Bicycles, motorcycles, light machinery.
6800 / 61800 series (extra thin)	6805	25×37×7 mm	Very thin section, for tight spaces: bicycle hubs, robotics, office machines.

Shields and seals: Z, ZZ, RS, 2RS

Shields and seals keep dust and water out of the bearing. A metal shield (Z) does not touch the ring; a rubber seal (RS) rubs on the ring, so it protects better but lowers the speed limit. A leading 2 means both sides are closed.

Open 6205 No seals or shields. Lubricated from outside; the highest speed capability. ≈ 15,500 rpm speed limit Single shield 6205-Z Metal shield on one side. Non-contact, so it adds no friction; it keeps dust out but lets water through. ≈ 14,260 rpm speed limit Double shield 6205-2Z (ZZ) Metal shields on both sides, greased for life. Being non-contact, it runs faster than a sealed bearing. For dry and dusty conditions. ≈ 13,175 rpm speed limit Single seal 6205-RS Rubber seal on one side. A contact seal, so it seals better. ≈ 10,850 rpm speed limit Double seal 6205-2RS Rubber seals on both sides, greased for life. The best protection against dust and water; seal friction keeps its speed below the shielded version. For damp and dirty conditions. ≈ 8,525 rpm speed limit

Speeds are approximate values calculated for the 6205; check the manufacturer's catalog for exact values.

How each brand writes it (6205)

The size is the same in every brand; only the way the suffix is written differs.

Type	SKF	FAG	NTN	Timken	NACHI	Koyo	SNR	NSK
Open	6205	6205	6205	6205	6205	6205	6205	6205
Single shield	6205-Z	6205-Z	6205Z	6205-Z	6205ZE	6205 Z	6205.Z	6205Z
Double shield	6205-2Z	6205-2Z	6205ZZ	6205-ZZ	6205ZZE	6205 ZZ	6205.ZZ	6205ZZ
Single seal	6205-RS1	6205-RSR	6205LU	6205-RS	6205NSE	6205 RS	6205.E	6205DU
Double seal	6205-2RS1	6205-2RSR	6205LLU	6205-2RS	6205-2NSE9	6205 2RS	6205.EE	6205DDU

ZZ or 2RS? Use ZZ in dry, dusty and high-speed places; use 2RS where there is water, moisture or fine dust. Shielded and sealed bearings are greased for life.

Internal clearance: CN, C3, C4

Internal clearance is the small amount of play between the balls and the rings. When a bearing warms up, the inner ring expands and this clearance shrinks; if it is too small, the bearing binds and runs hot.

CN

Normal

Standard clearance. Not shown in the code; suits most general applications.

C3

Larger than normal

Where the bearing runs warm or has a tight fit; common in electric motors and high-speed shafts.

C4

Larger than C3

For special applications with bigger temperature differences or tighter fits.

How each brand writes C3 (6205-2RS)

	SKF	FAG	Timken	NACHI	Koyo	NTN	SNR	NSK
C3	6205-2RS1/C3	6205-2RSR-C3	6205-2RS-C3	6205-2NSE9 C3	6205 2RSC3	6205LLUC3	6205.EEC3	6205DDUC3

Note: do not replace a C3 bearing with a normal-clearance one; it may bind when it warms up. If you are not sure, send us the code on the old bearing.

Cage types

The cage keeps the balls evenly spaced. Its material is shown by a suffix at the end of the code; the standard steel cage is usually not shown.

Material	Example suffixes	Where it is used
Pressed steel	Usually not shown · SKF J	General use; the standard cage.
Polyamide (glass-fibre reinforced)	SKF TN9 · FAG TVH, TVP	Quiet, light running; electric motors. Not recommended above about 120 °C.
Brass	SKF M, MA · FAG M	Vibration, shock and high temperature.

Lubrication

ZZ and 2RS bearings are greased at the factory. They need no extra grease; do not remove the shield or seal to regrease them.
For an open bearing, fill the bearing itself with grease; filling about 30–50% of the free space in the housing is enough. Use less grease at high speed.
Too much grease makes the bearing run hot and breaks the grease down early.
Do not mix different types of grease; incompatible greases can lose their consistency.

Fitting and removal

Apply force to the ring with the tight fit: to the inner ring if the bearing is tight on the shaft, to the outer ring if it is tight in the housing. If the force passes through the balls, the raceways get dented.
Do not hit the bearing directly with a hammer; use a fitting sleeve or a press.
When fitting with heat, use an induction heater. Do not heat a standard bearing above 120 °C, or a shielded or sealed bearing above 80 °C; never use an open flame.
To remove a bearing, use a puller. Refitting a removed bearing is not recommended.

Code unreadable? Find it by size

Measure the bore (d), outside diameter (D) and width (B) with calipers.
Type the size into the search on the Bearings page, for example 25x52x15.
From the shield and seal types of that size (open, ZZ, 2RS), choose the one that matches the old bearing.

If you are not sure, send a photo of the bearing on WhatsApp and we will find the code.

d: bore · D: outside diameter · B: width

Frequently asked questions

Are the 6205 and the 6205-2RS the same size?

Yes. Both are 25 × 52 × 15 mm; the only difference is that the 2RS has rubber seals on both sides. All shield and seal types of this size are on the 6205 page.

Are the SKF 6205-2RS1 and the NSK 6205DDU the same bearing?

They have the same dimensions and seal type, so they are equivalents. Brands write the suffix differently, and the internal design and grease may vary by brand.

Is there a difference between ZZ and 2Z?

No. Both mean metal shields on both sides; SKF and FAG write 2Z, most other brands write ZZ.

What does it mean if the code does not say C3?

The internal clearance is normal (CN). Normal clearance is not shown separately in the code.

Can a 6305 be fitted instead of a 6205?

No. Both have a 25 mm bore, but the 6305 has a larger outside diameter (62 mm) and width (17 mm); it will not fit the housing.

Does a sealed (2RS) bearing need greasing?

No. Shielded and sealed bearings are greased for life at the factory; they need no extra lubrication.