Bearing Designations and Sizes
Read a supported bearing code, then use the manufacturer's catalog for its outside diameter, width and full specification.
Read the basic designation before the extra letters
Read the basic designation before the extra letters
A bearing number is a compact description, not a universal sizing formula. Start with the maker and the bearing family. A basic designation identifies a series and bore; prefixes and suffixes add details. The same letters can mean different things in different families or manufacturers' catalogs.
For the ordinary metric deep-groove example 6205, read 6 | (0)2 | 05: type 6 is deep-groove ball; 02 is the dimension series, with width-series 0 omitted in the written number; bore code 05 means 25 mm. The diameter-series digit 2 is not an outside diameter in millimetres.
Width-series digits can be omitted differently: NSK lists 6005 as 6 | (1)0 | 05, and 6305 as 6 | (0)3 | 05. Parentheses here explain the omitted digit; they are not characters to add to an order. See NSK's bearing-series table.
Recognize the geometry first in Bearing Types and Loads. A matching bore alone does not make two bearings interchangeable.
The same bore can come with a different outside diameter and width; Interactive
The same bore can come with a different outside diameter and width
Compare the three catalog rows below. d is the bore, D the outside diameter and B the width. Their 25 mm bores are equal, while their housing and axial-space requirements differ. The picture keeps one scale so that this difference is visible.
All three are single-row deep-groove ball bearings. The bore code is 05 → 25 mm; the other dimensions below are catalog values, not digit arithmetic.
| Basic designation | d · bore | D · outside | B · width | Dimension series |
|---|---|---|---|---|
| 6005 | 25 | 47 | 12 | 10 (width 1 omitted in code) |
| 6205 | 25 | 52 | 15 | 02 (width 0 omitted in code) |
| 6305 | 25 | 62 | 17 | 03 (width 0 omitted in code) |
These are nominal boundary dimensions. Shaft and housing fits, shoulder dimensions, corner radii, internal clearance and tolerances still require the complete catalog entry and the application design.
00, 01, 02 and 03 are the bore-code exceptions
00, 01, 02 and 03 are the bore-code exceptions
| Bore code | Bore d | How it is read |
|---|---|---|
| 00 | 10 mm | Special code |
| 01 | 12 mm | Special code |
| 02 | 15 mm | Special code |
| 03 | 17 mm | Special code |
| 04–96 | 20–480 mm | Code × 5 mm, where this coding system applies |
Thus 6202 has a 15 mm bore, not 10 mm; 6205 has a 25 mm bore. This rule supplies only the bore. It does not calculate D or B.
Do not apply it blindly to miniature, inch, letter-coded or special bearings. Slash forms can state the bore directly: NSK gives 63/22 as 22 mm and 230/560 as 560 mm. Its miniature 688 example has an 8 mm bore. NSK excludes double-direction thrust ball bearings from its general 04–96 rule.
Primary references for the bore-code scope
NSK, Bearing Designation Systems, section 1.2, explains the special and direct-size forms. NSK Technical Insight TI/E/0111, page 4 note 3, scopes the 04–96 rule and names the thrust-bearing exception.
Series identify a family; the catalog supplies the envelope
Series identify a family; the catalog supplies the envelope
| Series examples | Family |
|---|---|
| 60, 62, 63 | Deep-groove ball |
| 72, 73 | Angular-contact ball |
| 12, 13, 22, 23 | Self-aligning ball |
| NU2, NJ2, NUP2 | Cylindrical roller; letters distinguish rib arrangements |
| NA48, NA49 | Needle roller |
| 302, 303, 320 | Tapered roller |
| 222, 223, 230 | Spherical roller |
| 511, 512 | Thrust ball |
| 292, 293, 294 | Spherical roller thrust |
A dimension series selects a standardized size family; it is a table key, not a digit-to-millimetres formula. Series examples follow NSK's designation guide. Different types also use different dimension letters. A tapered bearing distinguishes inner-ring width B, outer-ring width C and assembled width T. Thrust catalogs may label axial height T or H: use that manufacturer's diagram rather than substituting B automatically.
| Manufacturer and designation | d | D | Axial dimensions in that catalog |
|---|---|---|---|
| NSK HR30205J | 25 | 52 | T = 16.25 overall; B = 15 inner ring; C = 13 outer ring |
| ING 51105 | 25 | 42 | H = 11 overall height |
The 15 mm inner-ring width of HR30205J is not its 16.25 mm assembled width. These examples are not added to the three-row deep-groove viewer above. NSK's boundary-dimension diagrams also distinguish radial width from thrust height.
C3 means internal clearance, not accuracy or a loose shaft fit
C3 means internal clearance, not accuracy or a loose shaft fit
Internal clearance is movement between a bearing's rings under the specified measuring conditions. A fit is the relationship between a ring and its shaft or housing seat. A precision class specifies dimensional and running accuracy. These are different quantities; see NSK's explanation of fits and clearance.
| Suffix | Meaning | What it does not tell you |
|---|---|---|
| ZZ | Shields on both sides of the ball bearing | Not a load rating |
| DDU | Contact rubber seals on both sides | Not a universal seal code for every maker |
| VV | Non-contact rubber seals on both sides | Not the same sealing arrangement as DDU |
| C3 | Radial internal clearance greater than CN, for the radial-bearing context shown | Neither a precision class nor a shaft/housing fit |
| P6 | ISO tolerance class 6 | Not an internal-clearance group |
Prefixes matter too: NSK uses HR for its high-capacity tapered roller series. Read the complete maker-specific designation, including cage and lubrication details where required. Seals and shields affect exclusion of contaminants, friction and speed limits; they do not replace the catalog's load ratings. Sources: NSK TI/E/0111, auxiliary-symbol tables; NSK Bearing Designation Systems, sections 2 and 3.
For load direction and the existing basic rating-life calculation, return to Bearing Types and Loads. For how the bearing is located on a machine, see Shaft Support and Axial Adjustment.