Short answer: a bearing code is built from a prefix (type or material), a series number, a bore code and a suffix (shields, seals and other options). In 623ZZ, "62" is the series, "3" is the 3 mm bore and "ZZ" means two metal shields. In MR105-2RS, "MR" is metric miniature, "105" means 5 mm bore and 10 mm outside, and "2RS" means two rubber seals. An F or MF prefix means flanged.
Bearing numbers explained: the basic structure
Most ball bearing designations follow the scheme used across the industry and in ISO 15, which standardises the boundary dimensions behind each number. Read the code from left to right:
- Prefix: letters that describe the type or a variant, such as MR (metric miniature), F or MF (flanged) or S (stainless at some makers).
- Series: the digits that set the bearing type and the width and diameter class, for example 6 for a single-row deep groove ball bearing.
- Bore code: the last one or two digits, which give the bore.
- Suffix: letters after the number for closures, internal clearance, cage or precision, such as ZZ, 2RS or C3.
Manufacturers add their own codes on top, so always compare with the dimensions as well as the letters.
How to read the bore code
For bearings with a bore of 10 mm or more, the last two digits are the bore code: 00 = 10 mm, 01 = 12 mm, 02 = 15 mm and 03 = 17 mm. From 04 upwards, multiply by 5, so 6204 has a 20 mm bore. That is why the 6000ZZ and the 6200ZZ both have a 10 mm bore, and the 6001ZZ has 12 mm.
For miniature bearings below 10 mm, the last digit simply is the bore in millimetres. A 623 has a 3 mm bore, a 625 5 mm and a 608 8 mm.
Series digits: 60, 62, 68 and 69
The first digits after the type number give the dimension series. For the same bore, a 68 series bearing is the thinnest, a 69 series is a little larger, the 60 series larger again and the 62 series is wider and heavier. Compare the 8 mm bore bearings: 688 is 8 x 16 x 5 mm, 698 is 8 x 19 x 6 mm and 608 is 8 x 22 x 7 mm. For the 3 mm bore: 683 3 x 7 x 3, 693 3 x 8 x 4 and 623 3 x 10 x 4 mm. The full list is in our bearing size chart.
MR bearing codes
MR codes work differently. After "MR" come the bore and the outer diameter in millimetres, run together: MR105 = 5 mm bore, 10 mm outside; MR148 = 8 mm bore, 14 mm outside; MR52 = 2 mm bore, 5 mm outside. The width is not in the code (the MR105 is 4 mm wide, the MR106 3 mm), so check it on the product page. Our MR series runs from MR52ZZ to MR148ZZ.
Flanged bearing codes: F and MF
An F in front of a 6xx number means the same bearing with a flange on the outer ring: F623ZZ is a flanged 623ZZ and F608ZZ a flanged 608ZZ. MF is the flanged version of an MR bearing, so MF105ZZ is a flanged MR105ZZ. The flange diameter and width are not in the code; they are listed in our flanged bearings collection and on each product page.
Suffix codes: ZZ, 2RS, Z, RS and open
| Suffix | Meaning | Common brand equivalents |
|---|---|---|
| Z | One metal shield | SKF Z, NSK Z |
| ZZ | Two metal shields (non-contact) | SKF 2Z, NSK ZZ |
| RS | One rubber contact seal | SKF RS1, NSK DU |
| 2RS | Two rubber contact seals | SKF 2RS1, NSK DDU |
| (none) | Open, no shields or seals | - |
| UU | On LM linear bearings: rubber seals at both ends | - |
The difference between shields and seals is covered in our ZZ vs 2RS guide. Other suffixes you may meet are C3 (internal clearance larger than normal) and cage codes; they matter for heavy loads and high temperatures but rarely for miniature bearings in hobby and repair use.
Stainless steel codes: SS and S
There is no single industry code for stainless steel bearings. Some manufacturers put an S in front (S623ZZ, SMR105ZZ), others add SS at the end. On our site the stainless versions carry "SS" after the code, for example 623ZZ SS and MR105ZZ SS, in AISI 440C. All of them are in the stainless steel bearings collection.
Precision classes: ABEC and P
Precision is usually shown separately from the main code. The ABEC scale (ABMA, American) and the ISO classes (written P0, P6, P5, P4, P2) describe the same tolerance steps: ABEC-1 = P0 (normal), ABEC-3 = P6, ABEC-5 = P5, ABEC-7 = P4 and ABEC-9 = P2. A higher ABEC number means tighter dimensional and running tolerances; it does not by itself mean a higher load rating or a longer life. Precision class is not stated for our bearings; if your design needs a specific ABEC or ISO class, ask us before ordering.
Worked examples
- 623ZZ: deep groove ball bearing, 62 series, 3 mm bore, two metal shields; 3 x 10 x 4 mm.
- MR105-2RS: metric miniature, 5 mm bore, 10 mm outside, two rubber seals; 4 mm wide (product page).
- F608ZZ: flanged 608, 8 x 22 x 7 mm with a 25 mm flange, two metal shields.
- 6000-2RS: 60 series, bore code 00 = 10 mm, two rubber seals; 10 x 26 x 8 mm (product page).
- LM8UU: linear ball bearing for an 8 mm rod, seals at both ends; 8 x 15 x 24 mm (product page).
Cross-referencing bearing numbers
Because the main number and the dimensions are standardised, a bearing from one brand can usually be replaced by one with the same number from another. Check three things: the dimensions (d x D x B, plus the flange if any), the closure (ZZ or 2RS, which you can swap if the conditions allow) and the material. If the old bearing has an unusual suffix you cannot place, look it up in that manufacturer's catalogue designation table before you order.