It is a standard that specifies the production of ball bearings tolerance - tolerance between the inner and outer ring of the bearing.
There are five classes of tolerance: 1, 3, 5 , 7 and 9 (each other are just a marketing trick). The higher the rating, the greater the precision, efficiency and the speed capabilities. Nevertheless, this standard does not specify the type of grease, the number of balls or the quality of the materials from which the components of the bearing are made of - therefore a higher standard does not mean a faster bearing.
ABEC bearing standard specifies many parameters. One of them is theeccentricity (roundness) of the track in the inner ring. The maximum allowableeccentricity :
- ABEC 1 : 0.0075mm
- ABEC 3: 0.0050mm
- ABEC 5: 0.0035mm
- ABEC 7: 0.0025mm
- ABEC-9 : 0.0012mm
As you can see these values are very low. Higher ABEC grade means that tolerance is lower - achieving a lower tolerance requires a longer and more precise work of machinery which greatly increases the cost of bearings production.
As you can see, producing bearings with ABEC 7 or higher grade, made from high quality materials is very expensive.
Therefore, we can be sure that:
- Cheap skates with ABEC-9 inscription on the frame
- Cheap ABEC-7 or ABEC-9 sold in the price of branded ABEC 3
will not have anything to do with the given ABEC class or, indeed their tolerance will based on ABEC scale, but the materials used in their manufacture are low quality that the final speed of the bearing will be the same as the ABEC 3 made by well-known brand.
Similarly as in the case of wheels, bearings purchase should be limited to proven companies and in both cases, low price means low quality.