Quick and Dirty
If any bearing is being purchased, utilized, etc. that does not clearly state its precision class, then it is considered non-precision and is below A1/P0. This does not speak to the quality of the bearing. Precision speaks to the tolerance level of all the dimensions of the bearing. Dimensions are very different than quality, and trust in the brand is a third aspect all together much more correlated to quality.
The higher (tighter) the precision, the higher the cost – period. This is a manufacturing statement, not a sales statement. The only way this rule is not true is with volumes that are able to drive down costs in certain areas to create a situation where a higher precision could be purchased for less than a lower precision – do not expect this to happen often. An example would be a distributor who orders 10,000 pieces of an A5/P5 and 10 pieces of a A3/P6. In this instance the A5/P5 price may actually be lower.
Precision classes consist of ABEC, DIN and ISO. These originated in the USA, Germany, and England, respectively. But these bearing precision classes are used widely within the bearing industries’ around the world. There are some companies who have created custom tolerancing, but let’s make one thing very clear – ABEC, DIN, and ISO are the internationally accepted bearing regulatory bodies and tolerances within the bearing production world. There are combinations of working engineers and standards engineers who create and maintain these tolerances.
A small exception to this rule would be some tolerancing that is becoming generally accepted out of Asia. This consists of ‘Noise’ Grades – i.e. ‘Z2’ – that exist below A1. These have been created to further dissect/stratify the non-precision realm of bearings below A1/P0.
Bearing Tolerance Classes
The big 3 internationally accepted tolerance classes; ABEC, DIN and ISO have equivalents throughout their respective ranges. This can be seen in the table. Don’t be fooled by a fast talker that there is a difference between equivalents in this table – i.e. A1 and P0 are internationally accepted to be the same.
ISO classes are a far third place to both ABEC and DIN standards. One can go many years within the bearing industry and never run across a manufacturer calling out an ISO class only – at least from a ball bearing perspective.
The American National Standards Institute (ANSI) is the controlling body above the American Bearing Manufacturers Association (ABMA) which created and oversees the ABEC tolerances. DIN was originally created in Germany and ISO was originally formed in England. These organizations are made up of both private company and government engineers. Today however, these organizations work together for a common goal of creating acceptable tolerances for the bearing industry as a whole to promote commerce around the world. If bearing standards did not exist, then tolerancing from different manufacturers could potentially be very different which in turn would greatly hurt the consumer/user. For this reason the tolerance organizations have achieved a great deed for all within the bearing industries to create and enforce these bearing standards.
|ANSI Standard 20*||DIN 620*||ISO 15, 355, 492, & 8443 *|
|ABEC 3||P6||Class 6|
|ABEC 5||P5||Class 5|
|ABEC 7||P4||Class 4|
|ABEC 9||P2||Class 2|
*Chamfer and other minor dimensions may be called out in other standards.
Bearing Precision Classes
When comparing different precision classes note where the ‘jumps’ in both precision and cost exist. From ABEC 3 to ABEC 5 and from ABEC 5 to ABEC 7 are larger jumps than other steps in precision. This is true to the extent that many factories do not produce ABEC 1 bearings intentionally. The production line intends to produce ABEC 3 bearings and then the ‘fallout’ or extra bearings would be sold as ABEC 1. For this reason it is fairly normal to purchase an ABEC 3 for a minimal price increase from an ABEC 1. The price generally will jump a bit moving to ABEC 5 and then another large jump to ABEC 7. Factories that produce very large volumes – tens of thousands or more a day – of ABEC 3 bearings may not produce ABEC 5 bearings in the same factory. Furthermore, a production facility that produces ABEC 7 and ABEC 9 bearings will almost certainly not produce lower precision in the same building. One of the main reasons for this is the large difference in the mindset of the employee, machines, capabilities, speed, etc. A master grinder creating mirror finishes on a ABEC 9 raceway is vastly different than a generally skilled machinist producing ABEC 1 bearings. Furthermore, it is becoming common for lower precision bearings, ABEC 1 and ABEC 3, to have automated factories. This is quite difficult and costly for ABEC 7 and ABEC 9 production, even though with volumes it is possible.