Originally Posted by DaveRS23
There are different levels of precision within the same part number of bearings. Which impacts the price outside of 'markup' and even brand.

'Some applications demand a high level of precision that cannot be achieved with standard tapered roller bearings. This includes many machining, printing press and rolling mill applications where combinations of tight tolerances, high speeds and radial and thrust loads are present. For more than 50 years, The Timken Company has offered a wide array of precision-class tapered roller bearings that deliver superior accuracy and control in critical applications.

Different Levels of Precision Meet Critical Needs
The more demanding the precision objective, the more accurate the bearing must be. Timken provides four precision classes, in both metric
and inch systems, that cover the full range of precision application requirements. In ascending order of accuracy, they are identified in the metric system as Class C, B, A and AA, while in the inch system as Class 3, 0, 00 and 000. The chart below summarizes the accuracy of Timken precision bearings as compared to standard bearings. All Timken precision bearings have an electrolyte acid dot etched on both
faces of each cone and cup. This dot indicates the high point of the cone and cup run-out, respectively, and is used when mounting to obtain the best performance'

www.timken.com/resources/precision-tapered-roller-bearings-brochure

'The Annular Bearing Engineering Committee (ABEC) created a rating system that has become the industry standard for ball and roller bearing tolerances. ABEC includes five tolerances classes: 1, 3, 5, 7, and 9 with 1 being the widest and 9 the tightest. Thus, bearings with a higher ABEC rating have tighter tolerances, and that means better precision, higher efficiency, and the potential to accommodate applications requiring high speeds.

It is important to note that a bearing in a higher ABEC class does not imply that the bearing can carry a higher load, rather it can carry the same load as an analogous bearing with a lower rating but at higher speed, thanks to its more controlled runout and smaller endplay. ISO has an equivalent standard (ISO 492) for bearing tolerances that corresponds to the ABEC ratings as follows: normal class 6x (tightest), 6, 5, 4, and 2.

The ABEC tolerance classifications specify both tolerances of size and form for the individual inner and outer rings. The critical features of the rings include the bore (or inner diameter of the inner ring), the outer diameter of the outer ring, the ring widths, and the raceways of each ring. Tolerances of form include roundness, taper, runout, and parallelism.'

https://blog.emersonbearing.com/blo...wisely-how-fast-your-bearings-need-to-go

I saw this on my airplane wheel bearings that had to have a bearing part # with a G suffix on it to be FAA legal, 4 times more money than the standard automotive wheel bearings work

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)