ABEC Ratings are a measure of tolerance. The governing body that sets forth bearing standards is called the Annular Bearing Engineering Committee, or ABEC (pronounced A-Bek). Tolerance is how precisely the components of the bearing fit together. A more precise fit between bearing parts makes for a more smooth and efficient bearing.

Please note that just because a bearing has a higher ABEC Rating does not mean it is faster. ABEC ratings are just one feature of a bearing. Other factors such as the strength of the components, the lubricants used, and the load on the bearing all play a role in determining how fast the bearing can go. To imagine this, think of a bearing rated the coveted ABEC 9. If this bearing carries a load of a 500 pound skater, it will perform differently than when loaded with a 100 pound skater. It will also perform differently with no skater at all.

THE ABEC RATING TELLS US ONLY ONE SMALL ASPECT ABOUT THE BEARINGS PERFORMANCE.

Additionally, if this ABEC 9 bearing is made from steel it will perform differently than if made from plastic. The ABEC rating tells us only one small aspect about the bearings performance.

ABEC Ratings were designed for industrial applications where bearings are being used in controlled environments. The actual measurements for ABEC tolerances are listed below. For scale, a human hair is roughly 0.180086mm thick.

• ABEC 1: 0.0075 mm (0.000295")
• ABEC 3: 0.0050 mm (0.000197")
• ABEC 5: 0.0035 mm (0.000138")
• ABEC 7: 0.0025 mm (0.000098")
• ABEC 9: 0.0012 mm (0.000047")

SO WHAT DOES THIS MEAN FOR SKATING?

One little tiny piece of dirt in your bearing, in the most technical sense, will completely void the ABEC Rating. When buying a bearing for a skate, they should be purchased with the knowledge that they degrade immediately when the bearing is placed in the harsh skating environment. Spending 2-4 times as much money for the ABEC 9 means you're spending cash on something that will almost immediately become void.

This being said, we are not telling you to go buy ABEC 1s. Higher ABEC Rated bearings usually use better quality of materials and lubes. These kinds of things matter a lot for how the bearing will perform over time in the environment of skating.

Higher ABECs often mean a better bearing because they also use better lubes, materials, etc. However, do not make the mistake that it is better because of the ABEC Rating alone. An ABEC 9 from Company X could be completely different than an ABEC 9 from Company Z.

It is also super common for bearing companies to lie about ABEC ratings. Getting the actual bearing tested is very expensive. The average skater won't do it. Hence, scummy companies just lie and get away with it.

Article taken from - https://stokedrideshop.com/blogs/ultimate-guides/the-ultimate-longboard-bearing-guide