If you don't want to read what I wrote but rather something more detailed and probably much easier to understand, go HERE and skip the next paragraph.

The ABEC bearing rating is a semi universal rating for almost all bearings. ABEC is used to rate besically any bearing from things like circular tools to some skateboard bearings. These are rated at high revolutions and skate bearings are not going to be going at extreme high speeds like a power drill. Skate-rated bearings are rated at lower speeds because they will never in normal use or expert use be going extremely fast as in revolutions. Skate rated bearings also rate different parts of the bearing and some of the parts in skate-rated bearings don't touch the balls like in ABEC rated bearings. Skate rated bearings are meant for skating and hard impacts from jumps and other things. Many people will tell you that they prefer skate-rated bearings over ABEC bearings.

I love my bones red bearings. They are skate-rated and run much smoother than the highest ABEC rated bearings that I have tried out. Sometime I hope to put in the cash for some Bones Swiss, but I'm not that serious.