ABEC – Annular Bearing Engineers Committee 

When trying to figure out what bearings to use, you will likely come across an ABEC number.  Bearings come in 5 levels of precision, 1, 3, 5, 7, and 9.  The lower end has looser tolerances and the higher end has tighter tolerances.  Tighter tolerances should allow bearings to freely spin easier, and they should last longer as you spin them.  If you see a ABEC 11 or 13, they are not real.  The official scale only goes to 9.  

More about ABEC Tolerances.