Things to know about ABEC ratings:

1. Bearings not conforming to at least ABEC 1 can not be classified as precision bearings as their tolerances are too loose.
2. Lower ABEC grades are intended for applications such as mechanical hobbies, skates, skateboards, fishing reels, and alike.
3. Mid-range grades (ABEC 5) are intended for applications such as vehicles, electric motors and industrial machinery. The maximum allowable tolerance on these bearings is 0.0035 mm.
4. High grade bearings are intended for precision applications like aircraft instruments, jet engines, or surgical equipment. These can often cost many hundreds of dollars each. As a side note, the supplier I use has also sold to NASA. The highest precision bearing they have sold to date was for the international space station and cost $128,000. It was 8 feet in diameter and was an ABEC grade 9.