Hillrider: You may be right about the ABEC numbering system. I just checked Enduro's site, and they show what I was calling ABEC3 as a "ZERO" bearing. What I was actually referring to is the ball grade: Grade 5 are 5/1000000"from being perfectly spherical. Grade 3 are 3/1000000" from it. The 'ZERO' bearing is then almost twice as smooth.