I'm wondering what to look for in buying ball bearings (wheel bearings, transmission, etc.) if you know the 4 digit number and want top quality bearings. I see most listings describe them as "electric motor grade". Are there different grades that are listed with the same 4 digit number? I know the seals add a few letters to the number. THAT I can figure out. I see a HUGE difference in price from top to bottom. Is it worth the premium? Should I stick with US manufacturers? They would be easier to find for me although I certainly think Japanese bearings are good quality. Not too sure about Chinese bearings, though. Any advice for me?