Sealed Cartridge Steel Bearings

Grade 10 chromium steel balls. Round to within 10 millionths and twice as round as top of the line Dura Ace and Record loose balls.
High chromium steel bearing races.
High quality rubber seals that won't interfere with the balls themselves. The seals simply seal out contamination without increasing any rolling resistance.
High quality lithium grease. These bearings are acceptable replacements for any OEM bearing, already on your bike, they are economical and long lasting.