PRECISION 608 2RU BEARINGS, FAST Precision honed races & balls, STRONG Deep groove raceways and premium SUJ2 chrome steel withstand hardest turns and stops, LONG LASTING Labyrinth seal defends against dirt & debris to extend bearing life, SMOOTH Nylon ball retainer – lighter, quieter and faster than a metal cage, SERVICEABLE Pre-lubricated with Sonic Super Gel – remove non-contact rubber seals for easy cleaning