Grade-5 ceramic (Silicon Nitride: Si3N4) balls with graphite-polyamide retainers in a metal-race carrier/shell. LLB seal is a light-contact, two lip seal that rides in a groove. Packed with Super Web RR-1 grease. Features: All measurements are in millimeters Grade 5 ball bearings with Polyamide retainers Very light contact type, perfect for high performance hubs 2 lip seals minimize bearing contamination