DescriptionSALE, 3 Month Warranty, Ceramic Lightning Ultra Seal Bike Bearing Kits are specially designed for on-road or relatively clean riding environments. The Ultra Seal is a non-contact, frictionless seal that is placed beneath a metal shield so they are still considered maintenance free and lubed for the life of the bearing. These bearings have ceramic balls, with stainless steel races and a C3 fit. Ceramic hybrids are lighter, capable of achieving higher RPM’s and sustaining higher operating temperatures than traditional bearings. Bearings that are packed in grease will require a short break in period to loosen up.