The Halo ceramic series of bearings are a high quality steel/chrome bearing with metal shields and ceramic Si3N4 balls. These bearings have been tested and proven by many racers.
Bearing Dimensions
METRIC: 10mm (Inner) x 15mm (Outer) x 4mm (Width)
STANDARD: 0.3937" (Inner) x 0.59055" (Outer) x 0.15748" (Width)