Single precision bearing helps the wheel roll mute & smoothly. The caster can rotate at ease, thanks to it's double bearing raceways. Plastic bearing hubs help prevent dust and silk intrude inside the core - thus increase its lifetime.
Wheel surface hardness is Shore A: 95±2 so the wheel can help reduce noise when operating. Plastic hubs helps reduce dust, water, silk goes into its Single precision bearing. Thus longer caster's lifetime with less maintenance.