For smooth, accurate movement around curves and loops, these carriages have ball bearings that work well in high-speed, high-load applications. You'll often see these carriages and guide rails used to build assembly stations and other repetitive processes. Compared to roller and sleeve bearings, the ball bearings in these carriages operate with less friction, but they don't hold up as well as sleeve bearings in dusty and wet environments. The ball bearings don't have a cage, so they'll fall out if you remove the carriage from the guide rail.