two ball bearings that are perfectly aligned and extremely compact. That means that it will keep going for longer period of time and with lesser friction. Single bearings with just one ball will spin for less time, and is not as efficient as a larger bearing.

Bearings are designed to reduce vibration and motion, while also taking on the load put upon them. Bearings are used to reduce friction and heat. This video talks about three types of bearings, which use bronze bushings, as well as steel ball bearings. s4uhh8zh43.