They have a bearing that allow smooth rotation and speed. (ptinto.com)
Each model is made of stainless steel and equipped with solid R188 high - speed bearings in the center to ensure smooth rotation and maximum speed. (geekwrapped.com)
If I could end on a sweet note, that volume knob was a nice one, with smooth rotation and linear changes in volume level regardless of how quickly I twisted it about. (cnet.com)