I'm working on a project where I want two separate shafts to be in the same place. Think of it like a clock where the hour and minute hands move independently. Also like a clock, I want the motors and gears tucked away in back.
With clocks, they use a kind of tube that slides over a shaft. Then the shaft and the tube can both be driven from the back and rotate independently.
Is there a name for this tube part? If I wanted it to be low-friction, is there a name for a part that includes bearings?