This was the most messed up thing on the printer - it started out looking like this:

and wound up looking like this:

at the base, and:

at the top, where the belt idler is.  Note that the body is printed, with a pulley, skateboard bearings and central ground steel shaft.  The belt is a pretty standard 6mm GT2.  Here's an exploded view:

On the axis slider is a printed adapter that fits over the original wire termination:

Note that the top flag is for the optical Z-stop.

This made a huge difference to the reliability of the printer - at the time of this writing it's been running almost continuously for days churning out large chess pieces.  :)