These hooks took about 20 minutes to design in OpenSCAD and were made so that the project could get off the ground immediately - students were eager to get started.
I knew the tracks would take a while to design - print - redesign etc so I designed these hooks for use with 3/4'' PVC pipe (we happened to have about 30 ft of this sitting around). The design is easily adaptable to other sizes of PVC.
These were designed to also work with magnets (1/2") to be used on a magnetic blackboard instead.
At sharp angles the PVC will slide since their is no lip on the hooks. A piece of tape takes care of that pretty well.
As a side note, these are useful as simply hooks for hanging cables and other things as necessary.