My 3D printer is set up in the closet of my office. All of the shelves are filled with stuff, but the closet rod is completely unused. I've seen a few designs people created to store filament hanging from closet rods but I wasn't a fan of them.

This is designed to use 2 pieces of 1"(25mm) PVC which has an O.D. of 1.315" (33.4mm). The fit is very slightly loose because I found PVC to not be perfectly round. A dab of hot glue keeps everything secure, but isn't completely necessary.

The hook piece dovetails into one of the 2 support types and is a friction fit. Depending on the length of PVC you use, more of the middle supports may be necessary (or none at all).