Telescopic metal closet rods are easy to install because they expand to fit any closet. Because the rods are hollow, they tend to sag if you hang too much on them.
One solution is to fill the core with a wooden dowel rod. The dowel should be smaller than the inside diameter of the metal rod and about one-quarter inch shorter than the width of the closet.
Unscrew the metal rod from the closet walls, insert the dowel and reinstall.