I'M NOT SURE IF THEY MAKE THESE THAT SMALL; HOWEVER, ONE COULD POSSIBLY TAKE THE CENTER ROD OUT, CUT IT AND THE SPRING TO THE DESIRED LENGTH AND REASSEMBLE THE ROD.
this is a tension (or pressure fit ) rod. Unscrew the thin end (counterclockwise) until it is over sized for the space it will fill. The spring inside the rod will compact as you put it between the window framework verticals and re- expand to exert pressure against the window framework. Just place the large non twisting end against the frame first, then compress the narrow end to squeeze it in place on the other side. The internal spring provides tension between the two points and the rod stays in place. If the rod falls out out the window opening you have not started with the rod oversized enough to produce enough pressure. Unscrew the thin end more and try again. If it keeps falling out it would only be because the curtains you are hanging are simply too heavy for a tension rod. Spring tension rods are predominantly used for sheers or cafe sets as opposed to heavy draperies or multi-layered valances.
Have you tried a local hardware store? If not there, you might need to buy one rod to get replacement ends.
The shorter the rod, the smaller the caps.
These are made to hold sheers only.
THAT DEPENDS ON WHERE YOU PLACE IT. IF IT'S EXPOSED TO HUMID DAMP CONDITIONS IT WILL OVER TIME OXIDIZE. I'VE HAD A SMALLER ROD SOMEWHAT SIMILAR TO THIS ONE IN MY MASTER BATHROOM FOR OVER 32 YEARS AND IT'S STILL LIKE NEW.
That's super long for a tension rod! It likely won't stay up once you hang material on it. Sounds like you should go with a pole rod with round clip rings to hold the material.