I got the Zenna Home Adjustable Tension Shower rod. It adjusts from 26 to 76 inches. When it came out of the box it was in three seperste pieces and I instantly started to get nervous as there were these plastic caps on one of the pieces. Like most people, I just didnt think I had to read the instructions. I tried to put the three rods together and it did not fit. I took the caps off and bam! The middle rod fit in perfect! It tightens like it should and adjusts just right. 
The one thing I did find is that there is a white plastic piece inside and it accidently fell out when I was messing around with it. But luckily it did go back in and works just fine.