a few points here
The rings are different, the top one has a 'keystone' profile section (it's thinner on the inside circumference than the outside circumference...this on goes into the top groove
The other ring is flat in Its profile section, this one goes into the bottom groove but first put in the little springy thing so that the ends are either side of the locating peg
You'll notice that the rings have a shape ground into the ends so that they fit correctly around the locating pegs