Product review (5 stars): I also didn't buy the specialized gasket tools and while the outer retaining ring is pretty easy to get on and off
It is a gasket to keep water on inside, and works.  I also didn't buy the specialized gasket tools and while the outer retaining ring is pretty easy to get on and off, the inside one is a bear.  It would have been a bit easier if I had actually taken the washer apart, but I've done that a couple of times and thought I'd save time.  I was wrong about that.

One trick I finally stumbled upon after trying about every tool I had to try to get the inner retaining ring on was to take some baling wire I had laying around.  I looped it around the spring and the loop in the piece of metal that attaches to the spring.  Then taking a pair of lineman pliers, I twisted the ends of the baling wire over and over to expand the spring until I had enough room to slide the hook through it.  Once I hit upon this trick, it was a quick process.