Probably what you are talking about is the tapering piece is the CO2 check valve shown as #10 in the following link.
The 3 fin jobber is the check ball retainer shown as #1 in the same link.
Be sure to dissasemble your keg coupler completely before cleaning.
I put all the little parts in a small plastic or nylon mesh bag like fruits & vegetables come in from the grocery store. This makes it harder to lose or pour down the drain accidently. (Don't ask me how I came up with this trick.)
http://www.micromatic.com/draft-keg-...pid-7485E.html