Shimano Stradic 4000FG

My Shimano spinning reel schematic shows a rubber friction ring. Mine was missing so I bought one and there is no way it will fit on my reel so I left it off. What is the purpose of this ring? Why would the spool need friction? Thanks.

I'm assuming it fits on the front of the spool under the hand tighten nut? If so its for the drag.
As you tighten it. It creates friction against the spool causing it to slip less or lossened for more slip. You don't want it tighter then the weight line your using. You want it to slip before the line breaks off on say a fish. Or say you set the hook in a stump it prevents the rod being broken.
Usually there Teflon looking material and not rubber. Hum might have a rubber one stacked in there come to think of it.
Are we on the same page or are you talking about another reel part?

It's an O-ring about 2" in diameter that fits on the main body of the reel. The spool slips over it sealing the bottom of the spool, but it causes a lot of drag. It's not the drag adjustment on the front of the spool.

how do you like you shimano? other than this o-ring thing.

I have a 5000 and a 6000 and they are great reels.