I have an inherited 1997 Fuji Odessa MTB. I'm trying to replace the rear cogs (7-speed) and went to remove the (what I believe to be a cassette) then noticed there's no lock ring. Strange, even though the visible ring says LOCK. It says Sun Race on it. I have the Park FR-5 which only fits on the way inner splines that dosnt rotate. Here's what it looks like



Am I missing something or is there really no lock ring on there? How do I get this cassette off? Or is it a freewheel? Help Appreciated. Thanks.