What a great site this is; I get advice from the Pacific seaboard and somebody else can put me in touch with someone in my own smallish town!
Well, things do look bog simple under that ring. There's a split in the thread which I presume closes slightly as the lockring travels downwards, thereby clamping the (steering?) tube. Is this arrangement restricted to cheap-end bikes?
The lockring is at least 4mm thick but there appears to be a thinner ring underneath it, this time with no notches. Am I supposed to unscrew that too?