Originally Posted by bulgie

Unfortunately there's a shadow right across what looks like a notch. Am I imagining it or is there a notch? More pics please, that bike looks awesome!

If there's a notch then you can use something like this:

...the smaller end. I think the generic term is C-spanner or hook-spanner. You can get a set of 6 different sizes for under $20 if you don't mind cheap Chinese.

You probably won't find one with "Lock Ring" mis-spelled, those are rare and sought-after, but the one spelled right is commonplace or used to be.