Black and Decker router HD1250 - tightening cutter ??

[davej.]

Hi , just tried changing the cutter in a newly acquired Black and Decker router HD1250 but there seems to me that there is an "extra" nut - the larger but thinner one in the middle. I'm guessing that is a lock nut for after the cutter is tightened and is tightened up to the top nut ?
I'd be grateful if someone could confirm - cheers in advance.
Dave.j