revolvo;

It's unlikely that it will seperate, but you do want to tighten that nut. Use a special wrench for that...I believe that's where the term SPANNER wrench in British English comes from...you could make one up it you had access to a band saw...it's essentially a half circle arc which spans the shaft, with a handle on one side and a pin which picks up one of those holes on the other (I expect a quick search would get you a pic)...or you can use one of those band wrenches (Plumbers tool) as other poster suggests....a pipe wrench alone would bung up the nut pretty good, but would work fine at that, if the nut was protected with a thick piece of leather!...I'd loosen it first, wirebrush the threads, lube, then retighten.

Cheers