One for anyone who's lost the bearing retaining nut for their CB400/500/550 (not me, of course - I never lose anything... ahemm...)
Getting an OEM replacement can be a pain, but the stem nut from a cr or crm 125/250/450 fits nicely. Stem nut for a Husqvarna WR125, TC250 or SM250R is the same thread so should fit too.