The Mk2 Panda (169) rear wheel bearing comes complete with hub and retaining nut. I think it might have a 32mm retaining nut but really can't remember. However, the kit is about £30 and you can measure the nut that comes with it.
When you do the job, don't lose the thick washer or back spacer sleeve (if there is one) as that does not come with the new hub.