How do you attach the front nut on a carburettor?

Thanks a lot for all the brilliant advice. I finally managed to get it done last night. As Para says, the hardest part was getting the first turn on the tread. Not made any easier by the fact that for the first hour or so I was trying to turn it the wrong way. (Righty tighty lefty loosey but the damn thing is upside down...good learning experience all round)