Loose hub nut

When my GE washing machine goes into spin cycle the tub will come out of balance and the machine sounds like it’s about to come out of the closet. I’ve narrowed it down to a loose hub nut. Does this nut go in with the flat side facing up or down? Also, what is the correct tool for the job? I found a Spanner Nut Wrench on another site but I’m not sure it’s the correct tool. They don’t seem to sell it on this site and the forums don’t seem to allow me to link to another site.

Also, what can I use to keep the hub nut from coming loose in the future?

If the hub nut is really loose, make sure the spin basket is not damaged, if so you will need a new spin basket and you can order the spanner wrench, part # WX5X1325, this hub nut has left hand threads.