There are actually two nuts, with a lock washer in between them. Bend the locking tab out of the slot with a small chisel or a narrow screwdriver, and use a hammer and a flat-tipped punch (not a chisel) and a hammer to back the nut off. Then remove the washer and remove the second nut the same way. On reinstallation, use the inner nut to set the preload on the wheel bearing while rotating the wheel and hub assembly. Don't overtighten it- - - -just take up the play in the bearings, then bend a lock tab into one of the slots on the inner nut to retain the bearing adjustment. Tighten the outer nut securely and bend another lock tab out to keep it from loosening.
Be aware that if those nuts back off the entire hub and axle assembly can part company with the vehicle- - - -I've recovered a few disabled big rigs and had to go searching down the side of the road for a missing hub, tire and axle assembly!
Jerry
