This is the thin axle nut with left hand threads. It is on with about 100 lbs. of torque. If you do not have a socket [not many do] to remove you can use a chisel to remove. Make sure you remove this in the opposite direction than the right hand nut. Do not use if you chisel 1/2 way to threads! I have talked with people that did remove this LH nut in the RH manner, they had to replace the rear axle housing You should look at the threads to make sure they are not pulled. It is vital to have good threads!
Rear Hub Nut- LH - Spridget