This is the thin axle nut with right 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. Do not use if you chisel 1/2 way to threads! You should look at the threads to make sure they are not pulled. It is vital to have good threads!
Rear Hub Nut - RH - Spridget