36mm nut to approx. 240 ft lbs. ...use a new cotter pin.
If you don't have a torque wrench 200 lbs of body weight 2' out on a piece of pipe will suffice.
The reason for the 240 lb torque is that the stub axle is hardened steel compared to the softer rotor or drum. If there is the slightest play the rotor splines they will shear or wear away.