You have to be really careful not to overtighten them. It is very easy to strip the thread on the axle.
In fact, the whole drivetrain of a Justy seems to be made of rather soft stuff.
We had a problem where, under acceleration with 4WD engaged, the back of the car would occasionally swing out sideways without warning. It was rather scary.
I eventually found that the splines had worn away on one the rear hubs such that the axle would spin inside it, when given enough torque to overcome the friction.
Phil.