The line width override applied to the transition.
Setting the value to 0 removes the width override on the transition, so the transition reverts to the default thickness. On a state-to-state transition, this property sets the width of the transition's wire and of the border of its arrow. On a self transition, this property sets the width of the transition arrow's border.
ITransition startTransition = myStateMachine.GetTransitions(startState, nextState).First(); startTransition.WidthOverride = 4f;