From which width onwards must truck tractors be equipped with these warning plates?

You answered correctly. In Germany, truck tractors (and similar agricultural vehicles) must be equipped with red and white warning plates if their width exceeds 2.75 meters. This rule helps to warn other road users about the unusually wide vehicle to increase road safety, especially on narrow roads or at night. Remember: wider vehicles are harder to see and judge, so clear warning markings are mandatory from this width onwards. Whenever you encounter similar questions, always check if the width is more than 2.75 meters—this is the key threshold for requiring warning plates according to German regulations.