The standard license plate screw size for most vehicles in the United States is 1/4-14-3/4 inch. This size is a self-tapping screw that can fit most vehicles equipped with nylon or plastic screw retainers. However, some vehicles fitted with threaded metal holes use a different type of plate screw. The screw size is usually indicated on the mounting bracket or in the owners manual. It is important to use the correct size screw to ensure a secure fit and avoid damaging the vehicle.