BALLMOUNT - Class I and II hitches come with a ball mount which is selected at the factory. However, class III-IV are used to tow a variety of trailer sizes. Therefore, a calculation is made to determine the correct ball mount based on the height of your trailer in a level towing position. There are more than 25 different sizes and finishes to choose from! Your authorized Hidden Hitch dealer can Help. If you don't see the hitch or towing accessory that you are looking for, give us a call toll free at 1-866-820-2153.