The sizes that trailer hitch balls come in are 1 7/8 inches, 2 inches and 2 5/16 inches. Each ball size comes in varying shank diameters and lengths.
The 1 7/8-inch ball is used for towing 2,000 pounds or more, and it is used for small trailers. The 2-inch ball tows 3,500 to 8,000 pounds, and it is used to tow small to medium-size trailers. The 2 5/16-inch ball is for towing heavy-duty trailers that are 6,000 to 30,000 pounds.
The shank length of the ball is determined by the thickness of the drawbar. The type of hitch that is used determines which ball diameter is used.