Most travel trailers, but not all, can be towed with a 2-inch or 2 5/16-inch diameter trailer ball. The size of the trailer ball for your towing configuration is based on your vehicle’s towing capacity, your coupler size, and the trailer ball hole diameter. Your trailer ball diameter must match your coupler size, the shank diameter must match the trailer ball hole and the weight capacity must be enough to tow your trailer.