Trailer balls have four key measurements: ball diameter, shank length, shank diameter and rise.
The ball diameter is the diameter of the trailer ball sphere itself. The shank length is the total distance of the threaded stem. The shank diameter is the diameter of the threaded stem, and the rise is how high the trailer ball sits off of its base.
The size of the trailer ball needed for your towing setup will be determined by three things: your coupler size, trailer ball hole diameter and your towing capacity.
In short, your trailer ball diameter must match your coupler size, the shank diameter must fit the ball hole and the weight capacity must be enough to safely tow your trailer.
Step 1: Match the Ball to the Coupler Size
When choosing a trailer ball, first select the ball diameter by matching it to the coupler size. Most manufacturers stamp or label the correct trailer ball size on the coupler.
Make sure that your coupler and trailer ball have a solid connection before towing and that all necessary adjustments have been made.
Step 2: Match the Shank to the Trailer Ball Hole
The hole in the platform of a ball mount or bumper hitch is where the trailer ball bolts onto. It is important to know the diameter of this hole so that you can choose a trailer ball with a matching shank diameter.
If the trailer ball shank is too small, it will shift while towing and likely come loose. If the shank size is too small for the trailer ball hole, you may be able to use a reducer bushing to make up the difference.
Step 3: Match the Weight Capacity of Your Towing
When selecting a trailer ball or any towing accessory, weight capacity must always be considered. The weight rating for a trailer ball will be listed as the ball capacity. Note that this will reflect the gross trailer weight limit, not the tongue weight.
You must select a trailer ball with a ball capacity that exceeds the gross weight of your trailer.
How to Choose a Trailer Ball Video
Most Common Trailer Ball Size
Perhaps the most common hitch ball size is the 2-inch ball. This is because 2-inch trailer balls are the best fit for most class 3 hitches, and class 3 hitches are the most popular trailer hitch.
Despite this fact, each towing setup is different, and there is no one-size-fits-all, universal trailer ball. For your own towing setup, make sure you choose the ball the best fits your coupler, ball mount and weight requirements.
Travel Trailer Hitch Ball Size
The hitch ball used to tow most travel trailers is a 2-inch or 2-5/16-inch trailer ball. Travel trailers can weigh anywhere from 5,000 to 10,000 lbs. or more, and the 2-inch to 2-5/16-inch ball weight ratings provide a perfect match.
Additionally, many travel trailers are pulled using a weight distribution hitch. Most WD hitches come standard with a 2-5/16-inch ball.