2013 Toyota 4Runner Owners Manual - Page 604

2-5. Driving information Selecting trailer ball Use the correct trailer ball for your application. Trailer ball load rating Matches or exceeds the gross trailer weight rating of the trailer. Ball diameter Matches the size of the trailer coupler. Most couplers are stamped with the required trailer ball size. Trailer class IV II and III I Typical trailer ball size 2 5/16 in. 2 in. 1 7/8 in. 2 When driving Shank length Protrudes beyond the bottom of the lock washer and nut by at least 2 threads. Shank diameter Matches the ball mount hole diameter size. 303 4RUNNER_U