Product Description: Our trailer balls are engineered to the highest quality in consistency, accuracy, fit, and strength. They have a quality finish and fine threads for more holding strength. They all meet the U.S. V-5specifications and are tested for your safety. Many elements determine the correct trailer ball; mounting platform thickness, hole size, couplersize, gross trailer weight rating. The platform must be at least 3/8" thick and the hole size mustnot be more than 1/16" larger in diameter than the shank.