This Reese sway control adapter bracket is for Class III and IV two-inch square ball mounts. Simply remove hitch ball, place adapter bracket on ball shank and reinstall hitch ball. Bracket is reversible for use on road or curbside of trailer. The ball mount platform must be 2-1/2" wide and have a 1" ball hole. The adapter is made of 3/8" thick material and mounts under the hitch ball. When installed, the shank length of the hitch ball must be long enough to allow at least two threads to be visible when the hitch ball is installed and the nut is completely tightened. A hitch ball with an extra long shank may be required.