I made my own out of a piece of thick wall square tubing by cutting it so that I have one wall and two corners resulting in a shallow and wide "U" section. I used a square shaped "U" bolt for holding axles to leaf springs to clamp it to the hitch. Has worked great for many years. It is similar to this device except I didn't have to weld on a rod for the second end.
http://www.princessauto.com/en/detail/anti-rattle-hitch-receiver-immobilizer/A-p8465957e
Most of these type of anti rattle clamps are shown raising the ball mount UP to take out the slack. I clamp mine DOWN in it's natural position, seems like a better way to do it to me.
