That clamp was the factory's fix for the hard-to-fasten top of the coupler. A friend of mine in MI found a TSB describing the fix for the top. He found both sizes (long and short), had them made up and sold them at the Nationals, other swap meets and on-line for a long time. When he couldn't get any more economically made, he sold his remaining stock to some other vendor at the Nationals. Apparently they disappeared for awhile then resurfaced - I've seen them on eBay. They do work!keeping the top on the coupler!