This convenient small adapter allows the user to mount an additional disc or other tripod accessories in place of the retractile hook assembly at the bottom of the column. It works only for the new generation of tripods that feature the Ground Level Set. In these tripods, the hook assembly is fixed by a M12 thread, and thus this 3/8'' adapter is needed in order to attach any other standard accessory. This adapter is not necessary and it would not work for the previous generation of tripods without ground level. These older tripods already have at the bottom of the column a 3/8'' thread.