This adapter bracket has been made to accommodate the popular Volisun solar post cap lights sold on a major online e-tailers site. The Volisun solar lights contain four different sizes of post caps, but none of them work with a Trex post sleeve cover, a very popular element in composite deck building. This adapter fits over a standard 4.5" x 4.5" post sleeve, and allows the solar light to twist lock in place, just like the caps which come with the solar lights. It also contains four screw holes to secure the bracket to the wooden 4" x 4" post contained in the post sleeve.