"End-Caps" are designed to fit on either the top or bottom of the 2" x 4" posts that are commonly used to support shrinkwrap covers.
They are made of high density polyethylene for durability and ease of use.
Used as a top cap, they provide a large supportive surface area and have slits every 90° for the woven cord shrinkwrap support strapping to slide into.
When the cover is shrunk, the four corner sections flex downward forming a protective pad on the top of the post to eliminate it poking through.
If you choose not to use the purpose designed non-skid Bottom Caps, you can also use End-Caps on the bottom ends of the 2 x 4 posts. They help hold the post upright and pad the end to keep it from scratching the deck.