This is a very unique item for the outdoor deck, dock or patio life. With the Patented Universal Clamping System it can attach to the many different size and shape (round or square) upright balusters of a deck, dock, patio or fence. The clamp will adjust from a depth of 3/8 inch to 2 inches the width has a maximum of 2 1/8 inches. Using the same clamping system to securely hold the many different size pole accessories like Umbrellas, Shepherds Hooks, Garden Torches, Flagpoles and more. Note: Do not use with larger offset umbrellas. Ensure your railing or baluster can hold the additional weight.