Introducing the 20" Mounting Rail and Planter Box Brackets! This system is designed to hold any planter box up to 36" long and 6 1/2" or less wide at the bottom - which is most. As all Hold It Mate mounting rails go - they fit universally on vertical spindles/fences. Round, square, wood, wrought iron aluminum, 1/2" to 1 1/2" deep, fits them all! The mounting rails and hardware basically disappear behind your planters - so your plantings appear to be floating - its a beautiful look, giving focus on the plants and planters, not the hardware.