Smooth rolling guides assist in centering the boat onto the trailer. Ideal for retrieving boat on shallow ramps where the trailer is not far into the water, when alone, or have a crosswind or current pushing the boat. Uprights with rollers come fully assembled, ready for installation. Sold in pairs. 1-1/2" Pre-galvanized steel uprights lean outward 15° to cradle the boatGuide-Ons are 21" tall above the frame with 9" roller & 2" roller caps at top & bottomMounting hardware included for frames up to 3" W x 4-1/4"HMouting brackets allow up to 13" of adjustment out from each side of the frame