Malone Auto Racks Kayak Stacker Foam Block Kit Accessory kit designed to transform Stax Pro into 2-boat carrier Pair of 8-inch foam stacker blocks protect kayak from crossbars Blocks hold kayak in place so it won't slip during loading and transport Includes two 12-foot tie-down straps along with bow & stern tie-down lines to secure boat to vehicle Allows Stax Pro to stack additional kayak weighing up to 80 pounds