No more air and water infiltration. Endura Z-Series Adjustable Inswing Cap Sill System Product details: Cap plugs cover and protect the adjustment screws, ensuring durability of the screws. Continuous substrate surface that can be cut down to meet your opening. Easy cap adjustment to form a proper seal against the bottom of the door for optimal sealing. Why buy Endura Z-Series Adjustable Sill? The Z-Series uses a patented design of all synthetic components that eliminates the worries of wood substrate sills. Built to last, the advanced all-composite substrate and streamlined synthetic cap means no rotting, warping or deterioration over time. Screw covers keep debris out for easy adjustment anytime, and prevent exposure to unsightly rusted screws.