21 Round Heavy Duty 10 Year pool cover. This solid winter cover is designed to fit 21 ft round above ground pools. Cover is triple laminated polyethylene and features an 8 x 8 scrim count. This cover is Blue on the top side and the Black underside helps to prevent algae growth. Also included is a vinyl coated steel cable along with a non-rusting deluxe aluminum cable winch for secure lock down. 2 non-rusting aluminum grommets every 3 feet around entire cover's perimeter for added strength and security. Each cover comes with a 4 ft of overlap and the actual cover size measures approx. 25 ft. This overlap allows the cover to wrap up under the pool top rails for secure attachment. 10 Year warranty with 1 year full rated.