In-ground Swimming Pool Cover Weight Blocks (20-Pack) NOT DESIGNED FOR ROUND OR ABOVE GROUND POOLS EASY TO USE. Simply place the Cover blocks around the edge of your pool cover, fill with water from your garden hose and snap on the top lid. MORE DURABLE: The hard plastic construction offers a longer lasting solution when compared to vinyl water bags, which may rupture or leak. STORE WITH EASE: The blocks nestle right inside each other making storage simple. MEASUREMENTS: Inner Dimensions: 36" L x 6" W x 4" H