The Well Stone -Molded "rock"is hollow to camouflage that water meter, septic head, or other intruder upon your beautiful landscape. Covers 18"well casings and 18"diameter sewage aerators. Incredibly realistic, with a patented bottom lip that has 4 pre-drilled holes for anchoring (disappears under mulch or soil). Thicker than others, and made with a super tough high density polyethylene that is UV treated.