The built-in cup shape at buoy's top, courtesy of the rope-nest design, allows the anchor shackle to nest below buoy's surface. This recessed area helps shield the shackle from contacting the boat hull while also providing a convenient nesting place for the pennant line when your boat departs from the mooring. The hard-skin polyethylene shell is UV-protected to resist weathering effects of sunlight and is foam-filled to positively displace water. A sandblasted finish on the hard-skin shell allows the buoy to be easily painted for identification. Tube-through-center design with blue reflective striping. 21⁄2" tube dia., 18" buoy dia. 100-lb. approximate buoyancy. Hardware not included.