Neoprene stopper that provides a mechanism to make it expandable. A tight fit will keep them from working their way out. 2 pcs 2 inch to 2-1/8 inch Neoprene Expansion Plug 50mm - 53mm Rubber Freeze Plug Replacement Rubber Expansion Plug/Rubber Freeze Plug/ Exhaust Pressure Test Plug Size: 2" to 2-1/8"(50mm - 53mm) Made Of High-Strength Neoprene Rubber & Steel It includes 2 pcs High Quality and Easy Installation