Dock Edge 18 inch Dock Wheel. Here's the description from the Harbour Chandler website (www.harbourchandler.ca): Smooth rolling wheel offers substantial dock cushioning and features molded-in valves to adjust the level of firmness. Heavy-duty hot dipped galvanized hardware mounts securely to the dock and has a broad base for corner mounting to give it extra strength. Guides boat into your slip [or boathouse] easily, regardless of wind and current conditions. Integrally molded ribs both top and bottom of this wheel makes it valuable dock and boat protection and a formidable guard against impacts. Dimensions: 18 inch diameter, 7 inch wheel height. 90 degree galvanized bracket has 8 inch arms.