This Solid Polyurethane Flat Free Tire is Perfect for Roofing Equipment, It comes Standard with a 3, 25 Centered Hub, Other Bearing Sizes Available, This product also comes with a grease zerk, 18x8, 508 Flat Free Tire with Ribbed Tread, Outside Tire Diameter: 17, 5, Tire Width: 8, 3, 1 Roller Bearing, SKU: MTNI032