These are the replacement Wheel Hub Ball Bearings for the Traxxas Nitro Revo Monster Truck. FEATURES Stainless Steel Construction Blue Rubber Sealed INCLUDES Two 12mm x 18mm Blue Sealed Stainless Wheel Hub Bearings REQUIREMENTS Assembly onto Vehicle SPECIFICATIONS Outer Diameter: 18mm (0.70") Inner Diameter: 12mm (0.47") Thickness: 4mm (0.15") COMMENTS These are for the Inside of the Wheel Hubs, the Truck Requires Four Total of these Bearings.