MTD Genuine Parts 13-Inch Caster Wheel for 50-Inch Zero Turn Mowers Caster wheel for 50" RZT mower Fits RZT mowers with 13"x5.00"-6" front wheels Hub Diameter .75". Axle diameter .75" Nylon bushing, grease fitting tubeless tire Replaces O.E. #634-04711-0911 and #634-04321A-0911