New Genuine Ariens Gravely LM 21 S, LM 21 SE, LM 21 SC 21” Self-Propelled Walk Behind Mower Drive System .500X.688X.625 Needle Bearing #05415300 Replaces #54153. Comes in Idler Gear Assembly #51101200 Replaces #61101600 #511012 #611016.