Sprocket, walker & shoe drive
CTPA-AH115267 Replacement Part to Fit:  John Deere For Models: 6620 SN 610301-> 18 tooth 60 chain, 4.703"OD, 15 tooth 50 chain, 3.316"OD,19 ID spline  Price:  $48.30  Buyers Club Price:  $43.47