Sprocket, walker & shoe drive
CTPA-AH87249 Replacement Part to Fit:  John Deere For Models: 6600 sn 105801->, 7700 sn 111901-> 15 & 15 tooth 50 chain, 3.316" OD, 1.127" ID  Price:  $36.54  Buyers Club Price:  $32.89