Cap Screw
CTPA-R26804 Replacement Part to Fit:  John Deere For Models: 2520, 3010, 3020, 4000, 4010, 4020, 500C, JD500, JD500A, JD500B, JD600 S/N <202237 Not Req on tractors Less PTO.  Price:  $8.76  Buyers Club Price:  $7.88