Hydraulic pump drive gear (this is the smaller of the two gears).
Ford hydraulic pumps on Ford tractors: 2000 (3 cylinder) 3000, 4000 (3 cylinder), 4000SU, 2600, 3600, 4600, 4600SU, 2310, 2610, 2810, 2910, 3610, 3910, 4610SU, 231, 335, 531, 340, 540, 3400, 3500, 445, 4500, 340, 340A, 340B, 445, 445A, 531, 542, 540, 540A