Hydraulic pump drive gear (this is the larger 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