The Ford Super Duty is a line of trucks (over 8,500 lb (3,900 kg) GVWR) introduced in 1998 for the 1999 model year. The F-250 to F-550 Super Duties are assembled at the Kentucky Truck Plant in Louisville, Kentucky. The F-650 and F-750 Super Duties are assembled at the Blue Diamond Truck plant in Mexico.
The Super Duty trucks are larger, heavier built series pickup trucks with heavier-duty body-on-frame steel ladder frames, axles, springs, brakes, transmissions, more powerful engines, and all other heavier/bigger components (with much higher payload and towing capacities) than the older traditional equivalent F-250, F-250HD (Heavy Duty), and F-350 Ford truck lines.
The two-wheel-drive and four-wheel-drive model frames are the same in the F-250 and F-350 series, making conversion from a two-wheel-drive model to a four-wheel-drive model less difficult than in other truck models. F-350 chassis cab, F-450 and F-550 frames are the same between the two-wheel-drive and four-wheel-drive models, and use the same suspension.
Source: Wikipedia 2012