Most domestic-branded pickups are offered in more configurations than any normal human can count.
All F-250 models come with single rear wheels. F-350 models are available with single rear wheels (SRW) or dual rear wheels (DRW). The latter, often referred to as "dualies," are beneficial for towing as they offer higher tongue weight ratings.
Ford Super Duty F-250 competes with the other heavyweights from Detroit: Dodge Ram 2500, Chevrolet Silverado 2500 and GMC Sierra 2500. F-350 dual rear wheel models compete with the 3500-series models from GM and Dodge.