It’s an old classification for trucks that aren’t used anymore. 1/2 ton = 150/1500 3/4 ton = 250/2500 1 ton = 350/3500 It’s the weight they can carry, not the weight of the truck. I have a 3500 Ram diesel, it’s a 1 ton truck, but it weighs like 8 or 9000 lbs. Just the engine is about half a ton.