Poly box truck is molded in heavy duty polyethylene. The molded vertical ribs for medium sized boxes provides rigidity and strength. Smaller models do not need that vertical rib. The boxes are secured to an all welded angle iron dolly by bolting through the bodies. Lids are optional for 7 of these products: the 8, 10, 12, 14, 16, 18, and 20 bushel unit. The 8 bushel capacity can hold 400 pounds, the 10, 12, and 14 bushel capacity can hold 600 pounds, and the rest can hold 800 pounds. Casters are 5" for all models except the 8 bushel capacity model. The 8 bushel capacity has a caster size of 3 inches. Dimension listed is overall, so subtract 6.5" for body depth. For the 8 bushel version subtract 4" for body depth.