Curtain side box trucks are prevalent in Europe and are close cousins to small flatbed delivery trucks commonly seen in most US cities. A main difference, however, is how the superstructure is buttressed by the tie downs used inside. In these images we see common, 'unrateable' lumber added as structure, which if used to support the side curtain is probably fine but if counted on for cargo control is guess-work, at best! These spring clamps are not able to be measured outside of a laboratory and the strength of the lumber varies specie to specie, milled piece to milled piece (better hope there are no knots!). The weight of the end piece castings alone is enough to place a measurable strain on the lumber, even before freight has been loaded onto the bed. These pictured products do not exist in the US, the superstructure of the sliding tarp mechanism is not used for tie down anchor points. However, in the US, Nurseries and similar industries that transport lightweight carts filled with products do rely on Wood Beam Sockets, metal end clamps that hold each end of 2x6 or 2x4 pre-cut lumber and rest in E-Track slots. The key is that the product being transported is lightweight and the lumber is not used as support for the box structure.
