Small springs on truck frame rails

Truck experts:
AFV Club’s kits of the M35/M49 and M54 trucks show small rods with springs going around them on the outside of the frame rails - at least that’s what they turn out to be in pictures of the prototypes, near the middle of the rails.
Now what are these things for? They evidently are connected to the respective load beds, but I don’t believe that they might influence the softness of the ride for the cargo. Please enlighten me!

The spring acts the same as a lock washer, just with more pressure. They keep pressure on the nut so it can not come loose from vibration and work its way off. They are pretty much a safety feature to ensure the bed/loadbox stays on securely.

Thank you very much, Gino ‐ just four nuts, but secured like that? Sounds like swathing flies with a sledge hammer! Anyway, a case for very fine wire, as discussed elsewhere.