I am not quite clear how I acquired the medium spools that I offered to the children for their play. Did I dumpster dive at a construction site or did a parent bring them in? I do not know. I do know they are the kind of spools that hold the wire that electricians use.
In the picture below, two children found another use for the spools. They placed their cars on the core of the spools to create monster trucks with giant wheels rolling down the slide.