I don't exactly know what they were originally for. I picked them up with the second load of free lumber. I suspect they made up some sort of shipping crate. most of the wood i got was originally large heavy duty crates for what looked to be large AC type units (sitting everywhere on the property)and pallets for moving steel around (I was told).
they are about 4.5' x 3' when open. and of course could be stacked to just about any height.
I keep thinking about using them for things like a
compost pile but I just hate that a job like that would mean they would quickly deteriorate. they look so damn useful just the way they are and I don't want to break them down to use the wood on something else.