Three pieces of ¼ inch by 4” by 12” steel plate. One piece will be used to make four corner gussets and 1 will be used as mounting plates for the axles. You probably won’t need the other piece, but it’s always good to have a spare. About $18 each at Lowes. I thought that my 14” cut-off saw would zip through that ¼ inch steel plate, but no go. I ended up using one of my favorite toys, the angle grinder.