Thanks
You are right , there are 4 pieces of aluminum extrusion , 80mm x 80mm ,
heavy , made by ITEM . They are hold together by those aluminum plates ,
( 1 in front , 2 at sides , 1 on top ) wich are bolted to each other too...
Plus , the extrusions are conected with the base ... There are some pics of
the structure around here , take a look there ...