The invention is characterized by the connection between the plates (3 and/or 5) and the bars (1 and 2) which have narrowed or reduced section extremities; the extremities are provided with anchoring notches such as cottering, threading, saw teeth and the like, which are similar to those provided in the orifices of the plates (3 and 5), as well as means for fixing or connecting the gratings or bars to the wall, said means consisting of squares of which one of the wings (12) has back-folded extremities (13) while the other wing (10) has a hole (11).