An adjustable elastic element (19) for forcing the surfaces of expandable-type anodes for diaphragm chlor-alkali cells wherein such element consists of a U-shaped elastic sheet provided with at least one adjusting mechanism comprising both one collar (29) which fastens the elastic sheet through openings obtained in the sheet itself and one gear (23) connectable to a removable external tool consisting of a handle and a shaft whereby turning the tool, a rotation of the gears is produced, in its turn acting on the collar controlling the span of the anode surfaces. And the span is freely adjustable in order to establish a predetermined controlled gap between anode and finger-supported diaphragm surfaces, or alternatively to bring such surfaces in contact without introducing however a useless and hazardous compression.