A hidden device for the wall assembly of a structural component of a piece of furniture or the like, comprising: - a body of the device - a movable hooking arm of said device having a free hook-shaped head 31, said movable arm being coupled with said body by means of at least a first regulation mechanism in depth and a second regulation mechanism in height so that said hook-shaped head protrudes from a first side of said body said first regulation mechanism in depth being at least suitable for causing the movement of the movable arm in a first substantially straight direction for moving the hook-shaped head towards/away from the body said second regulation mechanism in height being at least suitable for causing the movement of the movable arm in a second substantially angular direction, for moving the hook-shaped head over an arc of circumference, each of said regulation mechanisms (11,12) being provided with respective screw-control elements (13,14) that can be activated by a tool for respectively determining the movement of the arm in the first and/or second direction, said control elements (13,14) comprising shaped engagement means (15,16) for said tool wherein for each screw-control element (13,14), the shaped engagement means (15,16) can be at least radially engaged with respect to the axis of the screw, so that they can be activated from opposite sides of the body, wherein the screw-control elements (13,14) are provided with at least one driving head, said shaped engagement means (15,16) being located on said driving head, wherein the driving head is provided with a toothed crown suitable for forming at least the shaped engagement means (15,16) for the tool, so that the toothed crown can be radially engaged, with respect to a longitudinal development axis of the screw, by said tool, characterized in that at least one of the screw elements comprises an engagement imprint for the tool, wherein said toothed crown of said at least one of the screw elements is provided substantially around said imprint, said imprint being located on the head so as to be axially engaged by the tool. - a body of the device - a movable hooking arm of said device having a free hook-shaped head 31, said movable arm being coupled with said body by means of at least a first regulation mechanism in depth and a second regulation mechanism in height so that said hook-shaped head protrudes from a first side of said body said first regulation mechanism in depth being at least suitable for causing the movement of the movable arm in a first substantially straight direction for moving the hook-shaped head towards/away from the body said second regulation mechanism in height being at least suitable for causing the movement of the movable arm in a second substantially angular direction, for moving the hook-shaped head over an arc of circumference, each of said regulation mechanisms (11,12) being provided with respective screw-control elements (13,14) that can be activated by a tool for respectively determining the movement of the arm in the first and/or second direction, said control elements (13,14) comprising shaped engagement means (15,16) for said tool wherein for each screw-control element (13,14), the shaped engagement means (15,16) can be at least radially engaged with respect to the axis of the screw, so that they can be activated from opposite sides of the body, wherein the screw-control elements (13,14) are provided with at least one driving head, said shaped engagement means (15,16) being located on said driving head, wherein the driving head is provided with a toothed crown suitable for forming at least the shaped engagement means (15,16) for the tool, so that the toothed crown can be radially engaged, with respect to a longitudinal development axis of the screw, by said tool, characterized in that at least one of the screw elements comprises an engagement imprint for the tool, wherein said toothed crown of said at least one of the screw elements is provided substantially around said imprint, said imprint being located on the head so as to be axially engaged by the tool.