The invention relates to a device comprising a first part (1) provided with a base (11) and a rod (12) having an opening or recess (13) for the engagement of an actuation tool (3), a second part (2) provided with a through-opening (21) for mounting on the rod (12) of the first part (1) and a surface for supporting the tool (3), as well as a tool (3) of the second part (2) along the rod (12) of the first part (1). The tool (3) comprises: a first arm (31) and a second arm (32) hinged on an intermediate shaft (33), having respective ends (31a, 32a) for acting on the first part (1) and the second part (2), and respective handles (31b and 32b); a mechanism (4) for positioning and regulating the rotational relative movement of the arms (31, 32).