A screw device for fixing insulating panels together is made in one piece from synthetic material and includes a head and a shank. The head has a flat surface for abutment on one of the insulating panels, a surface opposite the abutment surface having at least one drive wing, which extends to a distance greater than 10 mm from the opposite surface. The shank includes an elongate body extending from the head and substantially perpendicular to the abutment surface. The screw has a point arranged at an end of the body opposite the head, and at least one helical thread, which extends at least over part of at least one of the point and body, and is spaced from the head. The helical thread has a diameter that increases towards the head, a portion having a frustum-shaped envelope, and a pitch greater than 8 mm.