The invention relates to a screw device (1) for fixing insulating panels together. The screw (1) is made in one piece from synthetic material and comprises a head (2) and a shank (3). The head (2) comprises a flat surface (4) for abutment on one of the said insulating panels, a surface (5) opposite the abutment surface (4), provided with at least one drive wing (6). The wing (6) extends to a selected distance A from the opposite surface (5), said distance A being more than 10 mm. The shank (3) comprises an elongate body (7) extending from the head (2) and substantially perpendicular to the abutment surface (4). The screw (1) comprises a point (8) arranged at an end of the body (7) opposite the head (2), and at least one helical thread (9). The helical thread 9 extends at least over part of at least one of the point (8) and the body (7), and is spaced from the head (2). The helical thread (9) has a diameter (H) that increases towards the head (2), the helical thread (9) comprising a portion having a frustum-shaped envelope (18), the pitch (P) of the helical thread (9) being greater than 8 mm.