Reinforced ribbed washers, ideal for laying insulation panels and mechanically fixing bituminous membranes and synthetic waterproofing felts made of PVC, TPO and TPE. They offer increased rigidity and durability. They are used for the installation of insulation panels and for the mechanical fixing of bituminous membranes and synthetic waterproofing felts made of PVC, TPO and TPE. The washers are equipped with ribs to increase stiffness.