Made of stainless steel and biomedical techno polymer.-The male screw is not in contact with the orthodontic acrylic resin: the function of the screw will not be influenced by the quality of the technical procedure and a non-compliant curing time.-Continuous expansion movement: the high pressure injection of the polymer allows the perfect copy of the male thread of the screw thus ensuring a steady expansion transmission without the risk of undesired turning back in the mouth.-The self-centering rectangular guides ensure a biomechanical and absolutely controlled symmetrical expansion.-The flat shape of the guides and their flexibility allow the gradual release of the expansion with a physiological orthodontic movement.