SSS produces all of its series of profiles even in stainless steel AISI 304 and 316L. The first has a chromium content equal to 18%, with a strong increase of the resistance to corrosion compared to steel commonly used in the building. However, it has a reduction in ductility and tensile strength, as well as being sensitive to sodium chloride, hydrochloric acid and sulfuric that place it at the risk of oxidation, compromising the aesthetic appearance, hygienic and functional. The AISI 316L contains instead a slightly lower amount of carbon. The nickel content and molybdenum are present to a greater extent, further increasing the resistance to corrosive agents and thereby ensuring a total defense against rust. The yield limits achieved by this material are higher (21 against ÷ 42 17 ÷ 35 Kg / mm2), with the same modulus of elasticity and tensile strength. It follows that the AISI 316L stainless steel is by far the most technically and qualitatively suitable for use in window and door from outside. This gave rise to the brand SSS PT steel, steel AISI 316L that guarantees quality, stability over time and better weldability.