Pro-Bolt Aluminium Screen Kit 4 Bolt Black by Pro Bolt CNC Machined from 7075T73 aluminum for a smooth finish Bolt heads are cold formed and the shanks threads are rolled Chemically brightened and color anodized to between 8 and 12 microns thick Tensile strength is 0-560Mpa; which is stronger than mild steel 60% lighter than steel and 40% lighter than Titanium