Pro-Bolt Aluminum Screen Bolt Kit 4mm 9 Pk Black for Apr RSV Duc 748 749 916 999 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