The ASTM F3393-20e1 standard covers the classification and performance requirements of zinc flake coating systems. These coating systems typically contain zinc flakes, possibly with the addition of aluminium flakes, are suitable for aluminium substrates and should be free of hexavalent chromium. The standard applies to threaded fasteners with a minimum nominal diameter of 0.250 inches. It integrates the three previous ASTM standards (F1136/F1136M, F2833 and F3019/F3019M) and specifies uniform representation of imperial and metric units to ensure compliance with standard requirements.