ASTM F1137 – Coating Specification

The ASTM F1137 specification defines the critical performance and classification standards for phosphate/oil corrosion protective coatings. It is designed primarily for ferrous fasteners—such as nuts, bolts, washers, and clips—that require reliable corrosion resistance with or without a decorative finish. To implement this standard effectively, manufacturers must select from four specific grades (A, B, C, or D) based on the required supplemental coating and salt spray endurance. A key technical constraint to manage is Thread Fit; while the standard requires a minimum zinc phosphate mass of 11 g/m², the final coating thickness is strictly limited by the basic thread size to ensure proper assembly. For precision applications, threads may be produced undersize or oversize before coating to accommodate the layer, provided they maintain their specified mechanical properties.